'91 560 electrical issue. - PeachParts Mercedes-Benz Forum

Hit Man X · #1 11-12-2007, 10:36 PM

Well this is lengthy, so get your beverage of choice out.

Currently my '91 560 will start up and idle fine, BUT the fuel level, oil pressure, and coolant temperature gauges are all wacky. Fuel level reads empty (has new sender), oil pressure reads ~1.25 bar (on cold start), coolant (new sender) starts at 40°C then shoots up past 120°C within about 20-30 seconds of idle on cold start.

When I disconnect coolant sender, the gauge drops off to nothing. When I disconnect fuel, gauge drops to nothing, BUT! when I disconnect oil pressure it skyrockets to 3 bar.

This all started happening after I removed some crap wiring in the car. I removed the old cel phone that was installed (have done countless times). The aftermarket radio that was there did not work, so I reinstalled the factory Becker, again I know what wires went were on the factory harness, etc.

Also this is when I replaced the CIS sender, Aux fan sender, coolant temp sender, and the fuel level gauge. In addition to the motor mounts and the O2 sender.

Lastly I removed some aftermarket alarm that was installed. It had around six wires total. Of course I taped up what needed to be and heatshrunk the others. Again, I have done this in numerous vehicle I own/have owned.

NOW - I have unplugged about everything I can find under the dash (both sides) and removed every fuse/relay I could minus the No 6 that ran the left side gauges... NOTHING changed. I unplugged the senders as stated above. Disconnected the O2 sensor, disconnected fuel level, CIS, fan, etc, etc, etc

How many body grounds are there? Maybe I messed one up when doing motor mounts?

When going to reinstall the gauge cluster (I had to tape up the ignition switch wires) I missed putting the clock wire to the pin and accidentally hit the back of the cluster with the 12V. It was for a brief instant, but could that have caused my issue?

I don't have another '86+ gasser cluster handy to test so that's the only thing I have not tried at this point. Everything was fine until this and I'm sure it's something simple I am overlooking/not thinking about. Is it possible the plug to the left gauge pod can spin despite the half moon keyway it has?

Is there a way to test that gauge cluster? The grounds behind there all seemed fine. I pushed and pulled on them lightly with no issue. The ones near the battery appear okay also.

Sorry for the length guys but I had to try to explain all I have tried up to this point. If I have forgotten something, point it out and I'll see if I haven't tried it or not yet.

Brian Carlton · #2 11-12-2007, 10:51 PM

Find the 8 pole plug for the cluster.

Find socket #3.

Check for continuity to ground. If you don't have full continuity (zero ohms)........that's your problem.

Also, is the high beam indicator light somewhat weak........or not illuminated at all (check it at night)?

Hit Man X · #3 11-13-2007, 08:58 AM

I'll check the headlight indicator, but that reminded me that when I tried the lights the gauges went crazy even more. Still the same three.

So if I do not have proper ground, do I begin to trace where that wire leads?

Brian Carlton · #4 11-13-2007, 09:06 AM

Quote:

Originally Posted by Hit Man X

I'll check the headlight indicator, but that reminded me that when I tried the lights the gauges went crazy even more. Still the same three.

So if I do not have proper ground, do I begin to trace where that wire leads?

.........one step at a time.........perform the test first.

Hit Man X · #5 11-13-2007, 09:48 AM

LOL. Have go pick up a fuse for my analog meter. Will test today.

david s poole · #6 11-13-2007, 09:54 AM

i have resolved this issue in the past by running a separate ground from the metal on cluster to the main grounds right behind the cluster.

Hit Man X · #7 11-14-2007, 10:50 AM

Pin three grounds properly

Read 0 ohms.

I flipped the lights on with the vehicle off and the fuel level sender shot off to the right.

I tossed in an alligator clip as David stated, fixed everything. This ran from a stud on the cluster to the common ground point behind the dash.

SO I'm very close.