thats right, i hit the defrost button, car shorts out and dies... before i start chasing wires, has anyone had a problem like this?

 

i have a similar problem... car keeps running but everything electrical (gauges, lights, stereo) shut off. haven't started tracking it down 'coz there's so much other stuff i need to do. :P

 

my defroster didn't work years ago when i got the car, so i pulled the switch apart and found a trace on the board had burnt up. so i solder a wire on to replace the trace. then when i tried it, it did what your talking about. with the car running i hit the on switch and the car died.


i unhooked it and never got around to fixing it. i guessed a wire at the rear hatch shocks had shorted to ground but never worked on it.


good luck, post up if you figure it out...even thou i've since used the switch as my nos arming swtich. i've always wondered what caused that.

 

Very common type of problem.

It's not a "short" (an unintended connection between 2 things that aren't supposed to be connected); rather, it's a HIGH RESISTANCE (bad connection) somewhere in the circuits that feed power to BOTH the ignition switch and the defogger. With that, when you turn on the defogger and it draws its VERY high current, there gets to be so much voltage drop at the bad connection, that other things stop working.

Typical places for a bad connection would include the fusible links at the starter, the bulkhead connector, and the splices where the big red wires that feed various things all come together. Shouldn't be too hard to spot; since a bad connection generates heat, the bad spot is probably visibly charred looking.

You can find it with a voltmeter.... just turn the defogger on, and trace the circuit all the way along the path, starting at the battery, measuring the voltage at each convenient point. The car doesn't have to be running. You might see (as an example) 12.5V at the battery, 12.4V at the big red wire after the fusible link, 12.3V at the firewall side of the bulkhead connector, and 8.1V at the pass compartment side of the bulkhead connector. Guess where the problem is if you see that.

 

i still have not had time to look car over, but today my battery died while driving, and i put a ne one in and same issue, i looked at altenator post, and it was charred badly. im hoping that this is un related and the altenator just went bad. if i cannot find a problem area, could i just pull the fuse and not worry about it?

also i just remembered that sometimes my heater fan works how it wants to sometimes high is high, sometimes it dont come on... o well time to start the trouble shooting

 

Another bad connection...

That one is EXTREMELY common; like, EVERY GM car that has this same system, eventually does it. Not just Camaros and Firebirds.

Find your blower motor high-speed relay: if you follow the purple wire back from the blower motor itself (on the firewall right next to the pass side fender) you'll find that it goes to a little box with a plug, that's the relay. One of the wires going to the relay will be a big fat red one. Follow THAT wire: it will go up, above the engine at the lip of the windshield cowl, almost to the level of the hood. About over the right valve cover, you will come to a plug. Unplug that plug and enjoy the sight of a connector burnt to ash. Get yourself a set of the BIG HEAVY DUTY yellow slide terminals; the big, fat, heavy kind, not the regular weenie ones that are the same as the red and blue sizes except with the yellow barrel, but the BIG HEAVY DUTY ones. Cut the stupid factory connector off and throw it away and replace it with the one you just got.

Incidentally, while you're troubleshooting smoked electrical connections, the NEXT one that will bite you, is the one that feeds power to the AC control head. Remove that from the dash; find the electric "mode" switch, which will have a plug whose wires include a green one (AC compressor), one that goes to the fan switch whose color I don't recall, and a brown one (the power feed). Follow the brown wire about 15 - 18" up into the dash. You will come to a plug very similar in design to that stupid one under the hood, which (surprise!) fails in exactly the same way. When it goes bad, the entire HVAC system stops working; no fan at all, no AC. Replace it as well. I've changed that one out in at least 8 GM cars belonging to members of my immediate family over the years.

Yes the alt being toasted that way can cause all manner of electrical strangeness to occur. The defroster did not "damage" the alt or "cause" the problem; its behavior is merely an INDICATOR of some other existing problem. Which could possibly be the fornicated alternator.

 

thanks for the info, ill start chasing wires, also i removed th a/c when i put the new motor in... do i need to do something to the connectors that used to plug into the compressor? as for now they are just taped up so no water can come in.. thanks

 

OK I am digging this out because my 85 is doing the exact same thing. There wasnt any follow up as to what fixed it. I was able to crawl under the car and checked the fusible links and it appears they have been rubbing on the metal and bare wire is showing. I will get this fixed ASAP but was wondering what else could be wrong. With the key on engine off, I hit the defrost and the dome light dims.

 

I just changed my hatch struts and realized that the wires for my rear defogger have lost all their shielding ( it just feel off) and was tring to find some help on here and found this post and thought it might be something you guys might wanna check.