Glow Plug Switch 1975 w115 300D part 0015451832

[Orango]

I’m have a problem with my glow plug switch staying activated without turning the ignition switch (key).

I have a battery drain and have to disconnect the battery when I leave the car overnight. When I reconnect the battery the glow plug light is already lit and goes off when it’s heated up (5 seconds or so).

I found the glow plug switch under the steering column and disconnected it. There are two little switches (toggles) (pointed out below) that I’m going to spray with WD40 to see if it helps.

Any ideas would be appreciated. Thanks in advance.

[cleeves]

In the pictures, both of your relays are in the off position.

I'm having a bit of trouble understanding the symptoms as you have described. But I doubt it is in need of WD 40. If they go out when the glow plugs are warm, that means the relays are functioning. It seems that the signal from the ignition switch is in error.

So, if I'm not mistaken, the key has no affect on the relay? So when you plug in the battery it just clicks the relay on?


Henry

[Orango]

I have a new starter, alternator, and I replaced the switch in the ignition assembly.

The car runs great but it’s unreliable with the battery drain. I was hoping I found it with the glow plug relay but looks like it’s functioning fine (thanks).

I’ll keep at it and see if I can track down the problem.

Thanks again.

[801mbz]

glow plugs can stay on after dash light goes out test #5 for power with a test light if it stays on after starting relay is bad replace it or re rig it some some how plug and un plug relay as needed or ????

[Diesel911]

I don't know about these older cars but I am looking at the schematic and I am seeing inside of the Glow Plug relay 3 diodes and what I believe is a Transistor (not entirely sure of the symbol for that). I am guessing one of this in the relay is what is causing the issue.

The voltage that activates the relay appears to be #5 on the Electrical connector and #30 on the relay or at connector #3 and relay #50 and comes from what is called in the diagram the Steering Lock Starting Switch.

One circuit is going to be for when you apply the Pre-glow before you start cranking and the other connects and has the glow plug relay on during cranking. I don't know which is which.

See if this will function for you:Mercedes-Benz Model 114/115

[Idle]

While you have it open you might drag a points file through the ignition points looking things. I always do because it is just a matter of time before they start to arc and burn out.

That matter of time might be sixty years, but cleaning the points (you might see this addressed in the service manuals as 'dressing' the points) is never a bad thing to do if you have them exposed.