I just changed the #1 glo plug trying to get the dash light to come on. Everything went fine till we tried to start the engine. The fuse on the relay blew. Any ideas it's an 87 300sdl.

Some when a direct to ground somewhere in the circuit might have happened. COULD be within the relay itself. If it only happens on the #1 plug, you have a starting place for the VOM.

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1987 300D (230,000 mi on a #14 head-watching the temp gauge and keeping the ghost in the machine)
Raleigh NC - Home of deep fried sushi!

jeffery,

Same happened to me. When I tightened a GP nut, the terminal turned and touched a metal part: Direct short circuit.

Check GP wires and terminals and eliminate any shorts.

P E H