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Tow Ready Battery Isolation Solenoid

Tow Ready Battery Isolation Solenoid

Item # TR118665
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Tow Ready Battery Boxes - TR118665
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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. Great prices 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 - TR118665

  • Battery Boxes
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  • Tow Ready

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

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 Satisfaction Score:

Customer Reviews

Tow Ready Battery Isolation Solenoid - TR118665

Average Customer Rating:  4.7 out of 5 stars   (69 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


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.


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


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.


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


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


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.


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


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.


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.


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.


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.


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.


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.


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


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.


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.


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


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


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.


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


Good quality, continuous duty, perfect fit. Using as battery switch between start and house batteries on my boat. Flip a switch and go, no longer have to get up and go to the stern and crank a manual switch on a bouncing boat in rough water.


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.


Big, strong and versitle. Battery will power Brakes, power lift , winch and breakaway.

Show More Reviews

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

  • 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...
  • Does Center Pin of the Tow Ready Isolation Solenoid TR118665 Need a Fuse
    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...
  • Does the Battery Isolation Solenoid Ground to a Metal Surface Through the Mounting Hardware
    You will need to mount the isolation solenoid # TR118665 to a metal surface. This unit does ground through the mounting location. It will not function if it is attached to plastic so you will need to locate sufficient metal space so it will function correctly.
    view full answer...
  • Using TowReady Battery Isolation Solenoid, Part # TR118665, When Operating Trailer Winch
    The Tow Ready Battery Isolation Solenoid, part # TR118665, protects your tow vehicle battery from excessive drain when using 12V trailer accessories by isolating the vehicle battery. It is operated by the vehicle ignition switch, so in order to isolate the tow vehicle battery from current draw from the trailer winch, the tow vehicle ignition key does have to be in the off position. This will let the winch pull power from the trailer battery rather than the vehicle battery. Please refer...
    view full answer...
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  • Where to Get 12 Volt Ignition Source Power for a battery Isolator on a 2003 Toyota Tacoma
    There are various circuits that are only hot when the vehicle is turned on. The radio is one. You could find the fuse that powers the radio and then use a fuse tap to tape into it and wire it to the center post on the isolation solenoid # TR118665. Use the vehicle owners manual and/or legend on the power distribution box lid to locate a relevant fuse. Fuse taps are available at auto parts stores.
    view full answer...
  • 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...
  • 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...
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  • How to Wire the Tow Ready Battery Isolation Solenoid, # TR118665
    I spoke with my contact at Tow Ready regarding how to wire the Tow Ready Battery Isolation Solenoid, # TR118665. He stated that, if you are looking at the unit with the dome facing up and the 12v sticker right side up (like we have it shown in the picture on the product page), the left terminal is input, the right terminal is output, and the middle is auxiliary which will be connected to a source that will act as a switch to engage/disengage the solenoid. He stated that normally, the middle...
    view full answer...
  • What is the Amp Rating of the Tow Ready Battery Isolation Solenoid, part # TR118665
    I spoke with my contact at Tow Ready and he informed me that this Tow Ready Battery Isolation Solenoid, part # TR118665, is rated for 80 amps continually and can handle spikes up to 100 amps. He also said that a 160 amp spike will permanently damage the unit.
    view full answer...
  • Is Battery Isolator Needed On 2008 Ford F250 With Trailer Tow Pkg
    Since your 7-way connector is only hot when the key is turned on, a battery isolator solenoid would not be necessary. Since this is not the case with all vehicles, it may be good practice to unplug the trailer from the vehicle when not being used.
    view full answer...
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  • Will a 130 Amp Alternator Cause Problems with 80 Amp Rating of Tow Ready Battery Isolation Solenoid
    As long as you install the Battery Isolation Solenoid, # TR118665, correctly (see photo) and the items you are powering on the battery isolator output circuit does not draw more than 80 amps you will not have any problems. In most cases the battery isolator is installed on the charge line going to a trailer connector at the back of a vehicle and this circuit is used to maintain the trailer batteries charge and/or power utility lights in or on the trailer. In this situation your alternators...
    view full answer...
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  • Can 8 Gauge Wire Be Used in OEM Trailer Connector on a 1998 Dodge Ram 2500
    On plugs like the one in your picture there is normally a locking device that holds the wires in place. Pulling them out without first removing the locking device could result in damage to the connector. You will need to look for anything that looks like it might be a retaining device. You will most likely need to use a very small screwdriver to depress a tab or push in something to release the wires. The other way to do this is to bypass that connector all together and run the wire from...
    view full answer...
  • Battery Isolation Solenoid Not Working Properly on 2001 Chevrolet Silverado
    First I would look at what you have mounted the isolation solenoid # TR118665 to. You will need to mount the isolation solenoid to a metal surface. The unit grounds through the mounting location. It will not function if it is attached to plastic so you will need to locate sufficient metal space so it will function correctly. I can't tell from your photos if you are mounting the isolation solenoid to a plastic or metal surface. The ground you have made to one of the screws holding the unit...
    view full answer...
    Image 1 for
  • Recommended Mounting Location for Tow Ready Battery Isolator # TR11855
    I spoke with my contact at Tow Ready regarding your question. I would refer to the battery isolator as being weather resistant, but NOT weatherproof. I would recommend installing the isolator in a more protected spot than under the truck bed. Installing the isolator in the engine compartment, where it would be a bit more protected would be the best bet.
    view full answer...
  • 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...
    Image 1 for
  • 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...

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