Speedo was just re-installed and now the fuel gauge AND the temp gauge peg out with the tachometer.

In other words, when the engine is revved, the fuel and temp gauges increase, let off the reves, gauges come back down. They oscillate at higher speeds. Also, the seatbelt light comes on intermittantly and the glow plug and warning lights on the lower left dimly glow when the seatbelt light decides to come on.

ALL of these worked fine (except the odometer, decided to fix that, got that done, but now with installation, I get all these bugs??)

Seems like a ground problem, but nothing else was changed, just speedo out, fix, re-install, now these weird bugs.

Anyone seen this before? Got a hunch? I'm all ears.

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1984 300D Turbo - 4-speed manual conversion, mid-level resto

1983 300D - parts car

1979 300TD Auto - Parts car.

1985 300D Auto - Wrecked/Parts.


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"If you don't know where you are going, any road will get you there". Lewis Carrol

I had some really strange guage happenings once after odometer work. They would jump forward and backwards and all over the place. Turned out that the metal surrounding the instrument cluster needed a better ground. It was intermittant based upon vibration. I drilled a little hole in the metal on the cluster and ran a wire to a ground. Fixed!

Don

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DAILY DRIVERS:
'84 300DT 298k (Aubrey's)
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'96 Passat TDI 237k (Don's
'84 300D 211k Mint (Arne- Undergoing Greasecar Conversion)

SOLD:
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Don,

That sounds about right to me. Seems like a ground problem. I'll try that.

Worked Mil contract in the early '80's, tape drives for tank control systems, had this really weird problem that was LESS than intermittant, logic would re-zero randomly. Turns out, after THREE WEEKS of watching the scope, that the friggin' instrument BULBS were drawing too much current and would occasionally bring the voltage below threshold for the logic and it would "lose it". If we'd just used LED's......

__________________
1984 300D Turbo - 4-speed manual conversion, mid-level resto

1983 300D - parts car

1979 300TD Auto - Parts car.

1985 300D Auto - Wrecked/Parts.


=========================

"If you don't know where you are going, any road will get you there". Lewis Carrol

It sounds more like a zener diode type problem to me... something which is designed to limit the upper voltage reaching those items is blown... may be a resistor/capacitor filter circuit or the likes..

Sounds familiar.

A long time ago on a planet far, far away I worked for an outfit that designed, built and installed industrial security systems...door monitoring, locking, surveillance etc... all of our stuff was made up of separate PC boards with their own little TTL circuits that sat in 19" rack mount hardware which was usually sitting on top of the security console/cabinet that we would also build for the client.

On one contract, the console/cabinet was too big (300+ covered doors in 4 or 5 Optima enclosures) to set up in our office so we only built and bench tested one at a time. They all worked OK in the shop so we shipped them to Houston and drove down to do the install and hook up.

It took about three days to do the interface wiring and some other niggling stuff. Finally, the thing was ready to go...

In it's delivered configuration, the system had a master lamp test button that enabled the operator to make sure all the indicator bulbs (one red and one green, and the weren't LEDs back then) functioned properly...unfortunately, because of it's size, the system had never been tested at our shop in that condition.

After we'd done all of the functional testing, Art pressed the lamp test button at which point instead of lighting up like a Christmas tree, the whole system momentarily went dark and came back to life with doors waking up in random states. Not good.

After much gnashing of teeth and pulling of hair, we determined that the instantaneous inrush current of those 600+ 12V incandescent bulbs was somewhere in the order of 90 amps....waaaay beyond the capabilities of that poor little HP power supply and the system's 10ga cabling.

We eventually solved the problem by wiring the lamp test to a rotary selector that only allowed one bank of bulbs to be tested at a time.

__________________
Never a dull moment at Berry Hill Farm.

Got any idea WHERE I might start looking? I guess it's another speedo pull for me, might be on those control boards. I'll try a good ground first though.

__________________
1984 300D Turbo - 4-speed manual conversion, mid-level resto

1983 300D - parts car

1979 300TD Auto - Parts car.

1985 300D Auto - Wrecked/Parts.


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"If you don't know where you are going, any road will get you there". Lewis Carrol

TomJ,
Every time I've pulled the cluster, I've always thought that the way that round plug attached was pretty cheesy. I can't remember the exact wiring but, if the ground comes off there (I guess it has to), I'd be looking at it really close.

__________________
Never a dull moment at Berry Hill Farm.