Club 80-90 Forums

Anyone got an idiots guide to pins on rear heated screen switch?

Want to use one with a timed relay for my mirrors

Hi chap and seasonal best wishes !

Assuming you're interested in the T3 demister switch, 251 959 621. This has a lamp inside to warn when its on (like the foglamp switch), and also a backlighting lamp so you can locate it when its dark. There are four pins, with terminal numbers next to them, which should be wired as follows:

31 - Earth - brown wire
58b - instrument backlighting - grey/blue wire
75H - X terminal via 20A fuse - black/white 1.5mm (Factory connection is relay plate pin A23, Fuse S14)
75h - heating element - white/green 1.5mm

Some T3 dash harnesses have this connection present next to the other switches, even if no heated rear window was fitted, so all you need to do is plug it in. Otherwise you'll need to add the required connection to the dash harness. You'll need 2 each of 2.8mm and 6.3mm uninsulated crimp terminals, and the correct terminal housing, which is pn. 321 971 837, also used on Mk1 Golf etc.

And a Merry Christmas to you too chap

Done a bit of reading and it would appear that timed relays are on a off/mom switch so maybe timed relay isn't compatible with a T3 switch. Think for authenticity will stick with a T3 demister switch.

Cheers for sharing your knowledge chap

Did my heater fan and resistor today and while dash was out did your headlight relay mod.

Found the wiring for the heated rear screen just as you said, yay!

Just need to get a switch now.

Got some mirror adapters and have fitted some LR mirrors, same size as I had on my 130, bigger than standard defender ones. Think they are 10" and a bit by 6" and a bit.

Got them epoxy primed and painted today and fitted them last thing tonight.

Two monster mirrors and adapters came out at a few quid over £50 big difference compared to syncro ones in price but does same job.

Got a heated mirror kit as well, you can see where this is going..........

Got a switch here if you need one (Wk 20 1989 vintage), both bulbs check OK with a multimeter. PM if interested.