w114 rear window defrost relay location?

[Ten13]

Hey there,

I'm wondering if anyone can guide me to the location of the rear window defroster relay in my '74 280 Sedan (w114).

Thanks in advance!

[gmog220d]

Here's what I could find in my Spare Parts List for W115, printed July 1973:



It looks like the "electrically heated rear window" system has its own wiring harness, isolated from the car's other wiring. That could make it easier to follow the wiring from the switch to the relay. The relay is item #59 in the diagram, and is called "Time-lag Relay". The diagram makes it look like it's under the dash, and it also gives an idea of what it looks like. Plus, I don't see a relay that looks like that under the hood of my '74 240D.

Hope this helps!

[gmog220d]

The relay you're looking for is SK 6420. I looked in my stash and found a box of stuff from under the dash, and found a relay which looks like the one in the diagram:



I searched for "relay sk 6420" and found multiple hits confirming it is the Time-Lag Relay for the heated rear windshield. At least now you've got something to look for, and I'm pretty sure it's under the dash on the LH side.

[Ten13]

Originally Posted by gmog220d

The relay you're looking for is SK 6420. I looked in my stash and found a box of stuff from under the dash, and found a relay which looks like the one in the diagram:



I searched for "relay sk 6420" and found multiple hits confirming it is the Time-Lag Relay for the heated rear windshield. At least now you've got something to look for, and I'm pretty sure it's under the dash on the LH side.

Thanks so much for this - I now having something solid to go by to troubleshoot. I have a *very* original, low-mile car that, as best I can tell, hasn't ever been taken a part inside. I'm trying to minimize doing anything that might break plastic tabs or trim parts. Will look in to it!

[gmog220d]

Originally Posted by Ten13

I'm trying to minimize doing anything that might break plastic tabs or trim parts. Will look in to it!

No sweat! Glad I could help a little. I'm pretty sure all you're looking at to get to the relay is removing the panel from under the dash on the LH side.

I assume you are trying to get the rear windshield heating system working again. When you get it figured out let us know what the trouble was. I've had two of these cars and neither had functioning rear glass heaters.

[Ten13]

Correct - the rear defogger doesn't work, and there's no audible relay function. There is power to the switch, however. I'm not going to any great length to repair it... but this is all super helpful. Thanks again! Will keep you apprised of the project's success (if there is any).

-greg

[Ten13]

Update to my findings...

Power is getting to the switch, and to the relay. It is located to the left of the steering column, and is easy to access. I'm assuming that the reason the system isn't working is due to some issue with the filament or its connections at the rear window.

As such, I decided to not pursue the repair. This car doesn't get driven in foul weather, anyhow...