I have a rear defogger/defroster in my 70SS. The defogger only works in one position of the two position switch.

Could possibly be the switch or the unit. Does anyone know the right voltages and wiring diagram to the defroster, so I can test.

Also, any other hints would be appreciated.

Thanks

It's probably a problem with the switch area. There's a resistor attached to the rear of the switch that runs the defogger in low speed. If yours just works on high, switch problem or an open resistor.

John,

Do you have a source for replacement switches, including the resistor?

Thanks

I don't have a source for replacement switches. Still can find good used ones though. I've seen a few at swap meets. Probably can get one through the TC want ads.
If it's just the resistor these can be purchased separately from an electronics supply house for around $1.50. Just cut the leads on the old one and solder a new one in. If I remember right it looks like about a 5 watt resistor. I don't remember the resistor value. If nobody else knows, and you find that's the problem, I'll go measure mine.

JOhn,

You are right. The switch only works on high. Any specs that you have for the resistor would help. Then I can purchase prior to disassembly and remove and replace in a quick step. Does Radio Shack usually stock them?

Thanks

Couple of things. I would first disconnect the option harness from the fuse block. Remove the connector on the back of the switch and pull the switch out. The car does run without it. The switch could be bad in that position. Check that out. The resistor isn't screwed on. It's mechanicaly clamped in place. It's possible that the crimp joints are the problem. If after measuring the resistor, you still find a bad resistor, don't try and remove the leads. Cut them near the resistor body and solder the new one in. Scrape the old leads before soldering. Looks like about a 5 ohm resistor. 5 watt should do it. Wattage is almost determined by the length.

I just measured the resistance on a NOS switch that I have, it measured 3.6 ohms.