I just got done reading the "Brake" forums... Nothing. So im here.

I have an '88 F150 and I have noticed that the red brake light on the dash will come on for varying amounts of time. This happens during driving. ABS light has been on for the last few years... Thats not important to me. I checked my brakes yesterday. I have 50% on front and 80% on rear. Master cylinder was replaced recently and I never put the sensor back in it. Brake fluid level is up to MAX . No visible leaks.

So my question is..is this idiot light just being that?

Oh yeah.. And I dont use my E-brake at all whatsoever.

 

The switch on the E-brake lever grounds the voltage from the idiot light. Remove the connector from the switch & if the light goes out the switch needs replaced or adjusted.

BTW, i would'nt waste my time & money on fixing the ABS nonsense either.

 

Awesome, thanks. Yeah, this truck is too primitive for any of that high tech brake garbage. I dont need an idiot light telling me im an idiot. Id rather not pull the bulb but if it comes to it I will. Ill unhook the E-brake from the switch or whatever and see where that gets me.

 

I would check the parking brake switch. On my 85 the spring for the parking brake was weak and let the pedal hang just low enough to trip the sensor. The light can also indicate an out of adjustment proportioning valve.

 

Why do you ask why the truck is telling you you have no brake fluid when you didn't bother to reinstall the low fluid warning switch?

 

Because I also said I replaced the master cylinder a while ago and never switched the sensor over and brake fluid is up to MAX. I thought people would read this and go "Ok, so the master cylinder is good, brake fluid is up, and apparently the light hasnt been coming on until recently".

I know that light is for more than the brake fluid. And it hasnt been coming on except for a few flashes about 2 months ago when I was pulling a trailer that weighed more than the truck did for 1000 miles, and recently it started dimming and brightening with the throttle.

It was off yesterday so ill see if it stays off. When it decides it wants to come back on ill pull the wire for the e-brake.

 

If the light is intermittent there is also the possibility that the plug going into the master cylinder is shorting internally or one of the connections inside it is going bad.
I know that I had that problem at one time.

If it varies with RPM (alternator output) I'd be looking for a short or ground issue.

 

Ill check that out and tape up the plug just in case.

 

Hey, ok it has been a while since ive been around this problem. BUT! I think I got it fixed. The problem stopped for a while after this was posted and ArdWrknTrk was on to something. So, my truck was being all weird where when im driving there wasnt a problem but when I came to a stop all the lights dimmed down, the volt gauge dropped to 11 and with my turn signal on everything in the dash flashed slightly. When I drove, it went to 14 and all was well until I stopped again.

My brake light came on and stayed on and it was really irritating me. I had the parking brake plug unhooked, I have no sensor in the master cylinder anymore so it was dumbfounding me. I was hunting around and found the plug for the brake fluid sensor WAS touching the brake lines coming out of the reservoir. I taped them up separately with electric tape and the light was off, havent seen it since.

Also, my voltage stuff has not happened. Could this have caused the 'output' problem or whatever? Or is it just coincidence? I figure if it was grounding out, maybe. Otherwise im going to come to the conclusion my alternator is slowly dying out.

Besides the above question, I thank everyone that helped with this problem, and sorry I took so long to do something about it. I tend to be a slacker. But, this thread it closed! Ha. Thanks again!