1973 oil pressure gauge wiring

[hemmah]

I have a 1969T with idiot light oil pressure sensor. I bought a 1973 oil gauge with temp and pressure gauges. The 1973 oil pressure gauge has an + and G side plus ground connections. Does the 1973 oil pressure gauge G connection wire directly into the oil sensor as does the idiot light? So I would jump a wire from the idiot light oil sensor wire to the G connector then add +12 to the + connector? Correct.


Steve

[E Sully]

Yes. The G connects to the sending unit. On the 1973 the + terminal gets 12V when the ignition is in the run position.

[Walt Fricke]

Careful - the idiot light sender is just a normally on on/off switch. It is set to open at about 0.4 bar.
An oil pressure gauge requires a different sender - one which varies in resistance as oil pressure rises. And you can't confuse the two senders - the idiot switch is pretty small, while the pressure sensor is a much larger, can-like piece.

So are you disabling the idiot light in the instrument panel, and using its wire to connect to a newly installed oil pressure sender, and to your new gauge? That should work. The idiot light switch has M10x1.00 thread, as does one of the flavors of oil pressure sender, and you can screw the pressure sender in where the idiot light was.

Better, though, is to get one of the senders with two posts - an idiot sender and a pressure sender. Requires running an additional wire up to the dash.

But you don't want to "jump a wire" from the idiot wiring system over to the G terminal of your gauge. That wire has either 12 volts before there is oil pressure, or it is basically an open circuit. Running 12 volts through your new gauge from the idiot system is apt to damage your gauge, and if all you have in back is the idiot switch, you'll get that every time you turn the key on to run.

[hemmah]

Walt

Thanks for the explanation.

Yesterday, after reading about oil pressure switches and senders I figured I can not use the switch on the pressure gauge. I plan on not using the idiot light anymore and will use the existing wire and add a sender oil sensor.

Now to find the right oil sender sensor. Suggestions?


Steve

[Walt Fricke]

Your '73 gauges probably include a 10 bar or 150 psi oil pressure gauge. So buy a VDO oil pressure sender that is made for that pressure. Simple.

Your idiot light sender will have M10x1.00 thread. Be sure to purchase a sender with those threads. They also come with a larger metric thread, as well as a non-metric 1/8" NPT thread. You can use the NPT kind, but only if you also purchase a converter which screws into the metric fitting on your engine case.

I'd suggest, though, that you purchase the metric 2 terminal sender. That way you can have both oil pressure and a warning light from the same unit. No need to delete the warning light. Just run another wire for one or the other. Pretty simple to feed it through the tunnel.

If it were me, I'd use the stock wire for pressure, and the new wire for the idiot. That way, if you have chafe and the new wire grounds at some point in the future, you will see the idiot light come on. Looking at your oil pressure, you will see that you have good pressure. So you will have a pretty good idea that it is the idiot system acting up. But you can protect an extra wire at obvious chafe points with electrician's tape.