This is a '78 300D - there is no relay on the left fender wall- the relay is under the dash to the left of the sterring wheel.

I tried to check the glow plugs today, following the procedure from the online manual and I noticed that as I was checking the voltage from plug to plug and TRYING to check the voltage drop from plug to plug, that after about 10-15 seconds the voltage went from approx. 12 volts to 0. Is the relay shutting down power after so long to the plugs? How long should there be power to the plugs with the key on?

I'm getting a little confused trying to TS this system (again, my first venture into diesels and glow plugs and I've already learned a lot).

thanks, ryan

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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE