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Trailer Wiring Harness with Circuit Protection Recommendation for a 2001 Dodge Dakota

Question:

My 2001 Dodge Dakota owners manual says, Towing a trailer equipped with more than the standard lighting turn, tail, stop and backup lights may cause an abnormally high electrical current draw through the headlight switch, causing the switch to fail. To prevent a recurring switch failure install a trailer tow wiring harness overlay kit with relay to bypass headlight switch. Does anyone make such an after-market overlay kit? If not, or if too expensive, what parts would be needed to make one? How would it be wired? Am I being overly concerned? Are many travel trailers equipped with more than the standard lighting? My owners manual also says, Connect trailer lighting and brakes using factory harnesses only. Do not cut or splice any wiring to the brake circuits. I just purchased the truck. Good price, low miles. It has an after market hitch with a flat-four connector tied into the vehicles tail lights. I want to pull a travel trailer with a dry weight of less than 4,000 lbs. Vehicle tow limit is 5150. 2001 Dodge Dakota Club Cab SLT - 2wd - 4.7L V-8 - 136 amp alternator - 4 sp automatic w. OD - 3.55:1 rear axle ratio

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Expert Reply:

Splicing in a trailer wiring harness is a pretty common practice even though almost all vehicle manufacturers do not recommend doing so. This is because trailer lights will put an additional load on the tail light circuits that vehicle manufacturers usually do not account for. The more lights a trailer has, the larger the load on the tail light circuits.

Standard lighting on a trailer usually consists of two tail lights, two brake lights, two turn signals and two side marker lights. Many trailers do not have backup lights, but a standard number of backup lights would be 2. If your trailer has more lights than the standard lighting, you could change the lights to LED lights which draw a fraction of the power that standard incandescent bulbs draw. This would put a significantly smaller load on the tail light circuits.

Another option that you have is to install a trailer wiring harness with a powered converter like the Tow Ready Heavy Duty Modulite Wiring Harness, # 119190KIT. Since you already have a 4-way wiring harness on your truck, you can cut the 4-pin connector off and splice those 4 wires to the blunt cut wires coming out of this converter box. You will just splice them color for color and ground the red wire with the white ground wires (see photo).

The last wire you will see on this harness is a thicker gauge black wire. This wire will run to the positive post of your truck battery via the included fuse holder. This Modulite will actually draw its power from the vehicle battery to power the trailer lights so there is no additional load on your tail light circuits. The converter box uses the signals from the tail light circuits to know when to send power to the trailer lights, but the power does not actually come from the tail light wires. I have attached a help article with tips on routing the power wire for the harness for you to check out.

This harness would act in the same way as the overlay kit and relay that you mentioned. You are not being overly concerned, I would recommend installing the Modulite harness. It is always best to pull power from your battery rather than your vehicles tail lights for trailer lights on any vehicle. This harness also acts as a circuit protector for your truck. If it detects a short circuit or overload on your trailer the converter box will stop working preventing the issue from back-feeding onto your vehicles tail light circuits.

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John H

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