Glow Plug/Relay/maybe some electrial issue???

[Peggysjeep]

Good Morning Forum,
I have a gray market, 1980 W123 300D. The glow plug light does not come on when attempting to start the car, therefore the relay is not doing its job. I have now replaced the relay and the glow plugs.

Backstory: We went on vacation in the W123 from Louisiana to California. Got there no issues, on the return trip in Elko Nevada in the morning after spending the night we went to start the car for the days journey and the wait to start light did not come on, thought hmmm is the light bulb out?, nope it would not start, crank yes but not start. Had her towed to a diesel mechanic in Elko, who was all about diesels and actually owned a car older Mercedes than mine. He diagnosed it as the relay was out and to buy a battery cable to jump the car to get her home. We did not turn the car off that day. Spent the night in Cheyenne Wyoming and jumped it with the cable to start it, all good. We did turn the car off that day but once she was running she started not problem. We get home put her back in the garage and went buy parts. Spoke to my son, SirNik84, and he suggested to change the glow plugs too as he had not changed them when he rebuilt the car. Ordered a new relay, just like the one she had, got the new glow plugs and now back to yesterday.

Change the relay and glow plugs and still no wait to start light and the car is not doing the glow plug cycle. She still cranks so battery is good, it was new with the rebuild. Thoughts of things to check......
I am going to look at the fuses today but I am up for suggestions for thing to look at or test.

Thanks for your help,

Nik's Mom (Peggy)

[leathermang]

Is there a sensor in your car's electrical diagram which reads the ambient temperature of things like the block... the air temperature... ? and then uses that reading to adjust the time the glow plugs are activated ?
If you have one... that seems not to be working....

[Diesel911]

I have been told that the Temp Sender either the one in the Cylinder Head or the one that is built inside of the Glow Plug Relay itself only controls the Glow Plug Light. It is the Driver manipulating the Key that decides if He or She wants to follow what the Light does.
If the Glow Plug Light goes out and you keep the Key in the Pre-glow Positon your Glow Plug Relay stays on till the Timer inside of the Relay turns it off. The Light Glow Plug Light does not turn your Glow Plugs off.

[Diesel911]

If the OP suspects the Glow Plugs are not working He might pull the Electrical Connector that has the Small Wires off and see if when the Key is in the Pre-glow position He is getting Voltage to that Terminal in the Connector.
It lookes like the Red Wire with White Stripe is the one. When in the Pre-glow that would be the Termial that has the Pisitive Voltage going to the Relay.
If there is no Voltage getting to the Relay from that Wire it is likely an Ignition Switch issue or the Ignition Switch itself is not getting Voltage.

I am not sure if the Borwn Ground Wire could easily be checked or not. You could tell if there it is connected but that is about all.


Square Glow Plug Connector, what wires go to it.

#1 Red Wire with White Stripe, Run Start Input

#2 Violet (Purple) Connects to the Starter Solenoid Wire (On Turbo Models at the Terminal Block in front of the Battery) allows Glow Plugs to be on during cranking.

#3 Blue Wire with White Stripe, Goes to the Glow Plug Light. The Voltage comes from the Relay through the Light and to a Ground.

#4 Brown Wire, Goes to ground.

I don't like the idea of simply swapping parts to trouble shoot but the OP is already doing that with the Relays. The OP is dealing with a 34 Year old Ignition Switch and Steering Wheel Lock.

My Car is 4 years newer and I had the Steering Colum Lock innards breake in to spots and while the Ignition Switch was still working when examined one of the several Contact Points was actually burned off one side and it was the Arm that was making Contact.

A few Years a go I about $140 for the Steering Colum Lock assembly (Froma an on line genuine Mercedes Dealer) that included the Steering Colum Lock, the Vacuum Shutoff Valve and a new Ingition switch (made in W Germany). The Steering Colum Lock itself was made in France.
Pelican has them for $117.75; that should also qualify it for free shipping.

[Peggysjeep]

Thanks Diesel911 and leathermang, I will look into both ideas.

[barry12345]

There should be one heavy wire at the relay that provides the heavy current when required for the glow plugs. Make sure there is voltage there. The termination of the wire at that point or at the other end of the wire could be oxidized as well.

That wire is always energized I suspect. Make sure you did not create a short and blow out the strip fuse in the relay as well. This is based on your having the fender relay. Not sure of the year when it was moved from under the dash.

[Peggysjeep]

UPDATE: Did some trouble shooting and the relay I have is bad, even thought it is new. I have a gray market car and it has a Bosch 0 281 003 005 glow plug relay, so I bought another one but it is not sending power from the on position on the ignition to the glow plugs, the relay is not doing its job. We jumped the relay with a battery cable from the positive side to the glow plug post on the out side of the relay (the heavy wire) and the "wait to start" light came on and it went off the car started. So bad relay. I also checked it with the volt/ohm meter and that is how we knew it was not getting power. Sad. Had to get this relay from England. If any one has a lead on a location to purchase one here in the states please let me know.

[funola]

I have a hunch the wire in Diesel911's post "#1 Red Wire with White Stripe, Run Start Input" is not getting voltage with key on. Use a test light or volt meter to check it out.