Red Brake light stuck on 74 K5

[gooch]

Brakes work great ? Just bought it used , previous owner unpluged wire that goes under center radiator area ? What is that ? On frame between steering and radiator , Is it safe to leave it unplugged ? Unplugged NO LIGHT in dash , plug it in RED LIGHT IN DASH . Its a 1974 K5
THANKS FOR HELP !!!

 

[gooch]

Been reading , its a comb valve , it regulates how muck brake fluid goes to rear and front brakes . Not sure if I have a leak or not ? Going to check system this week . Just bought it , and it was almost out of brake fluid . I read there is a reset button , so I am going to reset button 1st . Then go though brakes when I lift kit goes .

 

[diesel4me]

That switch they unplugged turns on the brake warning lamp in the dash when the proportioning valve (PV) detects an imbalance in the pressure of the front and rear brake lines,which means one has a leak or air trapped in it ..

You will have to try bleeding the brakes to get the light to go out,after plugging the wire back on the switch...for the record,I was never able to get the light to go off and stay off in my 82 GMC,even when I tried bleeding the lines right at the PV..it would only go off until I pumped the brake pedal again...so..its been unplugged for about 10 years....

The brakes work fine,I just cant seem to get the valve to re-set to shut the light off..when I got the truck, I found the bulb and little holder it goes in,in the ash tray,so I guess the previous owner failed at getting the light to stay off too..I had to put it back in to get a inspection sticker,luckily I convinced the guy it was only lit up because the e-brake wouldn't release fully...he then told me "I'd just unplug that wire if I were you"...with a wink!..its good to know someone who gives stickers that isn't totally anal..

 

[gooch]

Well ..........
All new brakes , calipers , stainless brake lines , master cylinder , all new on rear backing plates , all new parking brake cables , so I HOPE the light will STAY off . Still working on it , so we have NOT done a bleed yet .

 

[diesel4me]

I never bothered to look for another proportioning valve,they are the same on many years of GM cars and pickups...from about 1971 to 1987 the trucks used the same ones,the 71 and 72 had them mounted on a bracket near the master cylinder instead of on the front crossmember like the 73-87's had them...

Most of the GM cars & trucks from that era were the same valve also,with a few exceptions..unfortunately everything that old around here was crushed decades ago,or the few stragglers that do show up in boneyards are usually stripped bare already--or so badly rusted nothing of much value can be used off them..they stay in the yard a week to a month,then get squashed,if not right away--I know of one salvage yard that still has a few older trucks,but its unlikely the PV is still on them,or any good..dont feel like opening up my brake system and having to bleed it all again....I figured I'd just leave mine alone as long as the brakes work OK..

This truck was the only one I couldn't get the brake light to stay off on out of many I've owned--I did have to replace a few PV when I tried messing with the "pin" your told to push in or hold out if you cant get the front brakes to bleed in service manuals..they were working fine till I messed with that pin,then they leaked!....I've bled a hundred other vehicles brakes OK without having to touch that pin...so I'd not touch it if I were you..