Hi,
I recently tried to fix my temp. gauge and after replacing both my coolant temp. sensor AND connector the gas gauge stopped working as well.
I read somewhere that a voltage regulator on the instrument panel might have gone out but i don't think my make and model of car has such a device.
I also read that perhaps the grounding was bad.
That's where i'm at a standstill. I tightened and checked all the connections on the circuit board of the instrument panel and now my only lead is to try to ground the whole thing. How is the grounding achieved for the instrument cluster on a 1988 749 GLe? Where are the connections located?
If anyone has any other tips that would be appreciated as well.

 

Hi again,
It would really help if someone just gave me the location of the grounding connections for the instrument panel on a 1988 740 GLE.

 

this is going by my 1992 740/940 wiring diagram.... 88 should be essentially the same.

everything on the instrument panel is grounded via a brown wire from connector D pin 3 to the ground rail thats under the fuse panel, this in turn has a black wire to the main ground for most of the dashboard stuff which is near the right A post, below and slightly forward of the passenger door lower hinge. its a 'comb' of like 2 rows of 4 each spades that are bolted to the firewall, and has a pile of mostly black and maybe brown wires coming off it. . instrument panel connector D is the 4 pin one right in the middle behind the speedo.

that ground 'comb' under the passenger door hinge grounds a LOT of stuff, my book lists climate unit fan, central electrical unit, bulb failure ensor, flasher unit, wiper intermitten relay, headlight relay, power sunroof, overdrive relay, central lock motors, power mirrors, power windows, load bypass relay, seat belt reminder relay, cigar lighter, radio & amp, glove box light, lh2.4 fuel pump, fog light switch, rear fog light relay, instrument panel, fuel gauge, electronic climate controller, turn signals, high beam bypass relay, dashboard lighting, vanity mirror, shift lock relay, rear window defroster switch, dash dimmer and clock adjust controls.

the speedo itself, the ABS controller, and the cruise control unit (if any) are grounded on the LEFT door side, also below and slightly forward of the lower hinge.

 

Ok, so i found the panel on the passenger side and checked the connection, no corrosion or anything so i doubt the problem is coming from there. As for the grounding under the fuse panel, i couldn't access or even see that.

Last night i went out and the speedometer also was acting funny. It was shaky and wouldn't even read my speed until 20 mph, and after that the shaking of the needle stopped and it would read accurately. Hmmm.
So let's see:

1. My temp gauge has been acting funny for month's, sometimes it didn't even register anything, and all of a sudden it would snap into place without any noticable pattern.

2. I replaced my coolant temperature sensor, and after i replaced my temp. sensor connector a few weeks later the temp. gauge stopped working altogether.

3. Next, after taking the electrical panel out to check the connections (i didn't know i was supposed to disconnect the battery at first, so i may have shorted it) my fuel gauge stopped working, in addition to my recently discovered speedometer problems.

So, i'm wondering what to do. I don't have a lot of electrical expertise, none at all really. I can't even read a diagram. So any help here please?
I don't know what to do.

 

the dashboard temp gauge uses a different sensor than the engine coolant temp sensor that the fuel injection and ignition controllers use. the dashboard one has a single yellow wire, the ECT for the ECU and ICU has two blue-red wires.

what electrical panel did you take out?

if you cant troubleshoot electrical problems, bring it to someone who can.

 

Not only do i lack the money for such a thing, i also want to learn how to do it myself.
I'm twenty years old and have enough practical skills that i managed to replace my headgasket alone. With you help i may manage to fix this problem as well.
Anyways, it's good to know that the temp. gauge uses a different sensor than the sensor, as i know that it's important for the functioning of the car to know the temp., whereas it is also important for me to know, but as i also fixed my overheating issue i can at least drive the car.
Anyways, thanks for the help.

 

And i took out the dashboard instrument panel.
What is an ECT, an ECU and an ICU?

 

the ECT is the Engine Coolant Temp sensor, its the two wire one I mentioned... these sensors are under the intake manifold... there's 3 positions with sensors, sometimes they are moved around, one is the antiknock sensor, one is the ECT, and the other is the temp gauge sensor with the single yellow wire.

ECU is the Engine Control Unit, its the computer that runs the fuel injection.

ICU is the Ignition Control Unit, its the computer that runs the ignition (spark). Both these computer modules are behind/under the glovebox on the passenger side of the interior.

 

Check this out.Electrical: Instruments

You're not alone when it comes to gauge problems.

 

Ya, i found that earlier and it offered good information which could theoretically help me fix it.
The real problem is that i don't know the first thing about electronics. I don't have any testing equipment either, so i can't very well learn anything without them.
However, i'm taking an electrical lab class at my local community college this coming semester and i'm hoping that i'll be more prepared to deal with my gauge problems after that. It's a good practical goal, an immediate project that i can enjoy on my way to greater problems using such skills.