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  #1  
Old 03-30-2011, 03:59 PM
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Join Date: Feb 2011
Location: Redding, California
Posts: 240
Nagging electrical problem

Two current questions, among many, and would like your ideas.

It's an '85 190D I've owned since new, driven and cared for by a possessive wife that never let me drive it. She serviced it at dealers throughout her life, and I've learned my lesson. I've spent the last 6 weeks correcting their screw ups and games, most of which I've fixed. I'm in process of 'restoring' and upgrading and among the MANY problems, I have two current electrical problems, a temperature gauge that won't work right and an ignition switch that's screwing up the warning lights.
On the switch, out of the clear through the many removals of the instrument cluster (15 through today,) the seat belt warning light decided to function opposite its normal operation, when the belt is off the light is off, buckle up and the light goes on. The other warning lights are quite delayed in going off, and don't until the engine is revved up. Not sure if it's in the switch or the alternator isn't putting out enough to shut them off. I'm uncertain how it functions. How to repair switch; replace or can it be disassembled, cleaned and repaired?

The big problem is the temp gauge. While I was returning the car home a few weeks back, the temp gauge started acting erratically and finally it quit working altogether after making a buzzing sound a couple of times after start-up. I've replaced the three coolant sensors and no change. I replaced the gauge and the new gauge reacts slightly but barely comes off the turned off position so it's getting some current. There is continuity in the line from the main sensor of the three and the resistance is minimal, about what you'd expect for the length of wire. When the connector on the main sensor is shorted the gauge goes to the top.
There is no corrosion on the various connectors and I've removed and cleaned the ground connections on the grounding block behind the cluster. The fuses have all been replaced and there is no corrosion on the connectors under the electrical center. Everything looked OK.

The big question I have, besides why it won't work, is how those sensors work. I replaced the ones that were in the block (one between #1 and #2, and the other by #3 cylinders,) with the only one listed as the coolant sensor. The one that runs the electric fan I understand. That fan was turning on when the ignition turned on and replacing it solved that. No effect on the gauge naturally. I don't know if the other sensors were previously replaced but they are different and carry different numbers, one a Bura, the other a Bosch that says 120°. I could locate nothing on EPC. The lines to both sensors unite and run to a relay on the left fender and the line then proceeds to the electrical center. No corrosion on that relay either. Are the sensors working in tandem or are the some how fighting each other, and does it require different sensors? I wouldn't think so, but why two? Nothing in the wiring diagrams I've seen.

I'm at a loss and fixin' to replace cluster so if there are ideas, I'd love to have them. I do have pictures.

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Old 03-30-2011, 04:16 PM
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Join Date: Apr 2002
Location: NW WA
Posts: 6,299
I would add a ground to the back of the instrument cluster. On the W123s that will sometimes fix such problems, its cheap and easy
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Old 03-30-2011, 07:01 PM
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Location: Redding, California
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Thanks. I don't think so but I'm going to do it anyway since all my bright ideas haven't worked. I'll try anything and it's not only cheap, it's easy.

I've previously carefully cleaned the grounding connectors by taking an eraser to them. I'd guess they are much the same as the W123's. There was a bit of corrosion on them. I checked continuity all the way from the grounding pin (#1) on the 15 pin main connector and into spots on the printed circuit board from the post connector on the board and everything checked A-OK so I don't think it's a ground issue.

Any thoughts on the warning lights and ignition switch?
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Old 04-02-2011, 01:01 PM
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Join Date: Dec 2009
Location: Bedfordshire UK
Posts: 531
My dash warning lamp problems and how I came across the cure.

Partners w124 300d 0m303 non turbo right hand drive Uk car.

In typical fashion she informs me it would not start and there was no glow plug light.

I go and look at the car and yes no glow light.
Later at work it occurs to me there was only the battery light and the Abs light that were functioning.

After work another look late at night in the dark,so interior light on and then switch ignition on and as soon as the battery and abs light come on the interior light goes dim.

The battery reads 12.30 but the headlights function ok so presuming ignition switch I sort one out to fit next day.

Removed the electrical part of switch and it seems ok,so I hook up my spare to the electrical plug and get the same two warning lights and interior light going dim so nothing has changed.

A while spent checking fuses and the glow plug relay (it is the later version with inbuilt cutout) and it has power etc.

Quite baffled at this stage so unplug alternator and glow relay and turn key to find it all still the same.
Alternator is then plugged back in.

Most times I turn the key I go all the way and let the engine just creak over a small bit ,the battery is near flat so it just turns maybe one revolution.

On letting it turn I sit baffled and then swap back to the original electrics for ignition barrel and find it is all back to normal with the dash lights except for glow plugs which has relay unplugged.

Swap back to the other electrical ignition barrel switch and yes still ok.

Ok so eventually remove the voltage regulator from the alternator to find brushes are very short and worn out.One brush is so worn out that it has soot coating the top of it.

Fitted a new regulator and all ok.
Ok so at the end of the day I came across it by chance,I expected a toasted electrical switch at the ignition barrel.

I do not know if any gauges played up as the other half never mentioned them,I have her trained to monitor the oil and temp gauges so most likely they did not.

The brushes made bad contact in the alternator and the new regulator sorted the problem out,I never had alternator off to check armature though so failure may again rear its head.
We both have the same car with mine being a year younger,mine gets cosseted while hers does not get much attention from me apart from servicing.

The ignition electrical switch is very heavy duty and I can see why they last as long as they do .

One more thing, a tip more than anything,,,I found the 3 screws that hold the electrical part of the switch on quite easy to remove but getting them back in seemed impossible until I secured them to the screw driver with sellotape.

Just mount them on the screw driver and then a small length of sellotape about half an inch wide wrapped around the screw driver shaft with just the bolt head being held by the tape.
Do the bolt up and then just pull the screw driver out and the sellotape comes off the bolt.
Took me around a minute to refit all 3 bolts.

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