Rear Defrost Not Working

[MicroMachinery]

Soo.. I'm trying to bust a ghost that's causing a significant enough voltage drop to disable my rear defrost on my 73 610 wagon. It's very peculiar, in that all the wires are intact, all connections are clean and good, my defroster relay is functioning perfectly, and the rear defrost switch is switching(with nil resistance, mind you). I have checked voltage going to the rear defroster, and I get battery voltage at the connection going to the rear defroster spade; that is, until I connect it to the actual rear defroster. At that point, voltage drops 3v, rendering the rear defroster worthless. I have checked the ground, and it is 0.1 ohms. When I connect direct voltage from the battery with a jumper wire, the defroster works like a charm, but with the factory circuit, it's leaving me wondering what I'm backing into.

 

I'm tearing my hair out here. I've measured resistance in all wires and connections, all of which yield ideal results. Has anybody out there had an issue like this?

[ggzilla]

It's a bad connection, when the voltage drops under load. Keep tracing it back to where there is no voltage drop and you'll find where the bad connection is. Even though it looks good, clean or replace it.

[datzenmike]

Replace the fuse for it. Check the fuse contacts.

[MikeRL411]

The spade lug from the connector to the printed "wire" on the window is prone to breaking its connection to the grid with fine cracks. It will "pass" ohmmeter checks but not pass full current. Several sources sell conductive copper "paint" used to correct this. You need to remove the insulating layer, clean what is left of the printed copper, apply the conductive copper solution and let it air dry / cure. Then reapply the insulating lacquer from the kit. Should restore full current flow to the printed mesh defroster. I don't have part numbers or manufacturers, just a memory of these kits in old JCWhitney catalogs. Go to there site and search, although their site search function is weird at best.

[MicroMachinery]

Well, if I run a wire directly from the relay to the defroster, it works right now. If it were cracks between the spade and the element, I would have the same result..