That's the last line in the chain of power to the choke assist heater. It allows power to the choke assist only when the engine has oil pressure.

So once there's enough pressure one of the other connectors will have power? Right now the only power at the oil pressure sending unit is coming in from the white wire from the dash...
If the other two connectors don't have power at any time does that mean the sending unit is bad?
I don't remember what else was connected to the oil sending unit, I removed a bunch of rat chewed wires that were there for the smog components that I removed...

It's been a VERY long time, mebbe 35 years since I messed with it. I think there's switched power coming into the unit, power to the choke assist and metered power based on oil pressure to the gauge. Somebody with fresher memories will be around to correct me. Three wires is all I recall.

You are correct, one terminal is the signal to the oil light. With the key on but the engine off it should ground and show the light as lit. Of the remaining two terminals, one should be hooked to switched 12v. The remaining terminal goes to the compensating resistor mentioned above and is only hot with good oil pressure. This is to prevent the choke from heating up with the key on but engine off.

it's amazing how close the dash controls look between the two years.
if i'm thinking correctly [HA ! ] i believe those are vacuum operated.
in fact, that control [or one almost identical] was used on 74-78 C bodies. i scrapped a few of those many moons ago.

Ok so one of the remaining two connecters gets a "switched" 12v wire and the other to the choke resistor...
What's a "switched" 12v?? Is that just a hot wire that's only hot when the ignition is on?

Was the motor running and did it have oil pressure? If it was not running, or was running and did not have oil pressure, the switch would not provide the voltage through it. The switch would be working correctly.

However, if the motor was running and did have oil pressure, the switch is defective.

oil pressure is a strange thing. Most people have the understanding that motors need a certain level of oil pressure to keep running, and to a point, that is correct, but, The original motors from years ago ran without a pressurized oiling system. In the old days, motor lubrication was done mostly by splash. There was oil in the pan, and the crankshaft would make contact with it (or swing close enough to force some of the oil in the pan out of the pan), and kick the oil up into the motor to lubricate the high wear contact points. That system was used pretty effectively up through the 50s in some motors, but as the power levels increased, it was discovered that pumping the oil through the motor was more efficient and the pressurized system became the normal. These days, many of the small one cylinder motors (like your lawn mower or weed eater) still use the splash system of motor lubrication, but nearly every multiply cylinder motor uses the pressurized system. Generally speaking, a pressurized system requires a minimum amount of pressure to keep the motor operating because most high wear contact areas are no longer open enough to get much oil splash, and most crankshafts no longer make contact with the oil in the pan (it takes away HP). When the pressurized motor does not maintain enough oil pressure, the high wear areas don't receive enough oil to properly lubricate the critical parts and the contact surfaces can wear extremely fast. as one might imagine, those wore out high contact parts begin to fail and those failing parts stop the motor from running, either by a slow grinding halt, or a fast explosion. The time frame for that to happen largely depends on the original clearances the motor was built to. The more modern motors are built to a tighter tolerance and the failure often happens sooner then the older looser tolerance motors. Also, the minimum oil pressure needed varies between the manufacturers, and even between specific motors within the manufacturers.

Standard operating procedure for me was to always run a mechanical oil pressure gauge on any motor I had any question concerning oil pressure. The old Mopar motors will run a long time on pretty low oil pressure, I've seen them run for years with less then 5psi at an idle when at normal operating temp but that low oil pressure usually jumps up as the rpm increases. Chrysler considered 10 psi per 1,000 rpm to be normal and adequate for performance motors.

The down side of all this is that some of the electric sensors won't function well with low oil pressure, many won't function well below 10 psi. If the motor doesn't have enough oil pressure to make the sending unit happy, it won't function. You could pull the power wire from any ignition powered wire (on or off with the ignition switch) for your choke rather then off the oil pressure switch, as long as the choke wire runs through the little procyclin terminal thing before it is connected to the choke spring. Gene

Just another thought, does your van have a gauge for the oil pressure, or does it just have an oil light? The sending unit for the light is different then the sending unit for the gauge. The light sending unit should just be an on/off switch but the sending unit for the gauge is probably a varied resistance switch. For what you are doing, I would think the sending unit for the light would work better, but not sure how it would work with a gauge, could make it max out.

Yes, install the fittings and tubing for the mechanical oil pressure gauge into the place the sending unit was originally in.

If you want to get fancy, that hole in the block where the sending unit screws into is a 1/8" pipe thread. You can get a short 1/8" pipe nipple (the pipe nipple can be longer or shorter to clear the back of the intake, as needed) with an 1/8" pipe "T" (the pipe "T" can be screwed onto the nipple any way that makes the best clearance) and install both the sending unit, and the mechanical gauge. Use the Teflon tape on all the threaded ends and be sure the pipe and the "T" are tight before installing the sending unit and the fittings for the gauge.

Just another thought, does your van have a gauge for the oil pressure, or does it just have an oil light? The sending unit for the light is different then the sending unit for the gauge. The light sending unit should just be an on/off switch but the sending unit for the gauge is probably a varied resistance switch. For what you are doing, I would think the sending unit for the light would work better, but not sure how it would work with a gauge, could make it max out.

Yes, install the fittings and tubing for the mechanical oil pressure gauge into the place the sending unit was originally in.

If you want to get fancy, that hole in the block where the sending unit screws into is a 1/8" pipe thread. You can get a short 1/8" pipe nipple (the pipe nipple can be longer or shorter to clear the back of the intake, as needed) with an 1/8" pipe "T" (the pipe "T" can be screwed onto the nipple any way that makes the best clearance) and install both the sending unit, and the mechanical gauge. Use the Teflon tape on all the threaded ends and be sure the pipe and the "T" are tight before installing the sending unit and the fittings for the gauge.

You are correct, one terminal is the signal to the oil light. With the key on but the engine off it should ground and show the light as lit. Of the remaining two terminals, one should be hooked to switched 12v. The remaining terminal goes to the compensating resistor mentioned above and is only hot with good oil pressure. This is to prevent the choke from heating up with the key on but engine off.

I think what happened is when my tranny went out last year I had it parked for months and some rats made a home of the engine bay and they chewed the wires. Before I had realized the damage caused by the rats I turned the ignition on and burnt a bunch of wires and that is when the oil pressure switch got fried!

Some varmint chewed through the upstream and downstream O2 sensors (and two ignition wires) on my wife's Town and Country and shorted the PCM/ECM when I went to move it. Had to finally replace it with a reman $270 PCM/ECM and another $250 for two O2 sensors and a complete set of new ignition wires later fixed, not happy with mice, rats and varmints and soy base insulation. Should make the wire insulation out of RAT POISIN if you ask me Die-O-degradable insulation think I'll patent that