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Brake lights not working

875 views 7 replies 4 participants last post by  bigfish95971  
#1 ·
I have a 2001 dodge 2500 that I was towing a trailer with, something shorted and took out tail lights and brake lights blinkers still work. I fixed the tail lights it was just a fuse but the brake lights fuse was not blown. I read 12.9 volts across my battery 9.49 across the pins for the fuse and I get 4.1 volts at the lights (leds slightly light but not very bright) I have changed the brake switch at the peddle and I know it is good works fine in another truck. If I disconnect the lights at the rear the volts on the wires jump up to the 12 volts they should be at. No burnt connections.
 
#2 ·
Sounds like your describing voltage drop. V=I/R. When checking with your dvom, needs very little power to make voltage signal. So reads 12. As soon as you put a load on the system, voltage drops heavily from resistance. When voltage drops amps increase and can blow fuses.

I would check and clean grounds and all connections and see if that improves. I suspect @bigfish95971 will be by soon to show some pics of his grounds. Also Ill recommend W-T ground mod while here.
 
#4 ·
W-T is a username who came up with the mod. You can search for other articles he’s written on mopar1973mans website. Smart dude, electronics engineer or something.

Moparmans website is down right now, so cant link article. Can search. “w-t mod simplified”. Pcm protection is a good one too.

Basically. Moves alternator + to passsenger battery with breaker protection. Grabs all the grounds from the front engine harness and splices them together on timing cover to remove ac inductive noise into ground.

Ground system not great with these rigs to start with. Pcm to passenger - has connector that can be spliced hard wired. Replace fender/body with 8awg. No frame ground that side. Main neg near turbo drain to clean check.

Drivers battery, new 8awg body, 4 awg to only frame ground near steering box bolts. Main - goes to bottom timing cover.

The only positive + to check is drivers battery to fuse box, and the fuse thats there. Clean and check.

Theres other grounds that connect thru out frame and body, but if you start with making the batteries good that should be a large improvement. OHM meter will be your friend. Leave an aligator clip on batt neg, and long extension to back of cab on good clean metal back there non paint. See how much resistance is there before and after.
 
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#5 ·
Use the search bar above. The FSM is also downloadable on this site. All good information. Next, as mentioned it's probably a ground issue.
Also according to the manual, the brake light switch is a one time usable deal. Use it once and it's set. Not sure how or why on that.
 
#6 ·
After cleaning and checking every ground on that truck I finally noticed something. I bumped a turn signal with the key off and lost the 4 volts I had in the rear on the side that the turn signal was on which made me think of the 4 way flashers. I hit that button a few times and the brake lights came back so all it was was a sticky switch in there. Bout a nuff to drive a man in sain but it's fixed.

As far as the brake switches being one use only im not sure that I believe that's because I am running a switch out of a junk yard truck so may just be something that dodge says just to make us spend more money
 
#7 ·
Ive had some success at reusing brake light switches, but seems to only buy time before I get a new one. I think theyre around 20$ so its not too bad. Whats annoying is when theres a hydro boost or master problem, almost always requires a new switch once repairs done.

Glad you figured out the problem.
 
#8 ·
That is afterburn with the ground fetish. But it does sound ground related, partly, can never hurt to check them for resistance or shorts.. I suspect the the multifunction switch is shorted out or the pins in the internal connections of the trailer plug is corroded and shorting out between circuits.
 
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