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Old 07-09-2019, 09:27 AM   #1
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Yay, another brake light / hazard light thread

Hey folks. I have a 1994 Damon on an F53 chassis. I have no brake lights and hazards. Googling of course brings up this discussion a million times, but I haven't seen anybody mention some of my symptoms so I figured I would add yet another thread on this (sorry :( )


So first off, I do know exactly when it started. I had my RV in my driveway to work on it before ever driving it and had just backed it up to where I keep it. I got out with it still running and decided I needed to go another foot, but when I got back in to move it, I could no longer shift it out of park. Google explained that to me and told me how to cheat around it.


Since I had other lighting issues, I decided that a new multifunction switch would be a good start. I installed it and still no joy. Same symptoms. I was going to start messing with the wiring harness etc to look for a break but never got to it. A couple of weeks later I was warming up the RV while doing something else, and I suddenly heard the hazards flashing. I messed with the tilt, tugged wires and slapped a few things around and I could not make it stop working.



Too many other things to fix so I just moved on. Fast forward again to this weekend where I have the RV plated and take it on its inaugural trip about 50 miles away. During this trip, the brake warning light came on. Lifted the e-brake pedal (while holding the release) but that didn't make the light go off. When I got to my destination, I checked the master cylinder and it's still full. The brake/gear interlock still functioned properly while I was there, so I assumed I still had brake lights. Had no reason to check hazards.



When I left the next day, I still had brake interlock function and the warning light had gone out. Stopped shortly into the trip and the interlock still functioned. Stopped for gas and it no longer functioned, so I assume somewhere in there the brake lights quit again. Brake warning light came back on about 20 miles later.


So back at home the next day I started testing. The brake warning light is not on at this time. Turn signals have functioned properly throughout this. I looked at the back and front lights, and with the turn signals on they perform properly. No sign of lights finding their own ground through the other lights (like you would see with a bad ground). Tried unplugging the brake pressure switch at the master cylinder to see if that caused any change, and no luck.



At the fuse (#9 I think?) it measures 12V on both ends (not blown) when I am doing nothing. But this is where it gets weird. If I activate the hazard lights, this voltage changes to 3V at either side, no flashers, no clicking and no lights (not even dim / not flashing). If I shut the hazards off and step on the brake, the voltage on both ends of the fuse goes to 0V. I have tried fiddling with the tilt wheel to see if I got intermittent success but no luck. Tried tugging on the wires at the multifunction switch, again with no luck. I even unplugged the shift interlock solenoid to see if this would help, and again no luck.



So I am assuming that since the voltage drops wien I try to use the circuit, there is a short between something or even to ground. But where would it be? If it was in the lights or their harness, wouldn't that affect the turn signals as well? The flasher itself seems to function, since it clicks along fine with the turn signal. And the multifunction switch was replaced with no change. Add in that the whole thing randomly worked again for a while with no input at the time.


Any suggestions?
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Old 07-09-2019, 10:47 AM   #2
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Voltage drop at the fuse when load is added would indicate a poor connection on the supply side .
Your testing with a VM ; remember that it only takes mili-amps to get a volt reading . Try a 12 volt test light .
I'm not sure where that circuit gets it's power , but older Dodge vehicles had flasher fuse power direct from the positive battery terminal ; so look there for a small wire with corrosion issues.
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Old 07-09-2019, 01:02 PM   #3
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Does the head lights work with the hazards on?
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Old 07-10-2019, 10:50 AM   #4
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Quote:
Originally Posted by Skip426 View Post
Voltage drop at the fuse when load is added would indicate a poor connection on the supply side .
Your testing with a VM ; remember that it only takes mili-amps to get a volt reading . Try a 12 volt test light .
I'm not sure where that circuit gets it's power , but older Dodge vehicles had flasher fuse power direct from the positive battery terminal ; so look there for a small wire with corrosion issues.

That supply side error sounds like something to definitely have a look at. Maybe I will feed a new source to the circuit (with a fuse of course) to see if that solves my problem. I did some poking with a test light a couple of weeks back. I tested every fuse in the bus and had power to both sides of all of them. Don't think I probed the fuse with the test light while trying the signals and brake, but I do remember being able to 'complete' the circuit and make the flasher go when I probed the load side of the flasher. I seem to remember the brake switch having no power at either terminal, but I can't say for sure if the flasher was on at the time to break the circuit or not.


Quote:
Originally Posted by subford View Post
Does the head lights work with the hazards on?
I can't say for 100% certain, but I believe they do. The headlights had their own issues with someone wiring one of the headlights wrong (low beam and ground wire swapped) but I think I have that solved. Also they had taken the low beam wire and soldered it right to the headlight on both of the inboard headlights. No idea why someone would do this...
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Old 07-10-2019, 02:59 PM   #5
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Fuse #Q supplies the power to the head lights, fuse #9 and fuse #5.





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Old 07-10-2019, 06:47 PM   #6
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Soooooo. Good news / bad news. Good news is that I determined that the fault is right at the fuse itself. The terminals on the fuse and in the box are so corroded, it makes its own high resistance. The bad news is that I broke the circuit side (green red) wire off the terminal while trying to clean it. I guess I am running to a full time hot and putting an inline fuse to solve my problem.

Thanks for the help, guys. Off to the next problem.
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