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Author Topic:   Trailer Brake, Turn Signal Lamp Wiring
jeremiahups posted 03-31-2009 08:31 AM ET (US)   Profile for jeremiahups   Send Email to jeremiahups  
I just got my first boat, which means I had to add a trailer hitch to my wife's SUV. The wire harness for my wife's Pacifica SUV connected very easily behind the tail lights. The SUV light work fine; both brakes and signal work as normal. However, the trailer lights do not. The brake lights work when pressed but the turn signals are not working at all. I checked all connections and nothing seems to be wrong. The brake and turn signal lights are one in the same as this is a small trailer. Could I have a problem with the wiring harness, could it be bad and I need a new one, although this one is brand new.
Buckda posted 03-31-2009 09:31 AM ET (US)     Profile for Buckda  Send Email to Buckda     
Well, there are a couple of possibilities.

For the record, I'm fighting this very problem on my rig since late last summer.

The symptoms of the problem are the lights not working properly.

The source of that problem is likely that you have blown a fuse. Many vehicles with factory tow packages have extra circuits that protect the rest of the vehicle lighting if there is a short at the trailer.

...the short on the trailer is likely the problem.

Here is something that is worth the price (3.99): http:/ / www. basspro. com/ webapp/ wcs/ stores/ servlet/ Product_10151_ -1_10001_58362?cm_mmc=froogle-_-225-10-6-_--1-_-38-525-006-00& hvarAID=f roogle& mr:trackingCode=AA29018C-6519-DE11-B0EA-001422107090& mr:referra lID=NA

Here's how you work it - plug in the tester and check the LED's to make sure all circuits are 'go' from the vehicle.

THEN, plug in the trailer to the tester. If the trailer lights still don't work, but the tester lights are on, then you have a trailer wiring or lamp problem and not necessarily a short. If you blow the circuit on the vehicle, you have a short somewhere.

The problem can be from blown lamps in the lights, or it can be a frayed or pinched wire that is shorting out to the trailer frame....or it could be a bad ground.

Hope that helps narrow it down for you.


Buckda posted 03-31-2009 09:34 AM ET (US)     Profile for Buckda  Send Email to Buckda     
Oh - and my solution on my trailer is that I plan to re-wire it over the weekend if the weather holds out. I'm going to run the wiring through pvc piping zip-tied to the inside channel on my galvanized "C" beam trailer frame to protect it from chafing, pinching and shorting.

If you have a steel trailer with the wiring running inside the frame, check to make sure that all the rubber grommets are still there to protect the wires when they come out or go into the frame - this is a common chafe/fail/ground/short point for the circuit.

Buckda posted 03-31-2009 09:37 AM ET (US)     Profile for Buckda  Send Email to Buckda     
Oh geez, I just re-read your question. You added this circuit? I'm trying to remember if the pacifica has seperate orange turn signal lamps in the back? If so, I believe you will need an adapter to make this work, as the brake/turn signals are on separate circuits. Check your owner's manual or consult with the dealership on how your vehicle's wiring is set up.

Buckda posted 03-31-2009 01:48 PM ET (US)     Profile for Buckda  Send Email to Buckda     
Here you go: Mopar-OEM-Chrysler-Pacifica-Trailer-Tow-Wiring-Harness-Kit-P20192C5756. aspx
jimh posted 03-31-2009 06:54 PM ET (US)     Profile for jimh  Send Email to jimh     
On many modern vehicles there are separate circuits for illuminating the turn signals with isolation from brake signals. To adapt a vehicle with separate brake and turn signals to a trailer that uses common brake and turn signals, you need to wire a convertor into the circuit. The converter really consists of nothing more than a four ($0.25) diodes used to steer the lamp current.

On some modern vehicles the circuitry providing the 12-volt current for the tail lamps, brake lamps, and turn signals has very limited current capacity. To operate trailer lamps a special adapter may be required. The adapter uses an auxiliary 12-volt feed as the source of current for the trailer, and it uses the vehicle lamp signals as driver signals. This minimizes the added current load on the vehicle lamp circuits

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