Hi Guys. I have just installed a 4 brl Rochester with elec choke on my rebuilt 400 engine. See link (400 g block build with pics). I have I think installed it correctly using "Joes" wiring diagram (link below). The problem I have is that the Oil pressure light on the dash stays illuminated when I switch the motor off and take the keys out. It switches off when the motor is running. Can anybody tell me what I have done wrong.





https://classicoldsmobile.com/forums...ess-switch.jpg

 

Without knowing exactly how the oil switch pins are configured, I would guess you have the power and choke wires back-wards. The power wire is supplying power to the oil light, it grounds through the ignition switch with the key off. Pretty sure one of the pins is normally open, the other is normally closed. When the engine is running the normally open pin is connected to the common wire. Just a guess.

 

The center terminal should be going to the OIL light.

If it is, try swapping the other two terminals with each other (I don't know the exact pinout of this sender either, though I know it is available on line).

- Eric

 

Ok Thanks Ill try.

 

Shouldn't the 20A fuse be on a keyed source?

 

That's how I would do it, but since the oil pressure switch is closed only when the engine is running, it should be OK the way the schematic shows. It was probably connected to the alternator to keep the wire length short and the wires fairly hidden.

 

One terminal should be normally open and the other normally closed with a common terminal. I thought the oil pressure switch is open when the engine is running. When the pressure drops it sends a ground to the light.




I like this way with a relay better.

 

On those schematics it shows 2 points of contact at the rear of the Alternator. 1 - to the generator light, 2 - to the battery, choke coil. If you look at my pictures there is only 1 point of contact. Am I missing something?????

 

The schematic shows three wires coming from the alternator:
One to the battery
One to the regulator or the ALT light
One to the regulator or the sensor point at the horn relay.

- Eric

 

If you used the normal Standard Motor Products PS64 switch, the center terminal should be grounded when there is no oil pressure and open when pressure is above 4 psi or so. I would get an ohmmeter and check that first (with the wire to the idiot light disconnected). I would also check the wire to the light. With it disconnected from anything, the OIL light should be off with the key on. With the wire grounded the light should be on.

The other two terminals on the PS64 are simply an on/off switch. The two terminals are open when there is no oil pressure and connected to each other above 4 psi.

Your alternator connector appears to be missing the wire to the GEN light. That is unrelated to the choke/oil light problem.

 

Okay, so with Joe's definitive information (sorry, I was too busy to look it up myself), we know that if your oil pressure gauge is connected to the center terminal, it is connected correctly.

As Joe suggests, you should troubleshoot the affected parts of the circuit: the center terminal should be grounded with no oil pressure and open with the engine running, and the oil light should come on if you ground it with the ignition ON, and turn off when not grounded.

That being said, you describe the oil light turning off as it should when you have oil pressure, but not turning off when you switch the car off.

Since the oil pressure light gets +12V from the ignition switch RUN circuit when the car is on, and lights only when grounded, and since there is no power to that circuit with the engine off, having the light glowing with the engine off and the pressure switch grounded would imply that you still have power to your gauges circuit, even when the ignition switch is off, which is a problem that has nothing to do with your electric choke.

If you had connected the oil light to the wrong terminal, then nothing should happen when you turn off the engine, because the switch between the two other terminals should be open.

Bottom line: Unless there's something important you're not telling us, the only way that your problem could be happening is if you have a wiring problem elsewhere in the car.

- Eric

 

That all makes sense. I will check all relevant wiring and get back to you guys. With me removing the engine and reinstalling it, I may have either missed something or reconnected something incorrectly.
Cheers for all the advice.

 

With the key off and the oil light wire to the 12v it can back feed a ground through the pink wires. I could not find a description that stated the center post is an isolated pressure generated ground. Thank you Joe for sharing that info as now the circuit makes sense.

 

Ok guys I feel like a real goose. I changed the wires for the choke around on the ps64 and guess what, it works just fine. I'm so embarrassed, I do apologize for my stupidity.

 

Glad you got it fixed! I needed a review on this switch anyway.

- Eric

 

Same here. Note to Joe, nice setup, I'm going to file that one.

 

I did the same exact bone head move! But quickly realized I had the two wires switched and made the swap and it all worked out well. So dont feel alone