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Discussion Starter #1
:cool: I've been trying to figure out why my oil and gen dash lights went out a few years ago? I'm working on the oil dash light first and find the wiring a little confusing. I replaced the bulb with a fresh T57. Now when I turn the ignition switch on both the TAN and DK BLUE wires are hot? I have a black /white wiring diagram and the DK BLUE looks like its a ground at the oil sending unit. I'm not sure how the light used to work because I don't have a oil sender unit. I have always had a set of Autometer gauges and the oil pressure gauge is hooked up with the copper tube in the rear of the engine near the dist. Sorry for rambling on. I know the Tan wire gets hot off the ignition switch. The question here is why is the DK BLUE wire hot with the ignition on also ❓
 

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Trifive Automotive Electrical Wiring Expert
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:cool: I've been trying to figure out why my oil and gen dash lights went out a few years ago? I'm working on the oil dash light first and find the wiring a little confusing. I replaced the bulb with a fresh T57. Now when I turn the ignition switch on both the TAN and DK BLUE wires are hot? I have a black /white wiring diagram and the DK BLUE looks like its a ground at the oil sending unit. I'm not sure how the light used to work because I don't have a oil sender unit. I have always had a set of Autometer gauges and the oil pressure gauge is hooked up with the copper tube in the rear of the engine near the dist. Sorry for rambling on. I know the Tan wire gets hot off the ignition switch. The question here is why is the DK BLUE wire hot with the ignition on also ❓
The sending unit supplies the ground. Without a ground, you will see 12 volts on both terminals of the bulb. Ground the blue wire and the bulb will light up and the blue wire will be zero volts. The oil pressure switch is closed when the engine is off and grounds the bulb. The pressure switch opens when pressure is built up and turns the light out.
Same with the gen light, the voltage regulator supplies the ground until it starts charging, then the ground goes away (actually rerplaced with 12 volts) and the gen light goes out.
 

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If your blue wire is going to a single pin oil pressure switch it will be grounded thru engine block thru sender unit and light will turn on until oil pressure is achieved and then the circuit will open and turn light off. You can just ground the blue wire and light should come on to check light if you don't have a sender unit . Oil pressure sender unit are different for light and gauges
 

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The sending unit supplies the ground. Without a ground, you will see 12 volts on both terminals of the bulb. Ground the blue wire and the bulb will light up and the blue wire will be zero volts. The oil pressure switch is closed when the engine is off and grounds the bulb. The pressure switch opens when pressure is built up and turns the light out.
Same with the gen light, the voltage regulator supplies the ground until it starts charging, then the ground goes away (actually rerplaced with 12 volts) and the gen light goes out.
Thanks for the reply. I'm usually pretty good at basic electricity. Now the other end of the DK BLUE wire is in the engine compartment and of coarse it's hot with the ignition on. To ground this DK BLUE wire to make the light go on would cause a short in my mind? For some reason I can't wrap my head around it. I thought I had a crossed wire for sure .
 

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Discussion Starter #6
If your blue wire is going to a single pin oil pressure switch it will be grounded thru engine block thru sender unit and light will turn on until oil pressure is achieved and then the circuit will open and turn light off. You can just ground the blue wire and light should come on to check light if you don't have a sender unit . Oil pressure sender unit are different for light and gauges
Thanks for your reply. Is there a way to hook up single pin oil pressure switch along with my auto meter fitting on the rear top of engine ?
 

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Thanks for your reply. Is there a way to hook up single pin oil pressure switch along with my auto meter fitting on the rear top of engine ?
Just put in a tee fitting so you can use both sending units. I did this when I had a mechanical oil pressure gauge so the gauge and oil light would both work.
 

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Thanks for the reply. I'm usually pretty good at basic electricity. Now the other end of the DK BLUE wire is in the engine compartment and of coarse it's hot with the ignition on. To ground this DK BLUE wire to make the light go on would cause a short in my mind? For some reason I can't wrap my head around it. I thought I had a crossed wire for sure .
Your reading the 12 volts on the blue wire through the filament of the bulb. The filament is resistance to prevent a short when the blue wire is grounded. When there is no current flow, the voltage is the same through a resistance (the filament).
 

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Your reading the 12 volts on the blue wire through the filament of the bulb. The filament is resistance to prevent a short when the blue wire is grounded. When there is no current flow, the voltage is the same through a resistance (the filament).
Don, It makes sense now. Thanks again, Frank
 

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Just put in a tee fitting so you can use both sending units. I did this when I had a mechanical oil pressure gauge so the gauge and oil light would both work.
Brian, I believe I had that T setup on another chevy years ago. Where would you look for the sender and the T fitting? summit racing I suppose?. Frank
 

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The T can be made up from hardware store pipe parts...I'd use black pipe....I believe its 1/4"...The sender is probably still available over the counter at the auto parts stores.
 

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Good to know...I will have to remember that for future use myself
 

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Brian, I believe I had that T setup on another chevy years ago. Where would you look for the sender and the T fitting? summit racing I suppose?. Frank
You should be able to get a t-fitting at any hardware store. I think it is 1/8" pipe thread but I would double check on that. You would need a nipple also to go in the block first and then the t-fitting. Try to find brass fittings as they will look nicer. The sending unit you should be able to get at any auto parts store or Summit. An auto parts store may have the brass pipe fittings too.
 

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Discussion Starter #17
Copy the file to a thumb drive, take it to KINKO’S and tell them what you want.
11” X 17” shouldn’t cost that much.
They have larger sizes but the process and the cost goes up.
Copy the file to a thumb drive, take it to KINKO’S and tell them what you want.
11” X 17” shouldn’t cost that much.
They have larger sizes but the process and the cost goes up.
That sounds like a great idea. I'm not familiar with thumb drives. What size thumb drive should I purchase?
 

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To do what you need to do here you will only need the smallest one they sell...Walmart has them for under $5
 
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