I am trying to solve a puzzle.

If a timer relay for a standard 'loop' (series) glow plug system stays stuck 'on' (energized), will the glow plug light turn off after the normal tima lapse upon key turn?

My new Bosch glow plugs have about 2000 miles on them. Installed by a tech.

Soon after, the system bagan to blow the 50 amp strip fuse about every 600 miles (approx) 2 months+.

Finally now I can measure no voltage at the strip fuse terminals and much less at the plugs. No glow light and no car start. BUT the strip fuse was fine this time.

I figure that the relay (original OEM 1979) died, BUT I want to know why.

Could it have stayed on periodically and toasted the fuse? Could a short in one of the plugs have strained the fuses in the past and finally it damaged the relay?

Can a short anywhere else like the key tumbler cause this? (mine was replaced about 4 yrs ago.)

The latest blown fuse caused some strip fuse box heat damage on the glow plug output terminal end, but not on the other side.

Thanks

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1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
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1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD