no dash light

[jan lauwers]

Hello Guys,

I have no more instrument lighting. I have read most of the posts here on the subject. I have no popped fuse.

The one thing that I have discovered is that my rheostat was failing, So, I have shortcutted that with the help of the excellent info and pics here. I did the bypassing in the handshake connector. I have tested my bypass by a measurement of resistance and I proved that I have done it correctly. Nevertheless, still no dash light. After some 12 hours of searching, I am really puzzled now, I can’t figure it out! I can manage to read the colored wiring diagram that I have found here on the forum (extremely helpful, thanks to the maker!) … I mean I am not an expert, but I have a basic understanding. (I like to think)..

I believe that I have found one possible cause of my problem: On the male handshake connector, (see pic pl) I have marked with white paint the pin that holds the grey violet wire that feeds the central clock with + current. I don’t understand that, with the headlights on, I don’t measure current on the corresponding female pinhole. On the female part of the handshake connector, the only hole that I measure current on (still with headlights on) is on the opposite pinhole, (where the screwdriver is pointing at on my pic). Is that the cause of my problem? If it is, can anybody help me search further in the right direction, please?

The other bit that I don’t understand is: where does the central clock part get its earth from? I thought that it was the pin on the backside that holds the bracket but that proves to be incorrect I think. (because I don’t measure a connection between the body of the light bulb socket and this pin.

Sorry for the somewhat lengthy explanation… I need help, please!
Thanks, gentlemen.

Jan

[Pawel66]

Not sure if I can help, but sometimes...

Well, sometimes it is the bulb... I know you checked it, but if you connected grey-violet and the three other wires together  and if you have power on grey-viloet wire, lights should be on.
Which light stopped working? Cluster, or all 4 (speedo, tacho, clock and cluster)?

About the side of the pin that is to be powered - if it worked before, it did not change itself. You should have power where you have the grey-violet wire.
Well, sometimes it is... a mirror view on these connectors - plugs and sockets. Double check it. Do not laugh, it happens. I will not tell you how I know it.
Or - you shorted it inside the plug and the grey-violet wire is touching the pin for or the other wire to the other bulbs inside the plug (or vice-versa). If you'd reversed the pins, you would have, I think, just the cluster bulb lit up.

The circuit is:
Grey violet supplies power from fuse 7, it goes through pin, the rheostat and then goes to 4 places (4 bulbs), one inside the cluster, three through pin and wires to speedo, tacho and clock. These three devices have their own grounds. The central cluster gets ground through the pin with the brown wire in the connector.

Look at the wiring diagram we have - it is a quite simple circuit.

[jan lauwers]

Hello Pawel,

Thanks for these thoughts. It's giving me some ideas of other things that I could try. Cant do this for a week now, since I am traveling, but I will let you guys know if I manage to resolve this later on.

Jan

[mbzse]

.../... where does the central clock part get its earth from?

In general, the Mercedes cars have a wire in the wiring harness for earth connection; not just a use of the bodywork of the vehicle.
Here you see the connections for the clock.
Legend:
1.   Guiding pin
2.   Earth (-)
3.   Feed +12V lamp
4.   Feed +12V coil
5.   Seal over casing nut

[jan lauwers]

Hello guys,

I promised that I would report back. My problem is solved. Grey cable coming from the light switch was interrupted. It took me a bit to find the break because it was well hidden in an old connection. Anyway, glad that I have found it and thanks for yr help.

Unfortunately, I managed to break the temp sensor while I was working on the clocks, even though I am well aware how fragile it is and I think I HAVE been careful.

Best regards,

Jan