Need Help w/Defroster Circuit

[rossiz]

i'm not getting power to my defroster element at the hatch window, but i used to... pulled the 2 plugs at the hatch glass, test light does not light. the 20amp defroster fuse is good.

when i turn the defroster switch on, the blue "defroster" indicator lights up

the defroster relay makes no "click" when i turn the switch on/off.

the defroster relay has a 4-pin plug: 2 pins have constant power (test light lights up between them) when the key is in acc mode, regardless of defroster switch position - i assume this is the power that is supposed to be sent to the defroster elements when the relay is activated by the defroster switch.

the other 2 pins get no power regardless of the switch position

i'm trying to trace the wires from the switch to the relay - they are blue & blue/white coming out of the defroster switch plug, then go into a harness bundle to a large black harness plug on the right side of the tunnel - if i plug/unplug it, the defroster indicator light will light/go out when the defroster switch is turned on

i'm weak in the electrical dept. so need some help to ensure i'm testing correctly...

any help on this would be greatly appreciated!

[Zed Head]

Here's the circuit diagram.  Looks like the blue light just shows that the relay got power, but doesn't show that the relay did its job.  Notice that of the two wire ends over the window, one is just a ground.  Only one has power, you have to pick the correct one.  You can just use your meter and test directly to a body ground.  If there's no power at either wire, but there is power at the fuse, that would indicate that the relay is not closing the circuit, or it's been disconnected.

[Zed Head]

18 minutes ago, rossiz said:

the defroster relay makes no "click" when i turn the switch on/off.

the defroster relay has a 4-pin plug: 2 pins have constant power (test light lights up between them) when the key is in acc mode, regardless of defroster switch position - i assume this is the power that is supposed to be sent to the defroster elements when the relay is activated by the defroster switch.

the other 2 pins get no power regardless of the switch position

Sounds like the relay is stuck or no good.  It's a common normally open 4 pin relay.  Any old auto store or junk yard relay could take its place.  I lean towards the Bosch units from BMW's.  They seem to be of high quality.

[rossiz]

Thanks Zed - good advice as always.

I pulled apart the OEM relay and hooked the test light up to the defroster element terminals and when i manually activated the relay the light came on - problem found.

$4 generic 30 amp 4-pin relay from O'Reilly, cut the OEM plug off the relay and crimped on female spade connectors and all is right in the world.

I managed to hook up my little cheapo heater fan and will let y'all know how it works - I figure I might get one or two more rainy days this season for a test run...