Synergy

2005 - 2500 Dodge RAM
My taillights have me stumped. The brake lights stay on all the time, the back-up lights don't work and now my trailer brake locked up when I backed up while hauling a horse over the weekend (it was raining at the time).
I have been checking over the wiring and the only thing I have found is some corrosion on the connectors that connect the wiring to the tail light, could this be behind the problem? I have been told no by the trailer repair guy, but he also told me that it was the brake light switch (which I replaced, but it didn't help). The brake light on the instrument panel stays on, only brake not ABS.
I keep thinking ground fault? Just not sure where.

pind

Tail light bulb filament broken and touching the other filament. Start there

gcssr

The trailer brake locking up when u back up is probably in need of adjustment,adjust brake until wheel locks up, then back off 6 to 8 clicks it will free wheel. The dash brake light could be the emergency brake petal is not fully released, set brake and release see if light still on, do u use this trailer all the time sounds like u have wiring problems

Synergy

The brake light controller is disconnected and it only did it when it was raining really hard. I did figure out that the truck was likely used to take boats in and out of the water as I bought it from a marine supply shop. I will likely have to replace a lot of wiring 😣

Green_Machine

1) Download manual here:

2003 Dodge Ram Manual- Online PDF - DODGE RAM FORUM - Dodge Truck Forums

It's for a 2003, but is likely 99% the same.

2) Look at page 8W-33-6. See how the one contact on the brake switch (Terminals 1/2) illuminates the cargo brake light, and also keys the trailer brake and the instrument cluster?

This would be where I would troubleshoot, the L50/18/WT/TN wire...looks like it must be going positive somehow.

Understand that the wire to the instrument cluster raises a digital point in the PCI bus system (Digital communication system) which connects the instrument cluster to the integrated power module (IE: Computer controlled fancy fusebox). The IPM reads the PCI bus, sees the point on and causes a relay to close in the IPM which sends power to the rear brake lights. They call this a 'light driver'.

You can see the IPM output on page 8w-51-5, and 6. Also there are the backup light circuits.

Anyway, if you are getting all the brake lights and the brake controller operating, it must be in common to all these things, and the switch/ wire is the only thing I can find which meets the symptoms.


The backup light may very well be a seperate issue as well, either bulbs or PDC or even trans switch.


Chay

Synergy

Awesome thanks Chay!!! I am at my wits end as I have still not found the fault and now my trailer brakes kick in when I back-up with trailer attached.

Green_Machine

Sounds like perhaps the trailer brake wire and the reverse light wire are tied together somehow.

Not sure how that could happen.

I would identify and put a voltmeter on the brake wire, then block the vehicle and move into reverse and see if it lights up, then go from there.

Good hunting.

Chay

realfast

I have been having the same issues! They would work correctly then the would not. blinkers would work correctly as long as engine was operating above 1000 rpm! Talk about making me scratch my head. Then this morning i started cutting and soldering taillight connections(flatbed) still working off and on. DANG!!! Then i noticed a low glow on back up lamps i talking less than a birthday candle come to think of it about as bright as flash lite when I got it back from my wife! LOL Then i found it A BAD GROUND should have started there but i aint a electrician. Maybe you are having the same issues. Check you grounds.

jumper

Since your brake lights are on all the time and the back of the truck had been dunked a lot, perhaps even in saltwater (?), I'd focus first on the seven- and four-pin trailer connectors at the rear bumper that bring all things brake, power, ground, reverse, and turn together in one spot. Start disconnecting the harness there, looking at grounds, and working your way forward. You'll find it.

torquefan

Yep, for stuff like that I'd definitely go right to the 7 pin trailer connector and look inside the back of it. They like to scoop up gunk and moisture that will partially short between any of the pins.

Mexstan

Some time ago I had similar weird problems. It started with the tail lights and trailer brake lights staying on all the time, even with the plug at the brake switch disconnected. Checked all the wiring on the plugs at the back of the truck, but everything was clean with no corrosion. Finally disconnected the trailer brake controller completely and the lights worked fine except that there was a 2 - 3 second delay for when the brake lights came on after depressing the brake pedal. There was another 2-3 second delay for them to go off after taking my foot off the brake pedal. After much head scratching and looking at the electrical schematics decided to start from the battery and work backwards checking everything. When I got to the brake light fuse I pulled it just to see what the connections looked like. Much to my surprise it was burned. What???? So how could the brake lights come on with a burned fuse???? Replaced the fuse and everything has worked fine ever since then.

Still not sure what caused this, but presume that there is some sort of feedback from the brake controller or something else in the circuit that I cannot see in the schematics.

When I was having all these problems I took my truck to a five star Dodge dealer in Texas to have the airbag recall stuff taken care of. While it was there I asked them to take a look at the delay in the trailer brake lights. Their electrician spent the entire day troubleshooting and even spoke to Star, but could not find the cause and admitted defeat to me. They did not charge me for this work.

47Dodge

As a few others have stated I would check the 7 pin trailer plug at the back on your receiver hitch. It sounds like something is loose and causing you to back feed into the other light circuits. The 2nd gen trucks were famous for one wire coming loose and blowing the fuse causing you to lose all your rear lights. On my 2nd gen the 7 wire harness had just enough length to go into the plug on the rear and when it came loose there was enough tension on the harness it plugged back contacting the frame and popped the fuse.


I bet going into reverse the circuit for reverse lights is energizing the trailer brake circuit somehow causing your brakes to come on. And when not its back feeding causing your other lights to wig out.




47