Defroster Lines (Glass) testing

[7783911]

I have been trouble shooting my defogger circuit these past weeks and have narrowed down to the glass elements

It may be that the wire connections are the problem. I tested output to the circuit from the relay harness and get 13V

I then attempted to test line continuity but realized my tests were incorrect since I didnt physically detach the brown ground circuit wires from the grounding post...the results shows continuity on circuit 2 (high) but none on the low.

I had read two posts that explained how to test the actual wire elements

1: Multi-Meter set to V, ground the MM and run the red probe across the lines to see if there is voltage and if there is a break (voltage drops to 0)

I tried that and all lines exhibited voltage (albeit on 4.5 V)...so if thats the case then are my circuits intact (i am trying to avoid the final phase of the repair which involves removing the glass and testing wiring and the glass connection itself)


2: Same as above but setting to continuity on the MM. That was a failure as OL was the only reading despite some voltage on lines from test 1 and the test at the harness side


Can anyone suggest how best to test these lines before I dig into accessing the brown and red connections in the seal (ouch)

Thanks

Bob

[EC900]

Your rear defogger thread is interesting as I have a similar problem.
It also reminds me long ago that on my VW the grid lines were cracked or scratched and broken on the interior side, these are basically silkscreened on. There used to be a product that can bridge broken connection lines.

Visually, my (CA sun-baked) 911 defogger grid is quite discolored in places and maybe even deteriorated to the point it no longer useful although current still sent to the rear terminal connectors and dash knob still lights up.

Found this video helpful but I think 911 grid is a loop circuit as opposed to a domestic, end-to-end connection, two terminals on driver side .

https://youtu.be/tny-8wGGcw4

[7783911]

That video is interesting, must be nice to have access to the actual window circuits :-)

So in our case to mimic the second test, I guess I could connect one lead to the actual relay output wire that goes to the window circuit by creating a bridge wire between relay and the 2 power wires and have a jump off on it to attach the multi-meter. then run the other MM probe across the window lines? Make sense?
Ours is a 2 circuit defog but one could test each circuit independently unless there is some kind of co-reliance between the 2 cicuites (I dont see any in the electrical schematics..just 2 circuits)

[EC900]

Not sure if you found these early posts I bookmarked for reference, maybe the info here can clarify better;

wiring the rear window defroster 1974 targa

Question on rear window heating elemnt wiring

[7783911]

Yup

got those and stole some content for the defroster primer I posted

I m going to take the rear shelf out and see if I can locate the wires/tabs to further my tests