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sprinkles08
sprinkles08, Chrysler/Dodge/Jeep master tech
Category: Dodge
Satisfied Customers: 22985
Experience:  ASE Master and Advanced Certified, Chrysler/Dodge/Jeep Master Certified, Trans and Hybrid Specialist
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99 dodge ram 2500 4x4 diesel. brake lights stay on

Customer Question

99 dodge ram 2500 4x4 diesel. brake lights stay on constantly no matter what. even with key off, brake light switch unplugged, relay unplugged, trailer harness unhooked. only way to get them to turn off is to unplug main fuse or turn signal switch. there is no trailer brake controller.
Submitted: 1 year ago.
Category: Dodge
Expert:  Dan replied 1 year ago.

Let me know how the different turn signal switch goes. Sounds like you are on the right track.

Customer: replied 1 year ago.
I tried another turn signal switch and they stay on still.
Expert:  Dan replied 1 year ago.

Sounds like you have a short feeding the brake lights, Closely look at the trailer hitch wiring especially if it is aftermarket.

Customer: replied 1 year ago.
ok will check it out. get back in a few.
Expert:  Dan replied 1 year ago.

Ok sounds good.

Customer: replied 1 year ago.
is there any way you could help me find a wiring diagram for the harness that runs down the drivers side frame to the tail lights? found a massive rats nest of corroded twisted togethered wires. its bad.
Expert:  Dan replied 1 year ago.

I dont have access until monday. I will opt out and another expert will be able to help.

Customer: replied 1 year ago.
ok thank you!
Customer: replied 1 year ago.
I fixed the mess in the rear of the truck and ruled out any shorts from the rear of the truck up to the front of the cab at the main plugs where it runs up to the the top. going to keep searching.
Expert:  sprinkles08 replied 1 year ago.

Hello and welcome to JustAnswer!

If the lights stay on with the brake switch unplugged then you definitely have voltage bleeding in from somewhere. It may be a short in the harness somewhere or it could be a poor ground causing current to flow from another component through the brake lamp circuit.

Do you have a remote start?

Customer: replied 1 year ago.
No remote start. I fixed a bunch of wiring in the back where i thought it would be. Looked at every bit of wiring from front to back. Pulled part of the dash a part to look. And. Nothing. I unplugged the plug that connects harness behind drivers side front wheel amd they go out. Also i unplugged main plug under dash where the switch is tied into. And they go out and there is no power on the white with brown tracer output wire anymore. So it is between that and the pdc but just cant seem to find it.
Expert:  sprinkles08 replied 1 year ago.

The brake lights now do go off when you unplug the brake switch?

Customer: replied 1 year ago.
No. Just when i unplug the main plug under the dash. Not the actual switch. They stay on when i unplug brake switch no matter what. Theres a large connection point left of the brake pedal.
Expert:  sprinkles08 replied 1 year ago.

I think you're referring to the bulkhead connector then.

Can you plug it back in, unplug the ABS module and see if anything changes?

Expert:  sprinkles08 replied 1 year ago.

If you need any more help let me know.

Customer: replied 1 year ago.
I do. Sorry for the delay its been one of those weeks. Im going to mess with it first thing in the morning and well get back with you
Expert:  sprinkles08 replied 1 year ago.

Sounds great!

Customer: replied 1 year ago.
Okay. Finally got to messing with it again. Got ahold of a scan tool and codes 65 internal master relay open and 36 no signal rear speed sensor. Could that be a reason the lights on the truck stay on. Along with the dash lights?
Expert:  sprinkles08 replied 1 year ago.

Neither of these codes would be related to lights staying on.

Is the instrument cluster illumination staying on without the park lamps being turned on?

Customer: replied 1 year ago.
I forgot i had the brake light fuse in pdc unplugged while it sat and that was the open code for abs and brake. Sorry. But i am desperately trying to find a wiring diagram to see which wire is constant and output for sure just to make sure. And also when hooked to a scanner yesterday i could not communicate with the bcm. But i could with everything else if that helps any.
Expert:  sprinkles08 replied 1 year ago.

It doesn't have a BCM so nothing to worry about there.

What lights are coming on inside when not intended?

Customer: replied 1 year ago.
There are no dash lights now. Abs was intermittent for speed sensor on diff. But not on now. Ive tried to run a seperate wire from my output wire on brake switch to output wire back by brake lights. Wire works now with brake switch but lights stay on still. Then if there is no bcm. What is module on firewall passenger side behind air box?
Expert:  sprinkles08 replied 1 year ago.

The powertrain control module is on the firewall behind the airbox.

Did you unplug the ABS module to see if the brake lights went out?

Customer: replied 1 year ago.
unplugged abs module and lights stay on.
Expert:  sprinkles08 replied 1 year ago.

I'm a full time tech and at work this afternoon, I'll get back to you as quickly as I can!

Expert:  sprinkles08 replied 1 year ago.

Do you have an aftermarket remote start, alarm?
Do you have trailer wiring?

Customer: replied 1 year ago.
No remote start or alarm. But do have trailer wiring. It is all new and i can isolate it completely and they stay on.
Expert:  sprinkles08 replied 1 year ago.

If you unplug the multifunction switch do the lights go off?

Customer: replied 1 year ago.
they do. Bought a new one to try and they came back on. There is a chance i got a bad one but i think it is unlikley.
Expert:  sprinkles08 replied 1 year ago.
Do you have a trailer brake controller?
Customer: replied 1 year ago.
No just the factory plug underdash for one.
Expert:  sprinkles08 replied 1 year ago.

The third brake light is on it's own circuit. Is it staying off?

Customer: replied 1 year ago.
it stays on as well.
Expert:  sprinkles08 replied 1 year ago.

With the brake switch unplugged also?
Have you always owned the truck?

Customer: replied 1 year ago.
with it unplugged as well. No i bought it about 2 years ago. I replaced the trailer plug and harness with a kit from e trailer.com but that was a year before this started happening amd i can take it out of the circuit anyway. But other than that the truck is pretty much unmolested.
Expert:  sprinkles08 replied 1 year ago.

If you haven't disconnected the trailer wiring we need to do so before proceeding.

Customer: replied 1 year ago.
I already have. One of the first things i did.
Expert:  sprinkles08 replied 1 year ago.

I'm a full time tech and at work this afternoon, I'll get back to you as quickly as I can.

Expert:  sprinkles08 replied 1 year ago.

Can you remove fuses one at a time to see when/if the lights go out and let me know which fuse turns them off?

Customer: replied 1 year ago.
The only one that turns them off is the 20 amp maxi fuse in the pdc for brake lamps
Expert:  sprinkles08 replied 1 year ago.

Are you able to see any wiring modification that has been done at any point? The brake switch power supply is somehow shorted to the output circuit.

Customer: replied 1 year ago.
None besides the aftermarket trailer plug harness. Which is a direct fit for the truck. And the radio wiring is after market.
Expert:  sprinkles08 replied 1 year ago.

You're probably going to have to hard wire the switch output circuit and cut the old wire if you're unable to visually see any issues.

Under the large bulkhead connector under the left side of the dash there is a smaller connector (C203). Can you unplug it and see what effect that has?