60jerry

Gentlemen, I've been fighting a problem for about a year and haven't licked it yet. I have a '98 GMC Sonoma standard cap, 4X2 pickup with a 2.2L, AT, A/C. I got it from my bother who bought it new. He mentioned to me that the brake lights stick on now and then. Well------he's correct. I've experience this several times. He had replaced the brake light switch with no change. After several dead batteries from the brake lights staying on I got a manual and decided to try the cheapest thing first. Since the four-way flashers acted strange when the brake lights were stuck on, I replaced the hazard switch. No change. Then I got a multifunction switch (AC Delco part) and put it in. No change. Now what the heck is going on here? I've noticed that the brake lights will stick on after the vehicle has been operated for a while in warmer weather. At this point is seems the problem occurs more readily when the inside gets warm or perhaps when the MF (multifunction) switch is hot. I've been able to pull the brake light fuse underhood and the brake lights go out and a bit later (half hour, perhaps) reinstalling the fuse does not bring the brake lights on unless the brake pedal is depressed. All is back to "normal". I'm perplexed that there isn't more mentioned somewhere about a fix for the problem. It seems to me that the multifunction switch is built to such close tolerances that when the part gets warm the internal contacts get close enough to make what some call a "short circuit". It is not necessarily a "short" so much as an unintended connection. OK, "short" is an OK way to describe it. Anybody have another idea, since I've replaced all the involved parts? I ain't one of those guys who replaces parts 'til the problem goes away, so don't get that idea. I want to diagnose it first and replace what's needed. I've tried to figger this out and found the factory manual to be less than helpful because the circuits are all separated so one cannot get a feel for what circuit is close to another circuit. This brings up another subject. Anyone else think that the factory manual is a bit "busy" or overly involved?

I know I'm wordy, but many years of working on vehicle emissions and electrical issues makes one kinda weird (strange).

Damn, I hope someone has an idea, 'cause I really like this truck. Good gas mileage and it'll haul anything I want. I'm a custom car guy, so not much heavy stuff is hauled. I like to customize older Chevys just for fun.
Jerry in Denver, CO