Oil/Choke dimly lit?

[Homie_Telefrag]

Past few days the GN hasnt been wanting to fire on the 1st time. Then I noticed leaving for work early in the AM that the Oil/Choke light was on, but just really dimly lit. Ive had this issue before, so I figured it was the oil pressure switch. I replaced it and it now starts up fine, but now the Oil/Choke light is on still. Oil is full, nothing seems to be amiss or changed.... Any of you guys have any ideas? -Ben

 

[salvageV6]

Unplug the connector and keep it safely away from the motor and moving parts and see if it is still lit when idling.

Always verify oil pressure with a gauge if it lights up, but it's probably just the wiring or sender.....

 

[Homie_Telefrag]

It doesnt have a connector? Just has 3 spade connections on it - same with my 87 Turbo T. Guessing these break often and never get replaced? Its intemittent when its doing it now, but it comes on so faint/light its hard to see it during the day. Maybe a wiring issue somewhere else or....?

 

[salvageV6]

Yeah the rubber end melts off, 3 spade connectors should work fine if they only touch the switch contacts.....

The light illuminates when the oil pressure switch grounds the signal wire which is below 4 psi.

If you pull the signal wire off the oil pressure switch you'll know if it's the switch itself or wiring/dash bulb socket that's partially shorted, if fully shorted it will light up brightly.

 

[aminga]

And you have verified the oil pressure with a gauge?

 

[earlbrown]

Does the oil light shine bright during the bulb test?

 

[Homie_Telefrag]

Yeah the rubber end melts off, 3 spade connectors should work fine if they only touch the switch contacts.....

The light illuminates when the oil pressure switch grounds the signal wire which is below 4 psi.

If you pull the signal wire off the oil pressure switch you'll know if it's the switch itself or wiring/dash bulb socket that's partially shorted, if fully shorted it will light up brightly.

Which wire of the 3 is the signal wire? I will check this later in the week when I have time.

Does the oil light shine bright during the bulb test?

Actually, now that you mention it, it doesnt. You are referring to when you first have key on before start and all the lights on the side light up yes?

 

[earlbrown]

Yep. It should be lit up until the engine makes 4PSI 'o oil pressure.

 

[Homie_Telefrag]

Yep. It should be lit up until the engine makes 4PSI 'o oil pressure.

So would that mean that its getting 4PSI oil pressure at keyturn somehow or a wiring issue...?

 

[Pronto]

Test it with a manual oil pressure gauge and find out.

 

[salvageV6]

Middle terminal on the oil sender is the switch, it is terminal B, with car off it should read low ohms or a dead short 0 ohms to the engine ground with the car off with an ohmeter.

Tan is the wire color.

Gray is for the fuel pump +12 feed switched circuit.

If you short the tan wire to ground the light should light up brightly with the key in the ON position, no need for car to be running.

Next time you see it light up dimly, shut the car off and verify it's still on dimly with the key in the ON position, then unplug the tan wire and see if it's still on dimly.

Oh and before all this testing make sure the oil pressure is okay with a mechanical gauge.

 

[Homie_Telefrag]

Middle terminal on the oil sender is the switch, it is terminal B, with car off it should read low ohms or a dead short 0 ohms to the engine ground with the car off with an ohmeter.

Tan is the wire color.

Gray is for the fuel pump +12 feed switched circuit.

If you short the tan wire to ground the light should light up brightly with the key in the ON position, no need for car to be running.

Next time you see it light up dimly, shut the car off and verify it's still on dimly with the key in the ON position, then unplug the tan wire and see if it's still on dimly.

Oh and before all this testing make sure the oil pressure is okay with a mechanical gauge.

Okay, I shorted the middle wire to ground and the light didnt come on still. But now, the car wont start.

 

[v6turbo87]

Remove the short. Turn the key to on and listen for the fuel pump to turn on for a few seconds. If it doesn't check your fuel pump fuse.

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[Homie_Telefrag]

Pump was fine - injector fuse was blown. I take it I was NOT to ground the middle wire but one of the other 2?

 

[salvageV6]

Did you do this first test first?

" Middle terminal on the oil sender is the switch, it is terminal B, with car off it should read low ohms or a dead short 0 ohms to the engine ground with the car off with an ohmmeter. "


Was it a tan wire you shorted?

 

[salvageV6]

The pink/blk wire is power +12 to run the fuel pump if over 4 psi. oil pressure is reached when cranking the engine in case the fuel pump relay fails, the car will still run, just start a bit slower.

The gray wire goes to this prime circuit for the fuel pump it's the output of that switch.

The wire for the light is tan colored you may need to look further back on the harness for a clean spot to tell the color.

The tan wire goes on terminal B of the sender, that terminal should read shorted to the Metal case of the sender or engine block/battery ground when the car is OFF and key is OFF, so that's a simple test to do to find the right terminal for the oil pressure light switch. Pull the wire off and measuure the terminal to a good ground point with an ohm meter low scale.

One switch in the sender closes BELOW 4 psi. oil pressure for the light warning circuit, which shorts one terminal to ground via the sender threads in the brass block. That's why it lights up brightly in the key on test prior to starting since there's no oil pressure yet in the motor.

One switch in the sender closes ABOVE 4 psi. oil pressure, to provide +12 to the fuel pump gray prime circuit wire.

It's not hard to test the sender with an ohm meter.

 

[Homie_Telefrag]

The pink/blk wire is power +12 to run the fuel pump if over 4 psi. oil pressure is reached when cranking the engine in case the fuel pump relay fails, the car will still run, just start a bit slower.

The gray wire goes to this prime circuit for the fuel pump it's the output of that switch.

The wire for the light is tan colored you may need to look further back on the harness for a clean spot to tell the color.

The tan wire goes on terminal B of the sender, that terminal should read shorted to the Metal case of the sender or engine block/battery ground when the car is OFF and key is OFF, so that's a simple test to do to find the right terminal for the oil pressure light switch. Pull the wire off and measuure the terminal to a good ground point with an ohm meter low scale.

One switch in the sender closes BELOW 4 psi. oil pressure for the light warning circuit, which shorts one terminal to ground via the sender threads in the brass block. That's why it lights up brightly in the key on test prior to starting since there's no oil pressure yet in the motor.

One switch in the sender closes ABOVE 4 psi. oil pressure, to provide +12 to the fuel pump gray prime circuit wire.

It's not hard to test the sender with an ohm meter.

The wire colors I got are oil, oil, and oil. I just have 3 spade connectors so if Im staring at the oil pressure switch like this ( | __ | ) I took the middle one and shorted it to ground. The light didnt light up bright or change - still on dimly lit. I cant find the right fitting to test oil pressure with my gauge, so thats out of the Q till I grab a new fitting. I'll keep you guys posted I guess.... -Ben

 

[salvageV6]

If the wires are hooked up incorrectly it would explain your dimly lit bulb.

You need an ohm meter to test the switch with the car off, metal case of oil pressure switch to the three terminals with the wires off them.

If you don't get a good reading to ground on the one terminal make sure there is no Teflon tape on the NPT threads for the oil pressure switch into the brass block.

The B terminal that reads shorted to the case goes to the Tan bulb light wire.

The pink/blk and the gray wires will go to the other two terminals and it doesn't matter which one goes on which terminal out of A and C that are left.

And if you shorted the fuel pump prime circuit and blew the FP/INJ fuse and the fuel pump still worked I would assume that circuit has been modified as well?

Normally that FP/INJ circuit is used to trigger a hot wire relay and will kill the fuel pump when that fuse pops....???

 

[Homie_Telefrag]

I have a hotwire kit if that explains why the fuel pump was still running but the injectors weren't firing. The car was originally a 85 hot air GN, so theres plenty of wire butchery under the hood and there are a few different wire colors here and there from factory... Keep you guys posted... -Ben