On my 88GT, when I push the button for the defroster, the engine will immediately bog down and the alternator belt will start squealing, like there is a tremdous load on it. Nothing happens to change this state of the engine if I push the button again, and I have to turn off the engine/ignition to make this stop. When I start it up again, the issue is resolved and everything is good again.

This seems like a direct short to ground. Question is, wheredo i begin? I have already tried another switch, same issue.. What else is in this circuit?

Help!

quote phils88GT: What else is in this circuit?

Do you have the '88 manual?

From the Manual

quote With the Ignition in RUN, voltage is applied to the Defogger Control. When the Defogger Control Switch is pressed ON, voltage is then applied to the Defogger Timer-Relay. The contact closes, which provides voltage to the ON Indicator and the Rear Defogger. The contact in the Defogger Timer-Relay will stay close until the Defogger Control Switch is OFF, or until the timer cycle is complete.

So, if you cannot turn the Defogger Control Switch OFF, maybe check the Defogger Timer-Relay...........?

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Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

All I have is the 88 Haynes manual for my car. I don't know where the relay is located. Is it in the fuse panel or elsewhere in the car?

quote Originally posted by phils88GT: On my 88GT, when I push the button for the defroster, the engine will immediately bog down and the alternator belt will start squealing, like there is a tremdous load on it.

So nothing else appears to put a "tremdous load" on the alternator... even if everything (headlights, high beam, A/C blower on full etc) is turned on at once (except for the rear window defroster)?

Nope! I can run everything else (AC doesn't work), lights, heater, etc. and no strain on the alternator. But if I hit the button for the defroster, the engine will almost stall, the alt belt will squeal badly, until I hit the button again to turn it off. The LED doesn't even come on on the defroster switch when I cut it on! I probably ought to mention that one time last week, it did actually work without doing this, but it didn't stay working for long.

The biggest question for me is... how often do you actually need to use the rear window defroster in South Carolina?

My Formula was originally from Knoxville Tennessee, and wasn't equipped with a rear window defroster. However, even up here in the Great White North, where we all live in igloos , the lack of a rear window defroster has never been an issue.

Well, probably never.. I am just concerned more that it is doing that... I worry that I could have a potential fire hazard.. I don't want that.. Where is this delay relay for this?

quote Originally posted by phils88GT: Where is this delay relay for this?

From Here...

May not be problem w/ Defog...

The "relay" is a small box under the dash on right side of "frame" holding the steering column & brake pedal.

Defog has 2 "fuses"
Gauge Fuse that runs timer section, should be 5 & 2.5 minutes On.
PWR ACC 30a Thermal Breaking that should "trip" w/ Defog "coil" shorted to ground. Plus "On" light in the switch is on the "coil" side & may not turn On w/ that short too.

"coil" wire goes to C200 that's very hard to access. hard to see even looking w/ left speaker out.
then have C302 after that near the left side of rear window. You have to pull the seat & trim to get to it.
Think the purple wire to the "coil" runs in the console OR next to E-brake lever so might find there to see/test. If near the E-brake lever... can be damage from water, feet, etc. as can move out of protective area for several reasons or some fool drilled/screwed something & hit it. But again, your don't tripping the breaker.

But real/root problem is Maybe the alt itself. Or just you installing belt wrong etc. Even working 100%, Defog is 1 of the biggest Amp Draw & your not "tripping" the breaker when On. Old belt, crap pulleys, Installing belt lose or too tight can cause problems & alt etc slips under heavy load then can't make enough power.
see https://web.archive.org/web...ierocave/serpent.htm

Suggest you buy a DC Amp Clamp Meter before bothering anything else.
Example: https://www.amazon.com/UNI-...rement/dp/B00O1Q2HOQ

Many Amp Clamps are AC only for the clamp so watch specs before buying/using other meters.

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(Jurassic Park)

The Ogre's Fiero Cave