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  #1  
Old 01-08-2012, 05:40 PM
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w123 300d - no climate control lights

A few weeks ago, the climate control lights and shift indicator went out on our w123 85 300D. Today, I finally got to it.

Previously, I had jumpered the rheostat - no problem with instrument cluster lights.

But, now I am stumped. I have no power to the christmastree-like light string at the panel and the spider at the firewall. But, I do have power to the shift light bulb, which according to fusebox diagram is on the same fuse.

I checked fuses, even switched them around, but it seems climate control is shared with shift indicator and several other things. Everything else seems to be working. A blue wire feeds the Climate control/spider circuit, but it disappears through down near the firewall, presumably going to fuses or thereabouts.

I don't have a wiring diagram. Can anyone tell me where that blue wire goes?

Some of the bulbs were bad, but surely they are not in series? No, no power on circuit anyway.

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Old 01-08-2012, 05:42 PM
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I believe the Haynes manual has a diagram in there, if you've got one? Other than that, I can't be much help to you.
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  #3  
Old 01-08-2012, 06:33 PM
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Same fuse (1), but different locations in the circuits. Per the diagram (check PM) the shift bulb is not dimmed and it comes off of the headlight switch. The console lights come off of the rheostat.

The diagram shows a blue wire going from the PBU to junction C124 behind the console. C124 should have a few gray/blue and blue wires on it. It gets power from the rheostat, so if you jumpered the rheostat you MAY have disabled power to this junction by that mod. Power comes out of the instrument cluster pin 12, a gray/blue wire.

Another possibility is if you messed with the radio. The radio also gets power off the rheostat for the light bulb, so changes there may affect the lights.

Did you also lose the light bulb in your hazard switch? That's also downstream of the rheostat. If not, then the problem may be downstream of C124; if so, then maybe between c124 and the rheostat.
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Old 01-08-2012, 07:23 PM
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Originally Posted by Yak View Post
Same fuse (1), but different locations in the circuits. Per the diagram (check PM) the shift bulb is not dimmed and it comes off of the headlight switch. The console lights come off of the rheostat.

The diagram shows a blue wire going from the PBU to junction C124 behind the console. C124 should have a few gray/blue and blue wires on it. It gets power from the rheostat, so if you jumpered the rheostat you MAY have disabled power to this junction by that mod. Power comes out of the instrument cluster pin 12, a gray/blue wire.

Another possibility is if you messed with the radio. The radio also gets power off the rheostat for the light bulb, so changes there may affect the lights.

Did you also lose the light bulb in your hazard switch? That's also downstream of the rheostat. If not, then the problem may be downstream of C124; if so, then maybe between c124 and the rheostat.
Thanks for above and PM! I understand and will troubleshoot tomorrow. I haven't done anything to car since Spring, so wire might have just rattled loose or maybe I have a bad ground. Whatever, I guess the cluster comes out again!
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  #5  
Old 01-09-2012, 05:45 PM
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OK, I pulled the cluster and took it apart. Looks like I have a broken trace and another one almost gone. Why would that happen? Fuse should blow first? Bulbs are 1.2watt but there are quite a number on that circuit. Should those bulbs have a lower wattage?

Looks like I can probably solder on a jumper to replace those traces. Or maybe I could find a used cluster?



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  #6  
Old 01-09-2012, 06:04 PM
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Find used cluster. You could wind up soldering then soldering the next tracer . . . like Tom Hanks following the wiring in "Money Pit." LOL. Just check the cluster back to make sure you're not getting the same thing.
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  #7  
Old 01-09-2012, 07:46 PM
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Find used cluster. You could wind up soldering then soldering the next tracer . . . like Tom Hanks following the wiring in "Money Pit." LOL. Just check the cluster back to make sure you're not getting the same thing.
A used cluster would be best.

But it looks like the bad traces are from pins 12, 11 and 15. 11 & 12 lead to and from the rheostat. 15 seems to be a ground (going by brown color on wiring diagram. I may be able to hard wire those. But it would be nice if there was a diagram somewhere of the circuit board.

My concern is first - why did those traces burn out?

ADDED: I took the LH Cluster board apart - this gives better access to the circuit board. Here is another picture. Looks like I may just bbe able to solder a dew small wires and get this fixed!
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Last edited by Graham; 01-09-2012 at 08:23 PM.
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  #8  
Old 01-10-2012, 01:27 PM
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In checking if there is a short somewhere, I should really locate C124 - Anyone know where it is?

The cluster is repaired, but I would like to be sure there are no shorts before I power it up again.

I have checked from pin 12, but that feeds various things - It shows 215 ohms with all centre console bulbs removed, but not hazard or window switch lights. (or radio)
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  #9  
Old 01-10-2012, 07:49 PM
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Couldn't find C124, but after unplugging centre console seat/hazard switches, I measured infinite resistance from pin 12 to ground. I checked the climate control and dash lights and all now work.

I have the switches on my desk. But I don't really know how to test them. It looks like 6 is the feed from the dimmer circuit and 4 is ground. Lighting appears to be through LEDs. I tried measuring resistance between terminals 4 and 6. Starts off at 0.00 which is disconcerting, but then increases quickly - 0.1 - -.3 0.5 MOhms and so on. Same for all switches.

Any idea if this is normal?

Diagrams here
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Old 01-10-2012, 08:51 PM
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It may depend on your meter and how you're testing. Two quick hits from google:

Meter check of a diode : DIODES AND RECTIFIERS

Testing Diodes

I assume that the switches don't work when plugged in and you're now trying to isolate if it's the wiring or the bulb.

I'd put the meter in DC V and check across sockets 4 and 6 in the car. That doesn't help you at your desk though. Got a battery at your desk?

This DIY is also my catch-all for benefitting from someone else disassembling their dash: PeachPartsWiki: Replacing the A/C Evaporator

I'd guess the C124 connector is somewhere near the driver's right foot, based on the presence of numerous blue wires in that vicinity.
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Old 01-10-2012, 10:42 PM
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Originally Posted by Yak View Post
It may depend on your meter and how you're testing. Two quick hits from google:

Meter check of a diode : DIODES AND RECTIFIERS

Testing Diodes

I assume that the switches don't work when plugged in and you're now trying to isolate if it's the wiring or the bulb.

I'd put the meter in DC V and check across sockets 4 and 6 in the car. That doesn't help you at your desk though. Got a battery at your desk?

This DIY is also my catch-all for benefitting from someone else disassembling their dash: PeachPartsWiki: Replacing the A/C Evaporator

I'd guess the C124 connector is somewhere near the driver's right foot, based on the presence of numerous blue wires in that vicinity.
Thanks for input. I will read through that stuff.

I don't have a problem with the switches themselves - Just trying to make sure there is no obvious short before I put them back.

The way I modified the cluster board means that the other night lights are now hard wired. No more dimmer or circuit board traces used except for the two cluster bulbs.

Doesn't make much sense to me that the cluster circuit board has no protection other than the 8amp fuse. Those traces would blow first if the night lighting wiring was accidentally grounded.

Switches will go back in tomorrow and hopefully that will be it for now!
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Old 01-14-2012, 04:47 PM
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I posted much of this in the DIY section on cluster repair, but thought I might get more help here:

It seems to me that those traces for the cluster/console lighting circuit create a weak point in the cluster circuit. Any overload and they will blow before the 8amp #1 fuse. I thought about fixing the traces and adding a fuse, but in the end decided to eliminate the dimmer circuit altogether and bypass the burned traces by running a wire to feed the two dash bulbs. I shorted pins 11 and 12 which really takes the cct board out of things so far as the center console lights are concerned. (small red circle in pic)



I should probably have run the red wire directly to the dash light connection on the board, but instead went to one of the dimmer connections, so I still have one lighting trace in use, but only for the dash bulbs. If I ever install LEDs, I will change that.

I decided to replace the burned ground trace to pin 15 by running a ground wire from pin 15 to the connector that the main ground screw connects to. (white wire in pic)

All the dash and console lights now work as they should. But now, I do have a problem! The temperature gauge goes full scale as soon as the ignition key is turned on! Would that indicate a short to ground on pin 2? I did not go near pin 2 (1 is next to 15), so perhaps the short is somewhere else?

The temperature gauge seems from the cct diagram to have 3 connections. It is not clear to me what the connections between the fuel gauge and the temp gauge do? Lighting?

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Old 01-14-2012, 10:28 PM
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I'm speculating here, but are you sure the wire from 15 to the tab should be there? You may have grounded the case, which provides a path to ground for the temp gauge. What did the fuel gauge do?

If the trace goes from 15 to the tab, then I guess it's correct; but I don't recall that being a "ground screw" but more of a "continuity screw." Maybe it's the same thing?

I also know that the traces in the corner near the case screw and where your white wire is can "wear" due to friction with the case. Is it possible the white wire is being pinched and is distorting or cracking the traces there?
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Old 01-14-2012, 11:15 PM
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I am going to pull it and have a look once it warms up a bit here (zero F here tonight!). The wire was just installed so I can't see there being any wear. But something must be wrong!

The ground wire that has to be disconnected when the cluster is removed goes to that screw tab, so I figured it should be a good spot!

I was a bit puzzled as to why they needed a separate ground going through pin 15. But maybe that is the main ground and the one I used is just an additional one. Once I have it out, I will follow the traces and perhaps run the white wire to where it should have gone!

The temp gauge only seems to be grounded out in the engine bay. When key is turned on, it goes from zero to full scale.

Bill Hunter wrote in the DIY General forum:
"Field expedient upgrade:
On the rear of the fuel gauge circuit board there is a square tab (screw mounts through it) grounding the speedometer assembly.
Make/install a ground wire with two spade connectors in the center, mount it from the square ground point to a solid body ground.
This reduces/eliminates most instrument cluster electrical issues.
The spade connectors in the center of the home made ground wire are for easy instrument cluster removal in the future."

Seems to imply that that tab is a good ground point.
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Old 01-15-2012, 11:38 AM
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Quote:
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OK, I pulled the cluster and took it apart. Looks like I have a broken trace and another one almost gone. Why would that happen?
In my case, I have a short on the left rear door harness. What i did was to put a 1 amp fuse on the blue wire between the instrument cluster and the center console. Everytime i used the left rear door, it would blow the fuse. I unplugged the left rear switch for now until i can fix the harness. Same thing happened to me with the broken traces but i only soldered them together using thin telephone wires-not jumping from pin to pin.

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