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Tow Ready Battery Isolation Solenoid

Tow Ready Battery Isolation Solenoid

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This battery isolation solenoid shuts off the 12-volt feed from your vehicle battery to 12-volt accessories on your trailer when the ignition is turned off. This lets you run the trailer's electrical components without draining your battery. 1-800-496-5010 to order Tow Ready accessories and parts part number TR118665 or order online at Free expert support on all Tow Ready products. Guaranteed Lowest Price and Fastest Shipping for Tow Ready Battery Isolation Solenoid. Accessories and Parts reviews from real customers.
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Tow Ready Accessories and Parts

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This battery isolation solenoid shuts off the 12-volt feed from your vehicle battery to 12-volt accessories on your trailer when the ignition is turned off. This lets you run the trailer's electrical components without draining your battery.


  • Hard-wired, 3-pole solenoid switches off your vehicle battery's 12-volt feed when the ignition is turned off
    • Allows you to use battery-powered electrical components on your trailer without draining your vehicle's battery
    • Grounds on your vehicle's chassis
  • Rated for 80 amps
  • 1-Year limited warranty

118665 Tow Ready Battery Isolation Solenoid

Item # TR118665

Video of Tow Ready Battery Isolation Solenoid

Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.

Video Transcript for Tow Ready Battery Boxes TR118665 Review

Today we're going to review part number TR118665. This is the Tow Ready Battery Isolation Solenoid. Now this battery isolation solenoid will shut off your 12-volt feed from your vehicles battery to your 12-volt accessories on your trailer when your ignition is turned off. This will allow you to use battery powered electrical components on your trailer without draining your vehicles battery. Now, when you do install this, the mounting bracket right here is the ground. This does need to ground to a good clean metal surface. This solenoid is rated for 80amps.

The wire we recommend when attaching wires to this is usually 10 to 12 gauge size. Now, when you do install this, basically like I mentioned, this has to be mounted into a good clean metal surface to get to ground. Right over here, this would be your voltage that would come in from your battery. Over here would be your voltage that's going out to your trailer connector. This connection right here to the ignition switch power source. That's should do it for the review on part number TR118665.

The Tow Ready Battery Isolation Solenoid. .

Customer Reviews

Tow Ready Battery Isolation Solenoid - TR118665

Average Customer Rating:  4.7 out of 5 stars   (68 Customer Reviews)

This battery isolation solenoid shuts off the 12-volt feed from your vehicle battery to 12-volt accessories on your trailer when the ignition is turned off. This lets you run the trailer's electrical components without draining your battery.


It works, guess that means I hooked it up right! Not a lot of room to work with in the 2013 Honda Odyssey but turned out good. Should have moved it a little farther forward away from the air box and drilled 2 holes but I had a space to slide the left tab in and saved a hole. Yes it is very tight and grounded good. Going on a long road trip and now we'll have piece of mind knowing we wont be stranded out in the middle of nowhere for forgetting to unhook the trailer connector.

Good looking installation. I am doing same on my 2014 Odyssey. I have not located a good place to connect my control wire to enable the relay only when ignition is on. Please suggest a location. Thanks in advance!
-- comment by: MikeE - 11/29/2014

Still working like new 1 year later. No problems at all so far.
Gerald M - 03/23/2015


Purchased this to keep my starter from potentially pulling from my trailer battery on startup. This diode (part#: RM-690) would probably have done that job just as good, if not better, but wouldn't keep the trailer plug from having live power all of the time. I did install this solenoid, though, and it's actuated by my car's 12v accessory power (on only when car is on or in accessory mode - not during ignition). Additionally, I added a rocker switch to my cars interior, right under my brake controller, so I can turn the solenoid off completely when I'm not towing. I figured this would lengthen the solenoids life, and add to my peace of mind knowing that my trailer plug doesn't have a direct line to my vehicle's battery all the time.
The solenoid itself is a little larger than I had expected, but it's been great to have so far. I'd recommend this product.

Still working well.
Dan G - 02/22/2021


This is being used as a battery isolater in a 2006 Class C RV, replacing a failed Motorcraft part. It worked after installation, we’ll see how long it lasts! Only complaint is that the terminals for the battery connections partially obstruct the mounting flange making it a little difficult to install, especially when there is not a lot of room to work.


After being energized 2 or 3 times this solenoid failed to open the circuit when denergized. After being tapped on multiple times with a screwdiver handle, it finally opened the circuit. The load was only what my Tekonsha Primus IQ brake controller with no trailer connected.
Have not checked it since the van this was installed in has been laid up for winter.

The faulty solenoid was replaced. Upon installation everything now functions properly. Customer service was most helpful and quick to solve this issue!
Tony B - 04/23/2018


Installed this on my 2013 Chev 2500HD to disconnect truck battery from slide in camper batteries when ignition is off. Chevrolet did not provide this in their stock manufacturing. Eliminates the chance of running down the truck battery when dry camping.


Kit was sufficient to completely wire my 66 F100
for Electric brakes.
I wrapped all wires under the hood with black tape and used original harness clips below the hood to cowl seal for a " factory harness" look.
Truck is almost all original and a bit rusty but it's mine..
I wired an etrailer solenoid in line to trailer power, it is energized by the ignition and I added an led toggle switch under the dash to interrupt that circuit of needed.
All the parts arrived in great condition and on time.


Good, fast, reliable service!


works like it should missing one nut had to go by one

I will have our customer service team reach out to you.
-- Etrailer Expert Jenny N - 02/20/2022


it's a simple part that just works as designed. Once installed it's good to know your trailer Isn't draining your car's battery when shut off you car and park overnight or out to dinner or lunch with the trailer cord connected. Much less likely to have any battery issues or forget to replug in the trailer and drive off and have no trailer lights working.


Replacing the battery isolator seems to have solved a number of electrical issues in my 30 year old RV. Now the engine will recharge the house battery again even though solar still does most of the work. New isolator takes a a smaller draw off the wiper circuit which also powers the cruise control. Now cruise doesn't disconnect when the wipers are turned on. Only one problem in installing. Original had slots in the mounting bracket. Replacement has holes. Both mounting screws had to be completely removed. One was quite awkward to get to. Installing could have taken 5 minutes, but because of that second screw stretched out to maybe 20 minutes.


Works well. I wish it was a bit smaller but it is high amperage.


Used this isolate trailer battery from car battery. This is third one I've installed and it works great. Learned something this time to clean up the wiring install. Window washer wire was right next to battery where this was installed so used that wire to hot it up when ignition is on.


the battery isolater solenoid works perfect when wired correctly when protecting my truck battery from my trailer winch battery when the winch is in use I highly recommend this product.


My camper stopped charging the coach battery. Tested an found the isolator wasn't
passing power thru. Searched online and this was the least expensive (by far in some the cases). Quick shipping, easy install and charging again. I am a happy camper!

One year later - working beautifully !
Timothy - 09/04/2019


Does exactly what I needed; prevents the trailer from discharging the tow vehicle battery when ignition is turned off.


Used to isolate my wench, from the truck battery, when in use. Then I can connect back to charge both batteries while driving and wench is idol. delivery was fast through USPS.


It's a relay/solenoid!

Works great
so far. We got this to wire our small teardrop for underway charging. I found an ignition-switched voltage source in the engine bay, and now I don't have to think about whether or not I've unplugged the trailer.

Would use again.


Working well.


only complaint is that no instructions came with this part.

The product description overview video linked above will actually run you through how to wire the solenoid. The terminal on either side is used for the incoming and outgoing power it doesnt matter which terminal is used for which and the center terminal is used to an ignition switched circuit. The radio circuit is frequently used, because it powers down when the ignition is off.
-- Etrailer Expert Mike L - 11/21/2018


My truck came with only a four pin trailer connector. I installed a seven pin connector received from etrailer and realized I needed to prevent battery drainage on my truck caused by the trailer battery charging when the truck engine wasn't running. The battery isolation solenoid provided a perfect solution. Great product at reasonable price.
As usual etrailer exceeded my expectations with next day delivery.


The product was exactly what I wanted for the amount I was told it should cost. I wish there would have been instructions there just to make double sure I know what I'm doing but it's easy to find it online.

Ive been remiss at installing it. I think I know what to do now but Im still somewhat unsure. Again, the directions would have been easier to do if there were a bit more there.
Kelly H - 01/04/2018


Works great in the circuit I installed in my truck to charge my trailer battery while driving. Etrailer is my go to for my rv needs. Great prices and fast shipping are the norm.


Would love to see a wiring diagram or instructions/video for install on etrailer. Otherwise good part.


Had to change my order after submitted on the web and that was done quickly with help from a great customer service rep. Received the order quickly and all parts were as expected. Love the online video provided by etrailer in helping to chose the right product and installing it, it is hard to improve on perfect.


NO INSTALLATION INSTRUCTIONS included as promised!!!
I was told when I ordered that printed wiring diagram would be included in package. No instructions were included with the product or on package. Had to call CS and go online to find them. Not too tough but needed clarification on which post was power in and which is power out. Just frustrating being told one thing at time of order and not receiving as promised.
Product works as intended.

Show More Reviews

See what our Experts say about this Tow Ready Accessories and Parts

  • Where Does Battery Isolation Solenoid Install and Can Vehicle Alternator Overcharge RV Batteries
    The battery isolation solenoid, # TR118665, is usually installed in the engine compartment. There are several possible ignition sources you could use. The radio is a popular choice. What you could do is use a fuse tap for the radio fuse and run the wire to the 12 volt input on the solenoid. Any 12 volt source that only has power with the key on will work. The vehicle alternator would have to be very, very strong and the wire gauge used very large for the alternator to be able to push back...
    view full answer...
  • Voltage Drop Across Tow Ready Battery Isolation Solenoid
    I spoke with my contact at Tow Ready and he said the Tow Ready Battery Isolation Solenoid, part # TR118665, is a simple on/off switch so you can expect to see no appreciable voltage drop. If you have 12 volts going in you will have 12 volts going out.
    view full answer...
  • Tapping into a 12 Volt Source on a 2001 Chevy Silverado
    What you may need to do is splice into one of the wires going into the radio that is only hot when the car is on rather than use a fuse tap. Or any accessory that only receives power when the ignition is on such as a radio, antenna, windshield wipers to name a few. If you are looking at the 12v sticker on the solenoid # TR118665, right above it will be the auxiliary center post which is usually attached to an ignition switch wire.
    view full answer...
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  • Can Trailer Battery Be Overcharged when Charged from 12 volt Accessory 7-Way Circuit
    When using a 12 volt trailer accessory wire to charge a trailer battery it would be nearly impossible to overcharge it. The max voltage the battery would ever potentially be would be the same voltage of the 12 volt accessory circuit. Also, these circuits generally don't have much amperage because of the smaller gauge wire used from the vehicle battery back to the trailer battery. Long story short, you wouldn't have to worry about overcharging the camper battery. If anything you would be...
    view full answer...
  • Can Running Light Circuit be Used with Battery Isolation Solenoid # TR118665
    If you are looking to use the Tow Ready Battery Isolation Solenoid, # TR118665, on the running light circuit to possibly provide a maintenance charge to a battery on a trailer then yes, this can be done. Please keep in mind that the battery isolation solenoid will only be active when the running lights are on. If you are looking for a different set-up, please send me an email with additional details and I will be happy to help.
    view full answer...
  • Solenoid Recommendation for Activating 12 Volt Circuit for Powering Inverter on Trailer
    For an isolation solenoid you would want the part # TR118665. Basically you would run a keyed power source wire to the center post to activate the other two posts of the solenoid only when the truck is running or key is on. The outside posts would run from the battery to a wire to use for powering the lights/inverter.
    view full answer...
  • Does Center Pin of Tow Ready Isolation Solenoid TR118665 Need a Fuse Protection
    You would not need to fuse the circuit that powers the center pin of the part # TR118665. This only draws 1/2 an amp and does not power anything so circuit protection would not be needed. It's only function is to close the circuit to let the voltage pass through the other two pins.
    view full answer...
  • Typically Where to Find Keyed Power Source for Installing Isolation Solenoid
    You will have to find a circuit that only sees power when the key is on. Typically the ignition circuit at the fuse box will work well for this. You can use a fuse tap to tap into that circuit. Or if you want to find a circuit within your vehicle typically the radio circuit or cruise control circuit can be used for this.
    view full answer...
  • Solenoid Recommendation To Prevent Trailer 12 Volt Acc Circuit From Being Active When Key is Off
    We have just what you need. To prevent the vehicle battery from being inadvertently discharged, you can make sure the trailer is unplugged when the vehicle is turned off or you can install a battery isolating solenoid like part # TR118665. The solenoid would be wired according to the photo I edited for you. When the center pin of the isolator is wired to an ignition powered power source (a circuit that only has power when the ignition switch is turned on), the power feed will only be active...
    view full answer...
    Image 1 for
  • Installing Battery Isolation Solenoid For Trailer Battery In 2001 Dodge RAM 2500
    The Tow Ready Battery Isolation Solenoid # TR118665 can be used to protect your vehicle battery. The battery gets connected to one side, the accessory/ignition gets connected to the middle and the other side gets connected to your trailer battery. You can connect this solenoid anywhere you want in that system. The mount is the ground, so you want a clean connection to metal there, but you can use whatever wire you want to connect to your accessory/ignition to ensure that your vehicle...
    view full answer...
    Image 1 for
  • Operating Temperature & Power Draw of Tow Ready Battery Isolation Solenoid TR118665
    The Tow Ready Battery Isolation Solenoid # TR118665 will get warm to the touch when it has been passing current continuously. The center terminal which takes in the trigger signal to close the solenoid and complete the circuit will draw 12V at a fraction of an amp. My contact at Tow Ready did not have an actual current spec but he noted the power draw is minimal.
    view full answer...
  • How to Allow 12 Volt Accessory Circuit of 7-Way to Only Come On When Key is On
    Sounds like you are talking about the 12 volt accessory circuit of a 7-way trailer connector. For some vehicles with factory 7-ways the circuit is only active when the key is on. Most however are on all the time. If the 7-way was hardwired to the vehicle then it will be on all the time unless an isolation solenoid was installed like part # TR118665. Basically this gets wired inline with the circuit and the center pin, when wired to a power source that is only active when the key is on,...
    view full answer...
    Image 1 for
  • Trailer Brakes Lock Up When Connected to Truck Draining Truck's Battery
    Leaving your trailer connected to your truck overnight will definitely drain the truck's battery. The way to prevent this is to install a battery isolation solenoid # TR118665 on the truck. The volt circuit on your trailer is a constant circuit so it will always provide power through the 7-way. What do you mean you unhooked the trailer breakaway battery? Did you pull the pin? If you pulled the pin and provide power to the trailer the brakes will lock up. Normally it would charge the...
    view full answer...
  • Can Either Pole of the Tow Ready Battery Isolation Solenoid be Used as Input/Output
    Either side of the Tow Ready Battery Isolation Solenoid part # TR118665 can be used as the input or the output. I confirmed this with my contact at Tow Ready.
    view full answer...
  • Can a Horse Trailer Wired for 110AC Power Also be Wired to Run Off of 12 Volt DC Power
    Since you want the powered accessories on the trailer to run off of both 110 AC power and 12 volt DC power you will need what is called a transfer switch and probably some additional wiring including the batteries. A transfer switch will automatically switch to running off AC power when the trailer is plugged in and then revert back to DC power. The trouble is that the accessories using the power have to be rated for AC and DC power. This is actually a fairly major operation. We do...
    view full answer...
  • Can Lights, Jack, and Winch be Powered by 12V Circuit Coming From Tow Vehicle
    The function of the Tow Ready Battery Isolation Solenoid, # TR118665, is to shut off the 12-volt feed from your vehicle battery to 12-volt accessories on your trailer when the ignition is turned off. This lets you run the trailer's electrical components without draining your vehicle's battery, assuming that you have a trailer mounted battery. The isolation solenoid is designed to be mounted on the tow vehicle because it requires an ignition switched power source in order to function. By...
    view full answer...
  • Amps Required to Close Circuit on Tow Ready Battery Isolation Solenoid # TR118665
    I spoke with my contact at Tow Ready and it requires 1/2 of an amp in order to close the circuit and keep it closed.
    view full answer...
  • Installation Instructions for the Tow Ready Isolation Solenoid part # TR118665
    I do not have specific installation instructions for the Tow Ready Isolation Solenoid part # TR118665 on your 2004 Ford Explorer, but I can describe how it would install on your vehicle. Using the picture I attached as a guide you run a wire from the positive terminal of your vehicle battery to the post on the left, and then on the right side of the solenoid you will run wire to whatever accessory you are looking to power. The middle terminal will need signal from a power source that only...
    view full answer...
    Image 1 for
  • Ways to Wire Multiple 12V Batteries
    Multiple batteries can be wired either in parallel or series configurations to deliver either increased amp-hours or increased voltage. Eight 12V batteries wired in parallel will deliver the same 12V output but with a longer amp-hour capacity. Eight 12V batteries wired in series will deliver more voltage (8 x 12 = 96 volts) with about the same amp-hour capacity. If your solenoids are burning out in your application you will want to use a higher-rated unit.
    view full answer...
  • How to Get a Higher Rated Reverse Light Circuit on a Vehicle with LED Reverse Light
    I have a solution for you, but a reverse light circuit setup for an LED would most likely be too low rated amperage wise for what you are trying to do so that is why you are experiencing the problem you have. You are going to need to get an isolation solenoid like part # TR118665. You would need to run the reverse light circuit of your vehicle to the center post of this and then run a wire from the vehicle battery to one side of the outside pins and then the other side will be a reverse...
    view full answer...
  • Could the Tow Ready Isolation Circuit TR118665 Activate with Trailer Running Lights
    The center pin of the Tow Ready Battery Isolation Solenoid # TR118665 can have basically any power source run to it for allowing the circuit to complete. If you wanted to wire this up so that the power output of this solenoid is active when the running lights are on then this would work well for that. If you are looking for a keyed power source that is on all the time when the vehicle is on then the running light circuit would not be the correct circuit to use. You would need to use something...
    view full answer...
    Image 1 for
  • Tail Light Pin Of Trailer Wiring Harness On 2011 Volvo C70 Shows Voltage All The Time
    Showing voltage at a pin on a connector like the Curt T-Connector Vehicle Wiring Harness, part # C56119 that is designed to fit your 2011 C70 is common. This just means there is voltage available and since nothing is connected to the harness, there is no amperage draw. This will not drain your C70 battery. If you want to cut off all power to the harness you can install a battery isolator like part # TR118665 inline to the wire connected to your positive battery post. This gives you the...
    view full answer...
    Image 1 for
  • Durability of Tow Ready Battery Isolation Solenoid 118665
    Since the terminals are exposed on the solenoid, this is an item you wouldn't want to get too wet, and is not weatherproof. For your convenience I've linked a video of the Solenoid installed on a vehicle under the hood.
    view full answer...
  • Will Truck Bed Camper Battery Charge From Vehicles Battery via 7-way Connector
    The vehicle battery will only provide a maintenance charge to the camper battery. It will not increase the camper battery charge level. When the camper connector is plugged into the vehicle, the vehicle's battery is supplying power to the camper, but it is not charging the camper's battery. The indicator light is likely coming on because of the power supply, not because of a charge. If you want to keep the camper plugged into the vehicle while the truck is off, I do recommend installing...
    view full answer...

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