lets start with the glow plugs.

turn on the key, and quickly measure voltage at the first glow plug you can reach.
if you can't reach a plug, measure voltage at the battery, it should be reading around 10.5-11.2 volts. if it's higher, your relay is not energizing the plugs. if it's lower than 10.5, you likely have a weak battery.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!