OK, I stand corrected. On my 1981SD the temperature switch located on the thermostat housing near the EGR is the lockout for the heater blower. In EC mode it prevents the blower from starting if coolant temperature is below 33C or in normal mode below 37C. (I guess they don't want to blow cold air in the cabin, or delay the engine reaching operating temperature, who knows) I apologize for any misleading information. The aux fan is operated by a relay, which is in turn operated by the thermal switch on the receiver/drier reaching 52C (126F) Anyone need the schematic?

ok here is the million dollar question
(and yes please the schematic would be nice for records and my possible mod)

COULD one use the temp lockout sensor to also run our violet wire setup? This sensor grounds once it gets hot (I believe from tests) and thus you hook that to the neg side of a relay, the postive to power, and switch the violet wire with the NO contacts (power=contacts closed).

This way, if the engine was cold, the relay would get no juice, the violet wire in turn snipped, and the GP relay on a long time.
When the engine is warm (by previous post statistics) it would turn on the relay (probably have to run it to key on/start = +12v so that it would not be draining the battery when the car was warm and not running)
and thus the relay contacts would close and make the purple wire complete.

Sound good?
I can forge up a schematic if someone is interested...

It sounds like it operates the opposite of the 50C switch on the 603 engine - it grounds when hot, where the 603 switch is grounded when cold. You are correct, just have that trigger a relay and use the NO (normally open) contacts. Should work great!

Only important factor here is that they key power must be on also when the starter is running otherwise the starter signal will never get to the relay (violet wire) when the engine is hot and the GP need not run.

Nice diagram, that is exactly what I'm going to do tomorrow. My only addition will be another line off the relay to an additional light in the instrument warning panel, to indicate when the afterglow is in operation....

At what temp does that sensor trigger? 50C is probably the lowest temp that I'd want as an afterglow cutoff, but a lower temp should help to extend GP life.

On my 81' SD the book says the temperature switch triggers with coolant temperature at 35-40C, or 95-104F. Sounds reasonable to me. While not full operating temperature, that's hardly a cold-soaked engine. I'll let you know how mine works out..

Ok, after some work, I got the setup all done with a relay through the temperature switch and..................... Ugghh.. It turns out that the ground to the temperature switch is dependant upon the settings on the acc panel ... unless you are asking for full heat, the line is grounded all the time anyway. So in the end I just mounted a matching switch next to the headlight switch.. Works nice and gives full control..

Couldn't one incorperate a diode into the circuit so that the ground only flows from (electrons from negative to positive) the sensor to ACC panel and then put the relay setup on the sensor side of the diode?

I am just bound and determined to not have too many buttons, lights, and switches on this car (even though they are fun)

Hey Brandon. Yes, I think the diode would work fine and to be honest, wish I would have thought of that yesterday. My switch matches nicely and is hardly noticeable. When I did the relay I installed everything in the current fuse box, put it all back together and it looks completely factory.. Maybe I'll upgrade to the automatic next time I'm doing a project under the hood.

Sounds good to me. I'd put a switch in there but I like having it so that my car can take care of itself independent of the driver in the occasion that someone else drives it :-D
I planned on putting everything in the fuse box and was really hoping to find one of the stock silver relays and sockets to put in there. Anyone have an extra relay socket/relay for a w126? heh
All else fails I'll drop a bosch in there and call it dandy. Did you include anything in the dash for the glow active light?
I was thinking about this but it seems like getting ANYTHING through the firewall is a *****.

Thanks!

Atleast you KNOW what a diode is...sheesh...trying to explain these electrical thing to my dad's friends, my fellow VW owners, etc. is really difficult at times. Back to basics

I ran some lines through the firewall before and yes, it's a b!@tch. Since I ended up with a switch, I didn't install a light, but it is extremely easily done, Lots of blank spaces in the warning panel... I bought a continuous duty relay to use, which is what I recommend because the mercedes relays get plenty hot under continuous loads...

does anyone have a working schematic of the glow relay circuit.it may also be possible with a resistor and capacitor to add a time delay function to the internal relay of the glow unit

Ah alright...have noticed the merc. ones tend to get a little warm heh
I'll just pop a bosch one..
what kind of holder apparatus did you use?