Possibly related instrument issue 300SD

[dmcginn2]

When I first bought my 83 300SD, the tach sometimes would quit working, so I figured I would be messing with that Amp at some point.

But then…I discovered it would begin working when I turned on the headlights….

Then about a year ago, my oil pressure gauge pegged out…so I figured it was the unit on the back of the oil filter housing. After replacing it, the gauge still does not work.

Fuel gauge goes wacky every once in a while…jumps around when it gets low. That might be the fuel sender…but before I go there...

What do you think, are they are all related to a ground issue in the dash?

[mach4]

Good chance - those are typical symptoms. Run a dedicated ground wire from the cluster to the chassis.

This is so common an issue, it should be a maintenance item everyone should do.

[dmcginn2]

Easy enough I suppose…

[charmalu]

Check the engine to body ground strap. It is on the driver side, bolted to the adaptor plate to body.

I had a problem with the 85 300D, the temp gauge would work ok, then suddenly peg out. turn off engine and restart, and it would work ok for a bit then start acting up. switched the wire plugs between the two senders on the side of the block, even replaced the temp sender.

Finally thought about the ground strap. removed it and it was the paint on the adaptor plate that was causing the problem. scratched it off, cleaned up both ends and all has been well.

I replaced the engine with a new one, and everything worked just fine for 30K miles, then the problem started. new engines look nice and pretty with the fresh paint, but it can cause a problem in this area. think I had a couple other electrical issues at the time also. they cleared up also.


Charlie

[dmcginn2]

Sounds like all easy checks.

Maybe I'll get on that tomorrow...

[gastropodus]

If you check the easy stuff, and still haven't found the problem, you might want to look at the speedometer cluster circuit board. My '86 W201 had some really, really weird intermittent problems, and it wasn't until I pulled the speedometer cluster and looked at the circuit board on the back that I discovered why: several of the solder connections had hairline fractures. I had to use a magnifying glass to see them, they were so tiny.

Once I re-soldered those connections all my electrical problems went away instantly.

Kurt

[dmcginn2]

Finally spent some time tinkering on this issue the other day after 8 months.

So to recap, I had already replaced the oil pressure unit on the back of the oil filter housing.

Took everyone's advice and tried a ground from instrument panel, still nothing.

Took the wire off the oil pressure unit, and grounded it...gauge goes down to 0 on oil pressure guage when ground is completed. So it looks like everything from the terminal back inside the car is fine.

Next step was to connect a wire from the engine to the frame to see if I could make it work...nothing. Granted it was only a piece of speaker wire with gator clips on either end...

So maybe next step is to put a bigger gauge wire from engine to frame to see what happens...

Any thoughts anyone?

[Phil]

Originally Posted by dmcginn2

Next step was to connect a wire from the engine to the frame to see if I could make it work...nothing. Granted it was only a piece of speaker wire with gator clips on either end...

So maybe next step is to put a bigger gauge wire from engine to frame to see what happens...

Any thoughts anyone?

Test it using one side of some jumper cables.