• The Forums are now open to new registrations, adverts are also being de-tuned.

Glow Plug Relay Problem

dot

Member
Joined
Feb 8, 2013
Messages
42
Location
Norwich/London
Car
1985 W123 300TD & 1990 W124 300TE
Evening All,

I’m working on my 92 300 TD and am a bit stuck.

All running fine and no history of electrical issues. Done my insurance so my son can drive it, but have had to have a black box fitted.

Fitter arrived and had trouble finding a spot so was talking to his mates on the phone for advice, but finally fitted it in the driver’s compartment, under the carpet near the transmission tunnel just in front of the seat, the forum won’t allow me to upload a picture.

Anyway, two days after the glow plug light flickered a couple of times before cold starting, and then stopped coming on at all when the key was turned on.

So I ran some checks centring around the glow plug relay. It had power in. I unplugged the six pin outlet plug and tested the resistance and continuity and found no issues. Readings range from 0.8 to 1.4 when set to 200 ohms. I’m assuming that’s acceptable. But when I checked each of the output from the relay when I turned on the ignition it gave me about 12.3v for around 30 seconds then reduced to 7.7v and then off which flummoxed me a bit. I had another relay, so I installed it and the glow plug light came on, engine started and so problem solved. But the following day the same thing happened.

So I’m a bit stuck. Is it too much of a coincidence that a bloke has placed this black box into the electrical system, or am I barking up the wrong tree. I’m really stuck and being quoted £100 for an auto electrical just to come and look is something I’m trying to avoid.

Thanks, Dot
 
Last edited:
Have you checked the resistance of each glow plug? I have heard they can cause problems with the relay when they fail, I may be completely wrong however. Can you disconnect the black box to see if it makes a difference? Did he drill any holes or disturb any existing wiring, might be worth trying to trace back all of his work along the wiring.
 
Matthew thanks for the reply, I’ve been working until today and haven’t been able to look at the car.

Ok so yes I checked the resistance on each glow plug and it checked out ok.

I checked the relay again, it’s getting power, and is giving out power, then stepping down the voltage after about 30 secs.

I checked continuity and I seem to have it from the 6 pin plug to each glow plug.

I then turned the ignition on and tested if each glow plug was heating. 1-5 all said 150 degrees, and 6 said 50 degrees. Bingo I thought, so I removed the inlet manifold and removed all the glow plugs to look a bit more closely.

When I powered them up with jump leads, they all lit up, and said around 500 degrees. Damn I thought.

Anyway I checked all the new Beru ones I’ve got and they heated to the same temperature. Plus their resistance is all 0.6 ohms.

All of a sudden I’m thinking my problem is not the glow plugs. So I fitted the new ones, torqued them up and reconnected. I thought now would be a good time to reconnect the battery and see if my problem was solved.

It wasn’t, no glow plug light.

So now I’m at the end of my knowledge. Do I have a broken wire somewhere? If so how do I check it?

Does the fitting of the Black Box under the carpet in front of the driver’s seat play into this? Where this is I can see the vacuum system pipes but what wires are travelling here, and are they permanent live?

Are there any other factors I’ve not thought of?

Would appreciate and tips or assistance.

Thanks

dot


Sent from my iPhone using Tapatalk
 

Users who are viewing this thread

Back
Top Bottom