I'm at the point that I will be reinstalling my gauges here pretty soon.

Is there a way to test these not to mention get everything hooked up the right way?

The 912E came with from left to right:

1 - Fuel gauge
2 - Oil Temp
3 - Tach
4 - Speedo
5 - Clock

I am making several changes, but want to be able to test the gauges before installing.

1. Eliminating the stock fuel gauge and using a VDO mounted in the center gauge cluster with a CHT & Clock. The CHT & Clock are no brainers, and the fuel gauge is a new gauge and known to match the sender. How do I test the sender? Make sure I have the right wiring?

2. Adding a 911 Style Oil Temp & Pressure gauge. I did add and/or swap put the senders to match the gauge, will run a fresh wire for the pressure gauge, and will move the wire from the temp sender to the new gauge, but how do I test the gauges themselves?

3. TACH - How can I tell if my TACH is good? Battery? volt/ohm meter? potentiometer?

4. SPEEDO - Same as above, how can I tell if it is good?

I'm going to assume the idiot light circuits will still work, but I have to say that the gauge cluster and wiring is just out of control.

NOT feeling a warm and fuzzy about this...... I have been as perplexed at the over complexity of the wiring choices of this car as I was impressed and amazed at its mechanical simplicity and brilliance...... Just 5 minutes dealing with the insane routing of the front parking/head/directional is enough to convince that the communists must've infiltrated Stuttgart on the day they drew up the 911 wiring harness.....

The oil temp and pressure gauges just read resistance. They might go the opposite directions? Anyway, hook them up to power and ground, and hook the sender terminal to a 0-1000 ohm potentiometer that then goes to ground. Turn the knob on the pot and the needle should move.

You can also just power and ground the gauge, then short the sender wire to ground then disconnect it. Should peg the gauge in each direction with those two steps.

The tach would be tested with an electronic signal generator. If you're asking, you almost certainly don't have one.

The speedo, if it's electric, also needs a signal generator. If it's mechanical, then you can plug a square-ended cable into the place on the back that the speedo cable threads on, and spin it backwards with a hand drill.

--DD

Thanks Dave,

Funny thing is I do have a signal generator, built it in a prior life when I thought I was going to be an electrical engineer. Built it the same time I built my 30 Amp variable voltage DC power supply that I have used non stop for DC voltage on my bench since I built it in.....gulp 1980...... The signal generator is in a box somewhere.... I built it to test filament/cathode bulbs for old radios and TV's...... I actually also have an old style TV tube regenerator, made a ton of $$ in HS & college fixing peoples TV's by 'tuning up' the tubes. My how far we've come.

I also have a 10amp potentiometer I was going to use for a variable fan speed control when I was playing around with 12V heater boxes.

Will have to sort out the speedo and tach when I get the car running. Will make sure my timing light has a built in tach so I can control engine speed for break in.

Hah! Good thing I said "almost certainly"!!

Feed the tach a 12V-0V square wave. The points signal is notoriously noisy, but I think a 12V wave should get the tach to move.

--DD

I use an Accutach Box and run it off an old PC w/ USB and use a free program called SigJenny for the signal.
SigJenny can vary the pulse width to test different points dwell. Sweet.

The Accutach was less then $100. I was doing some british tachs so I got the one that can drive Smiths as well (current driven).

Works great.

I always prefer to test the sender with the gauge it will be used with. Less surprises that way.

Oil pressure - plumb the the sender to an air compressor and test the gauge. Works for pitot tube boat speedos.

Temp gauges - I mount the sensor in a chunk of aluminum and put it in my PID controlled oven w/ accurate temp probe also in the chunk.

I also like to power the sensors and gauges with a variable power supply so I can record the readings at 12v up to 13.8v. A big difference in some gauges !

Just did the gauges/senders for a soon to be very nice Pantera for a friend.
Decided to test my '86 Donzi and found the coolant temp sender was a BBC unit and not the Gaffig. It was way off.

Have fun

Actually I dont think a 12VDC square wave will work.
The output of a MSD "tach" signal is a nice clean 12VDC square wave and the tach doesnt do anything when connected to that.
The "tachadapt" devices by MSD take that square wave and turn it back into a simulated version of the coil (points) signal and feeds that to the tach.
That signal can be up to hundreds of volts in spikes so I dont know what voltage level the tach actually triggers at.

Hmm... I think that's right (now that you remind me!) for the stock four-cylinder tachs, but not for some of the later six-cylinder ones? I don't remember the cutoff though.

--DD