The car came with two aux gauges that never worked, oil pressure and temp, connected to a VDO sender in the engine area. They would just bounce around all the time. The sender was loose in the holder so I tightened that a bit and then the pressure gauge started working, but not the temp. Now the pressure gauge just pegs at max as soon as I turn the key and gets stuck. I have to thump it to go back to 0 after I shut it off. The temp gauge is still no go.

Everything thing on this car is a new learning adventure. Help please... wiring issue, sender unit? Where to start?

Oil Temp and Oil Press come from different sensors.
The Oil pressure sensor is probably the sensor you tightened up, the mount needs to be secure and grounded or the gauge won't work.

The Oil temperature sensor is on the bottom of the engine and the wire comes up through the engine shelf below the battery.
Oil on a 914 is slow to warm up, so the gauge may look inop when it just hasn't warmed up enough to show on the gauge.

Good luck
Jim

Any way to test either sensor?

Measure resistances but I don't know the specs.
For Temp compare resistance both hot and cold
For press compare resistance with engine running and without running.
To verify either use a separate test gauge and measure actual Tempo or Press.

Jim

I see the VDO sender all over the place for sale, I never see a bracket for it. I see some are screwed directly into an engine where a sensor would go, mine is on a remote hose and then to a bracket that does not fit right. What bracket are these supposed to be in? Mine is very loose in the bracket.

Sender on remote hose is the better soution vs. mounting on engine on cantilevered brass tubes that will eventually fail. Stay with the remote hose.

There is no purpose built bracket offered by VDO that I've ever seen. This is your task with aftermarket parts. It's up to you to modify them to your purpose.

Without knowing the ohm spec, you can probably ohm it, then hit it with a heat gun for a minute and re test it. I believe the resistance should change. Just be careful not to melt anything.

Or disconnect it and connect an ohm meter and start your car. You should be able to watch the resistance change as your car warms.

Skip the heat gun and use boiling water. Verify the temp with an 'instant read' kitchen thermometer. You won't melt anything.

FOR OIL TEMP there are 2 different sensors,
short one for 120 or 150 Degree C
and long one P/N 039 919 260 for 200 Degrees C used on 1973 & later cars

My 1976 has the oil temp in the combo gauge along with fuel level & not on an aux gauge and it reads OK using the long sensor.

Is that really 200 C? That's 392 F. Pretty hot for oil temp.

That's the MAX the sender id capable of, not expected oil temp's

Try replacing the temp wire from the sending unit back to its connection under the battery tray. That fixed mine!

Thanks for the tip, I was about to connect an oil pressure gauge to a brass extension with a couple ell's and keep the idiot light. 1/8" brass does not have much strength.

Got a temporary ground worked out for the bracket. Things are better and worse. The light on the dash is working, goes on and off. The pressure gauge side of the VDO sender has an issue. The gauge is pegged as soon as you turn the key, never comes down and has to be wacked to drop back after the car is turned off. This happens even with the wire disconnected from the sender. How can I test the gauge to see if it is bad? What else would cause the gauge to max out on start?

Got the temperature gauge working, it was a failing connection under the battery tray. broken wire inside a tape joint. Warmed the engine up and saw it climb to 180 just to check it.

What would make the gauge peg as soon as the key is turned? Is that a voltage short? If I pull the + wire it does not do that but wont work correctly. What am I looking for?