DIY Oil Idiot Light Circuit

[brrian]

I'm converting my check engine light to an oil light. I had this done but got the circuit wrong & my light came on with pressure instead of going out. Below is my new circuit.

The check engine light (now oil light) has 12V power to one side.
with pressure under 4PSI, there's no power to the relay, so the light is grounded through 87A, and illuminates.
with pressure over 4PSI, power is supplied to 86 and 87, the relay switches to 87, and since there's 12V to both sides of the light, it doesn't illuminate.

Am I missing anything? Will this work?

 

[ELCAM]

No need for the relay. +12V to one side of the bulb and the other side grounds through the single terminal (warning light not gauge sending unit) oil pressure sending unit.

 

[brrian]

I'm using a 2-terminal switch to do this. it doesn't ground - it's just open or closed. Are you suggesting I use a single terminal sending unit instead of the switch? If so, I don't think I can because I don't have the room for it.

 

[ELCAM]

What you have there would work if 87 was not connected to anything.

There is another way to do this, the check engine light has a fixed ground and has the positive side switched by the electronic relay driven by +5V from the computer.

The way you have it will require you to cut the PCB and add a purple black wire (circuit 39) to power the light.

Let me draw something up. see if it would be easier.

 

[ELCAM]

No modification of the PCB required. Use existing Check engine light wire to gauge cluster from terminal 30.

 

[pagrunt]

To put a spin on this, why not use the Choke light? It does work as a oil light in the Chevy's & I would believe it would of been the same in the Pontiac's. My Monte is set up this way & so will Jr.'s when we do the gauge conversion.

 

[brrian]

In your diagram you have ground to the check engine light. The check engine light has 12V on one side (see circuit 139 below) and to operate it I have to supply ground to it, as the computer did. That's what makes it tricky, at least to me.

But how about this? See 2nd image below... I could use a single terminal oil pressure switch that's normally open and closes with pressure. When closed it would supply ground to the bulb. Simple. I have one of these switches but I'm not sure what pressure it opens & closes at so I'll have to test it.

pagrunt - I built a whole 'factory' choke circuit that uses the choke light. I swapped in gauges & wanted to keep an oil pressure light so the CE light was the only one available. I'm even going to modify it & swap in a red lens when I find one in a junkyard that'll work.

 

[bracketchev1221]

I would recommend something more than 4 psi. maybe 10-15. If you wait to 4 the engine probably already has broke. Autometer makes an 18 psi switch for their light. #3241. I ran a 30 psi switch in the race car.

 

[brrian]

The video below is the circuit mocked up with a grounded single-terminal oil switch. It's set up just like the check engine light with 12V on one side and the circuit providing ground, or not. And it works! I need a different switch because this one is activating at about 2PSI & that's too low. Per the internets, an ACDelco C8020 will activate at 5PSI & that's what I'll try.

bracketchev1221 - Buick 350's run low oil pressure & 15PSI or lower isn't out of the question while hot. The light is just for peace of mind & I've got a gauge to check.

 

[pagrunt]

I built a whole 'factory' choke circuit that uses the choke light. I swapped in gauges & wanted to keep an oil pressure light so the CE light was the only one available. I'm even going to modify it & swap in a red lens when I find one in a junkyard that'll work.

Was it set up like the full factory circuit with the two prong pressure switch & three wire plug? This would have the light blue going to the choke, green/white stripe going to the C100 then to the speedo cluster, brown/white also going to the C100 then to the CHOKE fuse itself.