I am troubleshooting my 300D 2.5 which has a glow plug fault. I have ohm'd each of the glow plugs at the glow plug connector to the glow plug relay. Each of the 5 are within .7 ohm range. I have even purchased and installed a brand new Beru (not MB) glow plug relay. The OEM has an internal fuse while the Beru has an external fuse. I don't know if it really matters.
There are two 5 pin connectors on the glow plug relay. The larger one has 5 pins, one for each of the glow plugs in the engine. The other 5 pin connector is much smaller and one would guess it must be responsible for activating the relay and illuminating the dash glow light.
When I turn the key switch to glow, the dash glow light will sometimes light, but most of the time will not. If I turn the key back and forth multiple times, it will sometimes cause the dash glow light to illuminate as expected. But again, most of the time the dash glow light will not illuminate. When I measure the voltage at the relay, I am getting slightly more than 12v at pin 1 of the 5 connector on the glow plug relay. Yes, the 300D 2.5 turbo has a 5 pin connector at the relay instead of the 4 pin on earlier diesel models ( I have an '87 300D Turbo with a 4 pin connector).
Could the fault be at the key switch?
Does anyone know what each of the 5 pins on the connector to the glow plug relay is intended to do? What voltages they are to have at glow and cranking? And which of the 5 pins is responsible for lighting the dash glow light?
I am seeing threads with questions about the a faulty glow plug system. I have read them and tried the solution(s). So far no luck. I certainly would like to improve my diagnostic skills, but I am stumped.
If anyone could help, it would be greatly appreciated!