The 240D doesn't start. The glow plug indicator on the dash doesn't light. I've checked continuity on all the plugs and they seem fine. When I tried to check voltage, there was no voltage comming to plug 1 (Key on and starter pulled out to preheat position). Checking a wiring diagram, it appears that there is a "glow plug switch and resistance ind" somewhere in the system in front of the glow plug indicator. I've tried tracing wires, but they go into the main wiring loom and I can't find where they come out.
Does anyone know where the "glow plug switch is located"? Thanks!!

My 75 240 d had the same thing going on - I started replacing the fuses, (even tho they didnt look broken) beginning with the 2 fuse blocks on the drivers side under the hood, that had 2 fuses each - the glow plugs heated right up.