strange rear brake light/brake light switch problem, I LOVE electrical gremlins...

[jocko]

So, my truck had an ancient electrical trailer brake adjuster wired into the brake light switch circuitry - problem was that the only time my rear brake lights would actually come on was momentarily during pedal depression and again during pedal release. Hmm, weird. I don't plan on trailering, so just to get this thing safely on the road with functional brake lights, I eliminated the trailer brake bias box. Now the orange and white wires connect directly to the brake switch. I've checked clearances, pedal depression in fact releases the switch as it should and I've also checked the switch - infinite resistance with the pedal released, zero when pressed, so seems the switch is good to go also.

Interested in your thoughts as to what might be the problem. PO has a no-kidding rat's nest of wiring crap all over the truck. I'm gonna go stare at it awhile and scratch my head a bit longer, but wanted to see if anyone's ever had a similar problem (and, more importantly, what the solution is).

Probably going to run and grab a new switch just in case, even though it checked good, but just want to eliminate any funny bizness. But I think I've completely eliminated any input from the trailer brake setup by removing the box and wiring the original wires direct to the switch. Hmm.... Thanks in advance.

[Rufton]

My intermittent tail light problem turned out to be ground. The bed sometimes lost ground w/ frame. I used existing holes and ran a grounding strap from frame to bed. Your problem sounds like pedal rubbing against a wire but gremlins can be sneaky.

[jocko]

thx rufton, I know what you mean about grounds - have chased them painfully on other trucks. This seems to be a little more predictable - rear brake lights work, but they only flicker on during initial pedal depression (i.e. when holding the brake pedal down, they aren't on after they flicker on for a second) and then they flicker back on/off when I release the pedal. Just got the switch, gonna try that, but I don't think it's the problem. Thanks, I will look into the ground possibility. Such a rat's nest, hard to tell what he has tied into everything. One thing I notice dis there is a hot splice into the white wire to the switch that is not original, may temporarily eliminate that to see if it helps.

[68gmsee]

A helper would really nice about this time. If you're married, ask your wife. Mine gripes when I ask her to help but she still helps me.

Before you start trouble shooting:

As Rufton mentioned, install ground straps all over your truck. I bought new battery cables and four ground straps: bed to frame, frame to cab, cab to engine, radiator support to frame. I got rid of a lot of brake light gremlins including battery gauge not working.

Then if it still acts up just put a meter or test light on the brake light sockets and check for voltage.

[cdowns]

gremlins rock

[jocko]

Originally Posted by 68gmsee

A helper would really nice about this time. If you're married, ask your wife. Mine gripes when I ask her to help but she still helps me.

Before you start trouble shooting:

As Rufton mentioned, install ground straps all over your truck. I bought new battery cables and four ground straps: bed to frame, frame to cab, cab to engine, radiator support to frame. I got rid of a lot of brake light gremlins including battery gauge not working.

Then if it still acts up just put a meter or test light on the brake light sockets and check for voltage.

Almost worth getting married again... but it's cheaper to mount a convex mirror on the wall behind the truck. Strangely, the problem WAS the switch. Even with it out, it was still checking good, but just something weird goin on there. Oh well, mystery solved. Glad I opted to change the switch on a hunch just to eliminate it for sure. Maybe will help someone else.

[dazza]

Originally Posted by jocko

Maybe will help someone else.

Indeed helpful, in more ways than one. Had a good laugh...

Originally Posted by jocko

Almost worth getting married again... but it's cheaper to mount a convex mirror on the wall behind the truck.

Haven't been married yet, and it's these little things that seem to grow that "hunch just to eliminate it for sure."

[jocko]

Ha! I'm just kidding! Marriage was great, every single time!

[dazza]

yea, most times when reading posts like this, it's kind of like a Jerry Springer or Heraldo show, in that I can live vicariously through the person posting, have a quick laugh or two, crack open a beer, then tell my 41 year old short n' wide girlfriend I'm going to give her a bath... right out in the driveway for everyone to see! Never a negative response and always happy to take me out for a drink afterwards!

[Ol Blue K20]

all my wives were great house keepers each one kept the house
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[Sklptrljay]

If it's lighting up for a moment, then going out, that says to me the voltage is finding a less obstructive path to ground.

SOMETHING is drawing the voltage from the same circuit when you press the brake.

I would start by making sure everything is grounded properly as that could definitely be an issue also, if it can't make a good return path for the voltage.

If that doesn't do it then you'll have to trace the brake wires and see if it's connected to a load somewhere else.

You can figure out if there is a load by using an amp probe on the brake wire when the pedal is depressed. If the load continues to be present after the brake light goes out, then you know power is being supplied to some device. if it goes to zero then it is probably a bad ground.

A test light could work also. When you put it in series with the brake wire and hit the brake if it comes on and goes out it is probably the ground, if it stays on it's probably a device draining the voltage.

Hope this helps, auto electrical is witchcraft, good luck.