Glow plug light didn't light up. Tried to start and she wouldn't fire. Turned the key a couple of times, the light lit up, went out per normal and she fired up.

All 5 glow plugs are 3 months old. Other than checking connections and the 80 amp fuse, could this be my GP relay on the fritz. How do I check it,,,,,,,I am a complete moron when it comes to electrical stuff and how to use a voltmeter.

PS, it is the original GP relay, 1977 300D.

TIA

JCD

You will need to get a reading on the electical power going into the glow plugs. Easy to do, even for those of us that are electrically challenged. Just hook up a any old volt/ ohm meter with the + lead on the lead going into the glow plug and the - lead to a ground on the battery or engine block. Then turn the key on an see if you get any reading.
If you do get power there, but the glow plugs do not appear to be heating, then it just may be that you got some bad glow plugs. I had some I bought at a local NAPA, they were Autolites, and they all failed in about three months. My research here tells me that Bosch are about the only way to go.
By the way, I found on my 78 300D that I could get a quick indication if the glow plugs were heating by touching them. The plug will get warm quickly.
If you don't get any power at the plugs then with a good fuse you may have a bad relay.

Thanks old Dies. The gp's worked well yesterday, but the light is out again this AM.

I used all Bosch gp's, but I'll use your idiot proof testing method to give it a shot.

Thanks,

JCD

jcd, or whoever else,
Related question to your relay issue.\
My 80 300 TD won't start since a bitter spell of single-digit cold.
I think it is the glow plugs, because i am getting voltage to the plugs.
But what is weird is that after i try turning the engine over, my glow plug light blinks!!! I can't find any documentation indicating what it is trying to tell me.
It goes on when i turn the key, then it cycles off, I turn the engine over. Then I stop turning it over and it blinks at me.

In a mocking sort of way.

Anybody have experience with this. Am replacing plugs tomorrow with new Bosch pencil types.

Any insights appreciated.
wilb

I think blinking or the light staying on after the car is started is an indication of a bad glow plug.

Good luck and put some penetrating oil on each plug and give it some time to work in.

Jim

jcd
many thanks for the response. Just found this site today, and am elated to find so many other people like me nuts about the 123.

will report about my success with installing new gp's.
pulled the old ones today and they were soaking wet. am optimistic that new ones will do the trick.

again, am really appreciative for the response.
will report back.

wilb

My car's glow plug light kept on flashing for 30 seconds after starting. If you let the light go off then wait about ten seconds it would fire up. I replaced the battery today and the light quit flashing.

yes, blinking light must have meant bad glow plugs.
Tip on coating them with penetrating oil very helpful. Went in easy, especially considering access problems.
To put the little tip-nuts on, I used 1/4 inch drive, with universal elbow, and used grease to keep nut in socket. made screwing in the little tip nuts easy. Was impossible to do with my hands.

thanks for all the help.
wilb