Having trouble with parents 1991 350sdl. Won't start. Glow plug light on dash doesn't come on when you turn the key on but you can hear the relay pick up. 12 volts on glow plugs. Dash light does come on after about 20 seconds-when it should normally go off? Light comes on occasionally while going down the road. Car has ~100K miles on it and probably has never had any glow plug service. Don't know what the resistance of glow plugs should be or if this is a good test? Can anyone tell me how a gasoline person can test these plugs? Can I pull them out without removing the intake? Is it better to replace them or can they be cleaned and reused?
Thanks
KWB

the reason that the light flashes is to tell you that at least one glow plug isopen circuit.you need to take off the intake to do this job(unless you have very tiny hands and don't mind breaking skin) that said buy awhole set of plugs and put them in.(guess how long it takes for the next one to go bad if you only replace one or two).

I have had a somewhat similar incident occur where GP light stayed on after starting ... then finally went out. Waited about two weeks and it went away ...

Am wondering if checking connections on GPs, on battery ground etc might help ... at least it is very, very cheap.

Let us know what happened.

__________________
George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg

Thanks Guys,
Checked glow plugs and found three open, two around 150 ohms and one at .7 ohmms. No wonder it started in a cloud of white smoke.