w124 Instrument Panel Woes

[bobman006]

Hi all!! Long time lerker, first time poster The information on this board has been invaluable in helping me with my car. Thanks all!!!!

So, I removed my instument cluster on my 87 300d today to fix my seat belt warning relay. Turns out it was just unplugged and plugged the harness back in and it works fine now. In the midst of doing this, I unplugged the glow plug light and the tach power line to get my hand back to the relay without yanking the whole panel out


Anyways, the tach power line and the glow plug light line touched each other. 2 seconds of sparks and smoke later, and my tach and glow plug light dont work. The clock on the tach still works but loses about 15 mins every hour, so it kinda doesn't work . I checked all the fuses in the fuse box and the one on my OVP and they are fine. I'm figuring that I blew the light for the glow plug indictator but Im not sure and have no clue about the tach and the clock. It could be my OVP as I have rough idle, no a/c and now no tach. My OVP rattles internally when I take it out, so I have a new one ordered but its not coming until monday so I can't rule that out yet.

Am I missing fuses that I need check? What should I look for next?

[babymog]

Why can't any of these be near me so we can swap parts?

If you're talking about the single power wire plugged in behind the tach, I believe that it is clock power.

The GP light? Is that an LED? If so, it's likely fried with direct 12v. If it's a 12v bulb, you can't burn it up with a short, it is a short there is no power in a diesel benz that will burn out a 12v bulb.

Odd problems. I'd start by unplugging and removing the cluster and reinstalling, or get enough access to check and plug in all of the wires.

[bobman006]

Originally Posted by babymog

Why can't any of these be near me so we can swap parts?

If you're talking about the single power wire plugged in behind the tach, I believe that it is clock power.

The GP light? Is that an LED? If so, it's likely fried with direct 12v. If it's a 12v bulb, you can't burn it up with a short, it is a short there is no power in a diesel benz that will burn out a 12v bulb.

Odd problems. I'd start by unplugging and removing the cluster and reinstalling, or get enough access to check and plug in all of the wires.

I hope you aren't insinuating that my car is a parts car.... lol

Is there a separtate power line for the tach?

What kind of LED do I need to replace the indicator light?

Now that I'm privy to the warning buzzer, I was wondering if the current for the instrument panel is always on or just when you leave your key in the ignition. I apologize if I'm too much of a nOOb, but I don't want to zap anything else in my further electrical endeavors

[babymog]

There is always power to the clock, the separate wire mentioned behind the clock/tach.

The light switch turns on the lights.

Other than those two, I believe that there is no power to the IP with the key off. Typically it is best to disconnect the battery first, as you have found, just to avoid damaging expensive parts.

I don't know about the light. I will be pulling the IP from my parts car in the next few days, might be able to tell you then if someone else hasn't. Also, the FSM/Factory Service Manual (respecting your noob status) might be a good resource here to determine how the GP light is powered.

[bobman006]

I'm planning on pulling the instrument panel. While I have it out, I'm going to try to replace the glow plug indicator light if I can find the right one. The dealership would know but I don't like going there

Unfortunately, I don't have a factory service manual. If I can get more information on how the tach works and how the glow plug light works, I would be very grateful.

[Jeremy5848]

I just had my '87 cluster all apart to fix a bunch of problems. AFAIK, the only LEDs in the '87 are in some of the switches (power windows, etc.).

All of the various indicators in the cluster are small incandescent lamps. The dealer will have them, the aftermarket people might have them. Be careful, some lamps look OK but are just a couple of mils too large to fit in the sockets.

Disconnecting the battery and marking the various wires to the cluster is a must, else problems like your arise. As has previously been said, the only power to the cluster with key out is (a) 12 Volts to the clock and (b) IF the lights are on, power to the cluster illumination rheostat and lamps.

The "tach power line" that touched and made sparks is the clock power wire. It has 12 Volts on it all the time. It should not have made the glow plug lamp burn out, as a previous poster noted. Much of the internal wiring in the cluster uses printed traces that might have fried when the short occurred. You probably should disassemble the cluster and check for damage.

When you take the cluster out, you will see that one of the indicator lights in the lower row is attached to the back of the cluster by a wire pigtail so it stays with the cluster. All of the other lights are in sockets in the cluster or are on wires that stay with the car. When you go shopping for lamps, take the cluster along and make sure the new lamps physically fit into the one socket. The other lamps in that row are the same kind -- 12 Volts, 1.2 Watts.

BTW, the lamps in plastic sockets that twist and come out of the cluster are all one piece, lamp and socket. The lamp is soldered and glued into the socket piece. The entire thing is replaceable.

The clock has two electrolytic capacitors that fail with age. My clock didn't work at all until I replaced them, now it runs just fine. Replacing the caps is something you can do if you have the tools and ability to solder on tiny PC boards. If not, have someone do it for you or buy a replacement clock.

Jeremy

[tobybul]

I sorta have a similar issue with the seatbelt and gp lights on my W123. I finally have the bulbs that i ordered but have not gotten a chance to remove the cluster and put them in yet. I think I burned the bulbs.

[jfikentscher]

Is it possible to replace the outside temp display on a 1987? I think I can get one from the salvage yard.

[Jadavis]

Note to self...unhook battery when removing dash...got it! Something good did come from this. I learned from your mistake.

-Jim

[babymog]

Hijack:
Yes, the outside temp display is replaceable. If you get one from the salvage yard, depending on the month your car was built, you might have the 4 or 5-pin temp display unit.

The 5pin is the late-'87 (9/87 on) display.

You can use the 5pin, all new replacements are the 5pin.

Buy the display from the salvage yard, get a 5pin unless you are SURE you have the 4pin. When you buy the display, get the plug/pigtail also, you will need it to reconfigure your wires to fit. The 5th wire (pin 4) is a speed-sense wire, if configuring a 4-pin car to fit a 5-pin display, you don't use it, it will be fine.

[tobybul]

Originally Posted by Jadavis

Note to self...unhook battery when removing dash...got it! Something good did come from this. I learned from your mistake.

-Jim

Exactomundo on this one.... this will avoid any sparks...

[bobman006]

Thank you so much for the responses.

I pulled the instrument panel today and disassembled the tach. I could not find any burned traces on the board. So I put it back in and the tach and glow plug indicator light still do not work. I discovered that the clock only works when the car is off .

I came across another thread who had the same problem but in a w201 car and lost his cruise control. My cruise control hasn't worked in a while and I have no intentions on fixing it but it made me wonder if the problem lies somewhere other that the instruments themselves.

I have no problem replacing the tach and clock (I will replace my temp sensor LCD while I'm at it) My consern is that putting a new tach and clock in will not fix my problem

If anyone has any comments, I would greatly appreciate them.

BTW, disconnecting and reconnecting my speedometer cable made my needle stop jumping at low speeds

[aersloat]

Just FYI on the temp LCD. Mine appeared to not be working but after pulling the cluster it would sort of work - flicker on and off for a few minutes -- and then go completely blank again. It was the actual sensor that was bad. It is easy to check if your sensor is bad. You can check the ohms between the two leads. In my case it was shorted. I replaced the sensor cable from the fender to the circuit box and the temp display works great now. The cable is a whole lot cheaper than an LCD, and if you have a bad sensor a new LCD isn't going to help you.

[jfikentscher]

The Temp LCD looks like a cell phone disaplay that has been dropped and is all discolored. I'm assuming that is a bad sign for the LCD.

[Carrameow]

some jury rigged wiring in my W123 cluster started a fire which turned out to be a great thing. I ended up replacing the dash and the entire Interior and the car looks brand new,