Glow plug system

[boxer246]

I'm having a little trouble with my glow plug install for my Vanagon M-TDI.  I bought a early '90s Jetta glow relay, and wired it up. 
For reference, here's the pins:
30-I have this wired through the stock TDI 50a fuse, connected to the large red wire in the black wiring box in the Vanagon eng. compartment.
85-Ground, to body.
50-wired into the starter signal wire
86-wired into a wire that sees 12v only when key in ON position
L- not wired into a LED yet.
87-glow plug output 12V
T- I have no separate glow plug temp sensor on this motor.  Not exactly sure where it should be.  Is the 4 pin type temp sensor that goes into the plastic T coming off the head the correct one to use?  I just have the two pin sensor there, for the temp gauge only.

So here's my problem: During testing, I'm seeing 12V at the glow output wire for too long.  It drops down to about 9 or 10 volts during cranking, but if I let the key return to the ON position, it is still putting out 12V to the glow plugs.  IF I leave the key in the on position, the relay will continue to put out 12V for roughly 40-45 seconds, then it seems to click off.  SHouldn't it only put out for about 7 seconds or so max?  And should it glow during engine cranking/startup? 
Its a German 3.400.200 part number relay. 

So currently I do not have the temp sensor wire connected to anything.  If memory serves, the dedicated glow plug temp sensor simply connects the path to ground, once the engine warms up, correct?  So leaving that wire disconnected should probably just make the relay think the engine is dead cold? 

[vanbcguy]

The glow plug temperature sensor controls how long the glow plugs stay on for.  The warmer the coolant, the shorter the glow cycle.  It's a resistive sensor.  If it is disconnected the relay will keep the glow plugs on for a long time as it will think it is extremely cold.

Everything seems like it is working properly to me for a relay with the temp sensor disconnected; the later 1.6TD glow plug relays keep the plugs on after starting for a bit.  All AAZ and TDI engines keep them on for several minutes after starting; it helps reduce exhaust smoke from a cold engine.

You'll probably also notice that the indicator light goes off while the plugs are still on, should you choose to hook it up.  The indicator light only tells you when you can start the engine, not when the plugs are on.

[boxer246]

Hmmmm......Ok gotcha.  So grounding out that temp sensor wire wouldnt necessarily fool the relay into thinking the engine is hot. 
SO I guess the next question is where on the TDI (AHU BTW) is that temp sensor supposed to go?  Is it that 4 prong sensor like I was saying, as opposed to the two prong, like I have installed now?  I think the one I have in there has a green top. 

[vanbcguy]

I think you should be able to use a 4-prong sensor for an AAZ - it will fit in the single sensor housing on the TDI.  Or I think there was a cooling system flange for the 1.6 that went on the end of the head that had a sensor bung in it as well; that would let you use the late 1.6 sensor that would work with the relay you have.

The 4-prong sensor is just a pair of temperature sensors in a single package.  The TDI one won't work with the older glow plug systems; it seems to send a differently indexed signal from the older sensors.  My AAZ glow plug controller would barely turn the plugs on at all with the TDI sensor.

[boxer246]

Yeah after doing a little more research, like you said It seems like the blue 4-prong sensor is two-in-one....one can be sending a signal to the temp gauge, and the other to the glow plug relay.  I'm going to pick one up from the parts house and see if it works.