Depressing brake pedal causes K5 to shut off

[shamb1s]

90 K5, 5.7L TBI, Original motor and trans.

On my way to work my K5 completely shut off on me as I was coming to a full stop at my Air Force base entrance gate. It happened exactly as I depressed the brake pedal. Everything shut off as if the ignition had been turned off. I pushed the K5 about 30 feet forward to unblock the gate and when I jumped in to stop it and pressed the brake pedal, the blower motor, dash lights, and radio all came to life again. I immediately turned the ignition and it started right up, so I made a mad dash to my work center. On the only turn on my trip there I again pressed the brake pedal and the truck died again as before. I pulled off to the side, put it in park and continuously depressed and released the brake pedal for about a minute to see if the power would come back but it didn't. Luckily I was only a block from my work center. Came back to it about an hour later with a buddy to tow it to my parking lot and it started up again. It's now safely parked in a parking lot but I didn't have time to tear into it today. I'm hoping I can get some ideas on what the problem could be before I drive back to work and troubleshoot in the parking lot. Any advise or insight you guys might have would be greatly appreciated.

TL;DR
Pressing brake pedal causes complete electrical power loss, pressing brake pedal again will sometimes cause power to come back.

 

[Kain]

ground short

 

[shamb1s]

Shouldn't a ground short cause fuses to blow in the associated circuits? And once they've blown those circuits shouldn't be a problem anymore correct?

 

[4xcrazy]

Only time I ever had mine shut off like that with the brakes, was when the battery was dead due to a bad alternator, not enough charge in the battery to run the electronics with you hit the brakes and the taillights turn on. Just barely enough to run the truck though, was weird.

 

[Kain]

There is no fuse on brake lights, at least that's how my trans am was when the brown wire that runs to the brakes caught fire at 65 on the freeway

Sent from my VM670 using Tapatalk 2

 

[blazer74]

Check your fuse panel and feedthru, something could be loose.

 

[Kain]

Also did you work on it recently

 

[shamb1s]

I put a new battery in about 4 months ago, and that was the last time I worked on her. Thanks for all the replies, I'm going to try and work on her tomorrow if the temperature is above 20F

 

[Kain]

ya i got to change a u joint and it snowed here 4 inches so it will wait,
glad it the front shaft

 

[eagle mark]

This is a strange issue for sure! I'd be looking for wires dangling and hitting the brake pedal arm.

If it were a short, well it would/should blow a fuse or not come back... you hit brake and it coming back makes me think something is rubbing the brake pedal arm?

 

[shamb1s]

I haven't had a chance to work the truck yet, its been -10F here, but I will be sure to track my progress here for historical record.

 

[diesel4me]

I'd guess it might be the wiring harness has rubbed against the brake pedal arm and your touching the main red wire going to the ignition switch to ground..that "should" blow the fusible link eventually I'd think though,either the ones at the starter or the one on the firewall neat the brake booster,that has a plastic isolator block with a fusible link wire on it..maybe it doesn't stay grounded long enough to melt the fusible links?..

I had a truck that would stall when you applied the brakes,but it turned out the brake booster had a ruptured diaphram and would leak enough vacuum to kill the motor when the brakes were applied!..that was a fun week--driving a manual tranny truck with NO power assist,and wanted to die when you applied the brakes..made taking off on an uphill grade dam near impossible!..had to drive it that way a week till I could get a salvage yard booster to install on it...

 

[Big6ft6]

also, this might sound dumb but double check your battery connection. I've (more than once) had a battery cable loose because I finger tightened it during some work and forgot to go back and tighten it down. Everything will be great driving and everything, but suddenly with the right surge of power demand (in your case brake lights) something about the tiny contact area of the loose cable to the battery "pops" and it is like the battery is completely disconnected, just like a fuse blew, everything is dead. Just take a second to double check your battery cable are nice and tight.

 

[diesel4me]

Yeah,I had that happen once when I "threw" in a good side post battery to drive a newly purchased used truck home,and the bolt that holds the positive cable on bottomed out in the hole before tightening against the cable good--first stop sign down the road a ways,I decided to turn the headlamps on,it was getting dark out---...

As soon as I pulled out the switch ,the truck died,and when I tried to re-start it--all I got was the dreaded "click-click-click" chatter of the starter solenoid!--then NOTHING!....thought sure the battery was junk!...luckily I was able to get it to start by twisting the cable up and down and it made contact enough to fire up again...last thing I needed was to be stuck there with my plates "attached" from my truck ,trying to sneak the truck home!..made it home OK though...