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

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

I was under the impression that the glow plug relay was an 80 amp strip fuse instead of a 50 amp.

However, that information applies to cars from the 1980s.

The glow plug light operates almost independently of the relay. It switches off when a temperature sensor reports that the heated area has reached a certain temperature point. The plugs can run indefinitely with no light.

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Thanks Busted,
yeah, the california loop style system used 50 amp fuses. All pencil type plugs used 80 amp fuses.


can an internal short in the relay cause so much heat as to melt the fuse box?

Can a bad glow plug go back and kill the relay?

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

Anyway, I replaced the glow plugs with Beru (Ireland-Fastlane) and also replaced the relay.

All is well again and in fact my fuel mileage has increasd from average 19 MPG City to 21.1 MPG City driving.
Also no more periodic glow plug light flickers.

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