rear window defroster relay

I have a 81'SC with a 2 stage window defroster relay in the engine compartment fuse panel - it is the large rectangular one. my question is does anyone know how to test the relay out of the car to see if it is working? I have no defrosting to the window. fuse is ok. any ideas?

Don't you love electrical gremlins?

My first suggestion would be to find someone with a similiar car and functioning rear defroster, and swap relays. If your defroster then works, you know it's the relay. I'm sure their is a way to bench test your relay, but I have never done it.

Have you checked the defroster connection at the rear window and checked for any hairline breaks in the defroster wires? You could also have a broken/loose wire at the rear of the defroster switch.

Hope you find your gremlin.

Regards, Bruce

[This message has been edited by BER (edited 12-26-2000).]

You should be able to hear it click when the defrost switch is pulled. That doesn't prove it's working, but if it doesn't click, then something else is up. As always clean all of your contacts.



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Bill Krause
'79 911SC Euro

Actually there should be two clicks from the relay ... one for each detent position of the Defogger switch!

The most likely problem is corrosion somewhere from the relay socket forward ... i.e., the socket, the 14-pin connector forward, or any connector between the 14-pin connector to the defogger switch, or to the rear window connectors!

If you want to test the relay off the car, you will need four test lead jumpers and a Voltmeter with probe test leads:

1. Connect pin 31 to ground.

2. Connect pin 30 to +12 Volts.

3. Connect pin 86 to +12 Volts.

4. You should hear an audible click inside the relay.

5. Measure the Voltage at pin 87 with respect to Ground ... +12 Volts SHOULD BE PRESENT!

6. Connect pin 86a to +12 Volts.

7. You should hear a second audible click.

8. Measure the Voltage at pin 87a ... +12 Volts SHOULD BE PRESENT!

9. Disconnect the Ground from pin 31.

10. Disconnect +12 Volts from pins 30, 86, and 86a.



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Warren Hall
1973 911S Targa

I had a very hard time searching my rear defroster problem....but one thing I did to check if the hole eletrical sistem was working was testing if there was energy at the wires that connect to the window. If u have power there, everything else is ok. My problem is cracked filaments inside the window.
By the way, if someone knows a way to fix the filaments, else then buying a new rear window...please let me know.

Marcello,

The traces of the defogger can be repaired by using electrically-conductive paint at the point of the crack -- but you must know or be able to find every crack to fix every one. The paint is found at electronics wholesalers and supply stores for technicians.

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Warren Hall
1973 911S Targa