Intermittent Main Brake Lights - High Mount Always OK

[slovcan]

Hi folks,

Maybe 8 years ago my main brake lights went intermittent, then magically were fine until last year. Back then the truck (1997 K2500) only got used once a month or less. I figured steadier use cleared up the problem. Back then I was told it was probably the multi-function switch - classic symptom they said.

When it happened last year I bought a new multi-function switch (WVE from Rock Auto) and that fixed it. The switch even FELT smoother and higher quality than the original. A month or so ago I had the interior cleaned, shampooed and shined up. After that the main brake lights failed again - high mount still OK. Then I noticed the hazards were flaky. The switch felt like it had some drag and if I fiddled with it a bit the hazards would work. AHA, I thought, some cleaning crap got into the multi-function switch so I sprayed some electrical contact cleaner into it around the hazard switch.

Rock Auto replaced the switch under warranty despite my suspicions of what happened. I had to pay the return shipping and the labour to get it changed, of course. When the guy (my regular repair guy for stuff I don't want to do myself) backed it out of the garage I saw the main brake lights didn't work again - or so I thought - the high mount did work. But when I checked right after that they were fine and stayed fine - until yesterday.

I saw they were out again so I fiddled with the bloody multi-function switch, but that didn't help UNTIL I selected high beam and back down to low beam. Now all is well again. Except I don't trust it.

Did they send me a bad switch? Is the WVE brand a poor quality brand? Should I just buy the most expensive one they sell?

Thanks,
Glenn

 

[thegawd]

I dont think the multifunction switch has anything to do with the brake lights. you may just have a bad ground. theres one for basically all the dash electronics and it's near the obd2 plug.

 

[slovcan]

I dont think the multifunction switch has anything to do with the brake lights. you may just have a bad ground. theres one for basically all the dash electronics and it's near the obd2 plug.

Thanks gawd, I'll check.

 

[mockspeed88]

The ground on the back of the block passenger side. Mine wouldnt work only the top one. Found out my ground was bad on the block. It got pulled off when I installed my transmission

 

[slovcan]

You know guys, I have the FSM, but it is not a great copy. However, it does not show the multi-function switch or the high mount brake light. It does show a wire from each Tail/Turn/Brake socket going to the turn signal switch (which IS the multi-function switch). It also doesn't show the actual brake light switch, but it does NOT show the wire from the Tail/Turn/Brake socket going to a brake light switch.

I'm going to go with my original thought - which was initially given me by a trusted GSE mechanic at my former airline - that the multi-function switch decides which signal to send to the Tail/Turn/Brake sockets, turn signal, hazard light signal or brake light signal. If I could see a proper schematic, I bet I would find a wire from the brake light switch directly to the high mount brake light that likely splits off to the multi-function switch.

In fact, if I remember right, that mechanic gave me a schematic at the time (many years ago). God knows if I'll ever find it.

What I DO know is replacing the multi-function switch did fix the "no main brake lights" problem. Then, when that switch got buggered by the detailing goop, the main brake lights were lost again. Replacing that switch once more gave me back the brake lights. The first time the truck was moved after the second switch was installed, the main brake lights STILL didn't work, but did on the second application and have continued to work for the past couple of months. Except for ONE time when I was changing the radio (I know, no connection, but there it is). Anyway, I selected high beam and back to low beam and the main brake lights were again working and haven't failed since. I'll call it a fluke - maybe owing to a slight difference in quality between the WVE switch versus the original GM/AC Delco one.

Cheers,
Glenn

 

[stutaeng]

You know guys, I have the FSM, but it is not a great copy. However, it does not show the multi-function switch or the high mount brake light. It does show a wire from each Tail/Turn/Brake socket going to the turn signal switch (which IS the multi-function switch). It also doesn't show the actual brake light switch, but it does NOT show the wire from the Tail/Turn/Brake socket going to a brake light switch.

I'm going to go with my original thought - which was initially given me by a trusted GSE mechanic at my former airline - that the multi-function switch decides which signal to send to the Tail/Turn/Brake sockets, turn signal, hazard light signal or brake light signal. If I could see a proper schematic, I bet I would find a wire from the brake light switch directly to the high mount brake light that likely splits off to the multi-function switch.

In fact, if I remember right, that mechanic gave me a schematic at the time (many years ago). God knows if I'll ever find it.

What I DO know is replacing the multi-function switch did fix the "no main brake lights" problem. Then, when that switch got buggered by the detailing goop, the main brake lights were lost again. Replacing that switch once more gave me back the brake lights. The first time the truck was moved after the second switch was installed, the main brake lights STILL didn't work, but did on the second application and have continued to work for the past couple of months. Except for ONE time when I was changing the radio (I know, no connection, but there it is). Anyway, I selected high beam and back to low beam and the main brake lights were again working and haven't failed since. I'll call it a fluke - maybe owing to a slight difference in quality between the WVE switch versus the original GM/AC Delco one.

Cheers,
Glenn

Yes, rear brake tail lights are wired through the multi function switch, pedal brake light switch and relay. The brake cab light comes directly through the brake light switch. That one doesn't go through the multi function switch.

 

[slovcan]

Yes, rear brake tail lights are wired through the multi function switch, pedal brake light switch and relay. The brake cab light comes directly through the brake light switch. That one doesn't go through the multi function switch.

BANG! There it is. Thank you, Stu!