I'm having an odd issue with my glow plug relay, and thought I'd post it here because of Vince's very convenient diagram.
The relay seems to work fine, flashes up the plugs when cold, and turns them off again in a reasonable time. Engine starts smooth, no problems to that point.
The issue arises if I rev the engine past 2500 rpm and the engine is still relatively cold. At that point, the glow plug light will suddenly show that my plugs are back on, and it stays lit for about 3 seconds.
However, once the engine is up to temperature, no matter how high I rev it, the glow plugs do not switch back on.
I initially thought there might be a loose connection at the relay, especially the coolant temperature signal, that temporarily disconnected with vibration (ie. 2500 rpm) and then it re-established contact. So I crimped the hell out of the connections and smeared with dialectic grease. (This is a non-factory install, with female spade connectors attached to the relay, not the factory relay "seat"). However, this has not made any difference. I suppose I should have foreseen that was not the cause, since the T signal *must* be getting through to the relay, since the issue never arises once the engine is up to operating temperature.
Anyone got any ideas what may be happening here?
If I had a small air bubble in the coolant circuit, would the GP relay behave like this? (I have no other noticeable coolant-related issues, so I don't *think* this is the issue, but it's a Vanagon converted gasser, so there's miles of coolant hose, so anything's possible.)
Here's the wiring diagram for the relay socket... it will need to be connected to a dedicated coolant temperature sensor and the starter feed:
The coolant sensor tells it how long to stay on for, and the starter feed tells it to shut off as you attempt to start the car.
Note that it's intended to drive the fuel shutoff solenoid via pin 86... you won't need that line since you have obviously figured out a different way to power the solenoid as part of your swap.