PeachParts Mercedes-Benz Forum - View Single Post - Added a jumper wire to glow plug light from glowplug

rhodes2010 · #8 12-06-2010, 07:12 PM

Several here mentioned the glow plugs, and that the light can be an indicator of a bad plug.
I agree.

Earlier in the same day all 5 plugs were removed and tested using a battery charger.

I remove all 5 plugs at the first sign of a glow problem / starting problem.
It is fast and easy to do, and a sure fire way to make sure they glow.

Anyway. reamed the glow plug holes (I do not do this part frequently, only when I feel a bind). Vacuumed out the soot.

Another thing I will do when sensing any trouble is apply a volt meter at each plug and watch voltage during pre-glow and starting to make sure nothing is faulty.

So, 12 volts all checked out, brand new relay that I happened to have in the shop (not junk yard new, factory new). Five working glow plugs.
One 30 year old wiring harness and 323,000 miles.

I am intrigued by Alastairs comment about the bulb at dash end not earthing
and that earthing (grounding for us yanks) at the relay end should light bulb.
This goes contrary to my thinking and experience with exposed metal in
american cars, but I am always open to new ideas.

I have tried an added ground wire to the dash in the past to strengthen the ground signal.
My temp gauge also reads a little funny, but a mercury thermometer in the radiator
and a laser non-contact thermometer each confirm the car runs spot on 80 centigrade.

So those two harness between engine and relay, and relay to cabin carry all this.
The temp and the glow plug light signal.
After all the years I am inclined to replace them .
I have a spare instrument cluster (dashboard gauges), and tried that too.
It changed nothing in the way temp and glow plug light behave.

I really appreciate all the input. Makes me want to get back out there and solve this instead of ignore it.
The car runs great and is a daily driver.