Strange electrical problems

[garywcox]

1997 Pontiac Grand Prix 2.8 ltr v6 engine. 104,000 miles.

The problem started out where the air conditioning/heating blower motor would cut off for a few seconds and then back on. It started to become progressivly worse happening more often and for longer duration.

Also when the blower motor cut off the led for the airconditioning would also go off as well as the led for the rear window defogger. The running lights would also go off. Also when this electrical outage occurred if the headlights were turned on by the automatic daylight sensor they would turn off but if I manually had the headlights on by the manual headlight switch the headlights would stay on.

The radio and engine were not effected by the electrical outages. I could also hear a click in the dashboard when the electrical outage would occur and a click when it would come back on as if a relay was tripping.

The problem has progressed to where 95% of the time that the airconditioning/heater blower motor and the above mentioned electrical systems do not function at all if I have the blower set on speeds 1-4. If I set the blower to speed 5 the blower consistantly works as well as all electrical systems. As soon as I turn the blower to setting 1, 2, 3 or 4 the blower moter turns off, I hear a click in the dashboard, the running lights turn off, rear window defogger does not work and the airconditioning light goes off (the airconditioning compressor also cuts off). As soon as I turn the blower switch to off or to posisition 5 everything comes back on except in off posisition when the blower does not normally run but the rest of the effected electrical systems are operating.

The dealer checked the computer and it did not have any codes for any problem. The battery has been replaced.

Gigling the blower switch or switching it between speeds 1-4 does not effect the problem as the effected electrical systems will remain dead.

While this may or may not be related the gas gauge does not consistantly work. Often it will show all the way full no matter how much gas is in the tank. Sometimes it will show the correct amount of gas but when it isn't working it always shows full.

As I mentioned the Radio and engine has never been effected by the electrical outages.

It sounds like to me like a protection circuit activating like a circuit breaker and that the running lights, blower motor, rear window defogger and airconditioning are on the same circuit?

Perhaps it is a short or a grounding problem? I'm not a mechanic, I'm a computer tech so I'm not sure where to check for electrical connections or grounds if that is what I should be checking for?

Any ideas would be appreciated as no one else has any? The common element is the effected electrical systems with the blower switch being the catalyst that causes it all.

[empathydude]

sounds like grounding, if you say when you turn it to full blast it works fine, then maybe at full its a 12v circut and everything else it grounding through the blower. the ground wires for the ac control console are behind the dash, so it the blower ground but they are both incredibly hard to get to... at least for those who don't like looking at the guts of their car.

[garywcox]

I assume the grounding wires I need to check are accessible from inside the car by pulling out the dashboard?

... Gary

[empathydude]

Originally Posted by garywcox

I assume the grounding wires I need to check are accessible from inside the car by pulling out the dashboard?

... Gary

behind the dashboard is an understatement =) they are against the firewall...

[garywcox]

Originally Posted by empathydude

behind the dashboard is an understatement =) they are against the firewall...

Actually it turned out to be the ignition switch. It's been replaced and everything is working fine except for the gas gauge which I think is a separate problem.

... Gary

[BIG-L]

Im sure that the ignition switch harness is what they replaced as thats a problem with our cars....best way for it not to happen again is to always make sure that the heater switch is turned off before starting the car....the voltage spike is hard on the contacts at start up and can also mess other things up as you have found out.Thats what im trying to tell this member in this thread........~Larry~

http://www.automotiveforums.com/vbul...72#post2082872