Blowing 80A Strip Fuse in Diesel Glow Plug Relay
 

1982 300 TD (Turbodiesel Wagon)

Wagon won't start.

Glow Plug Light on instrument panel not lit.

Checked strip fuse in relay, and found it to be burned through.

Pulled the large connector off the five terminals of the glow plug relay.
With negative multimeter lead on battery negative, and positive lead on each of the five female connections on the large connector, I read:

1 2.4 Ohms
2 2.0 Ohms
3 2.5 Ohms
4 2.4 Ohms
5 2.3 Ohms

NOTE: When I touch the leads of my multimeter together to "zero it", it reads 0.3 Ohms. So this value, 0.3 Ohms, would have to be subtracted from the above readings.

As an experiment, I removed the wire from No. 1 Glow Plug and tested the wire only: negative lead on loose end of the wire meant to go to Glow Plug No. 1 and positive lead on female connector No. 1 on large connector at Glow Plug Relay : Results: 1.3 Ohms less 0.3 Ohms = 1.0 Ohms. Is this about what we would expect for the wire only?

Again, as an experiment I pulled the No. 5 Glow Plug and read it out of the engine. Results: 0.8 Ohms less 0.3 Ohms = 0.5 Ohms. So it looks like that glow plug, at least is OK!

Thinking that the Glow Plugs are OK, I reasoned that it must be the Glow Plug Relay. I ordered a new Glow Plug Relay. After installing it, still got no Glow Plug Light on Instrument Panel AND IT BLEW TO 80 A FUSE in the new Glow Plug Relay.

I would be grateful for any ideas anyone may have.

I get less than 1 ohm, wire included. Pull all the other plugs and test individually and if you can, hook 'em up to a 12v source to see if they glow.
Not sure why a new fuse would blow.

Blowing 80 A Strip Fuse in Diesel Glow Plug Relay
 

Thanks for the reply.

When I pulled the No. 5 Glow Plug, I noticed that it was resistant to simply being slid out because it was somewhat "siezed" by the carbon buildup around it, which brings up two questions:

1. Is it possible that the carbon buildup could be producing the "slightly" higher resistance readings (Instead of less than 1 Ohm, I'm getting approximately 2 Ohms, NOT 50 Ohms, or open, or short!

2. Is it a foregone assumption that the precombustion chamber the Glow Plugs fit into needs to be reamed out before installing the new Glow Plugs? Is this reaming a fairly common procedure (meaning: most people do it) when installing new Glow Plugs?

Seems like there must be a dead short somewhere to blow that fuse.

I have a reamer and use it when I install new glow plugs, which I've done to both cars and it won't need it again for some time, I imagine.

There is something in the circuit causing excessive current to flow through the strip fuse. You must locate and resolve that issue.

Physically check for shorts in the wiring from the GP relay to the GPs. To blow a 80Amp fuse the resistance needs to be less than 0.15 Ohms. Almost a dead short.
I've seen the fuse blow on a 300sdl and the fault was a pinched wire under one of the brackets.