2 Stage Rear Window Heater

techguy · 06:59 PM

Hey Guys,

Working on my 2nd last major electrical problem on my 72 Targa!!

Problem: rear window defrost does not operate.

Solutions so far:
(1) Replace fuses, clean terminals, clean all grounds
(2) Check power at defroster switch (lots of power and lighted switch operates).
(3) Listen for clicking noise on stage 1 and stage 2 of relay (no problems here)
(4) Check power on wires going to window (red/white) has 12V in stage 1 and 2.....(read/black) no power in stage 1 or 2.

Now What?????

Thanks!

cary · 10-14-2002, 03:37 AM

On mine, after I pulled the rear glass. I found the male spade was broken off from the defroster grid.
So I may look for another rear window. But my car is just about ready to be put to bed for a long winters nap.

techguy · 10-14-2002, 04:33 AM

Thanks!

I think the wires to the window are ok..I think that is! Do you know if both red/white and red/black wires receive power when the window is on? The wiring diagrams I have only indicate 1 wire to the rear element (red/white) the one I have 12V power on. If I put continuity to both the red/white and red/black lines I get a reading. I also get a reading on red/white to ground and red/black to ground.

marcesq · marcesq's Garage

Did you check for continueity on the rear window itself?? Ohm meter on both spades??

Just a thought.

marcesq · marcesq's Garage

Ok I just looked at the '71 and '73 wiring diagrams, and both indicate that 12v are on one side of the window and ground is on the other. For a test, I would leave the wire on that gets 12v, and do your own ground wire, and see what happens.

The worst thing that can happen is blown fuse.

techguy · 10-14-2002, 09:45 AM

Thanks Guys!

This old girl is a Targa and all her wires connect on the drivers side of the rear window just about were the middle left of the rear deck is. The wires all connect at a junction and of course it is buried by a rubber seal. I have attached a pic...maybe I am missing something??

techguy · 10-14-2002, 03:52 PM

Does anyone know if red/white and red/black to the rear window receive power in stage 1 and stage 2? My red/black wires read 0 in both modes. How do the 100W and 250W stages operate?

marcesq · marcesq's Garage

The 2 stage works through the switch and relay.

Based on the wiring diagrams, only the red/white gets power.

Try connecting the spade with the red/black wire to a ground and see what happens.

techguy · 10-14-2002, 05:55 PM

I think I found the problem! I removed the relay and it sounds a bit like a bubble gum machine on the inside. I carefully removed the protective cover and found the relay on the right hanging from the circuit board. Now what? Does anyone stock these things?