This topic has been discussed in another thread but I'm putting it here for the records. I replaced the sending unit to the gauge but added a splitter so I can have an idiot lite too.
NAPA #s
gauge sending unit OP6640
idiot lite sending unit OP6619
Gates #s
3700x2
G60607-0202
Sorry, one is the splitter and one is the extention, but I don't know which is which.
Total cost $52.
The gauge works fine, but I don't have the lite wired yet, will report asap.

FWIW (followed the thread) Senders are on driver side, low on block, near front. Look like this:

So what are the 2 wires coming out of the lite sending unit? I know you have to have 2 wires for a connection, but the gauge sender only has 1 and it works, so I figure ground? I'm running new wire for the idiot lite, so what do I need? I know I'm asking a lot but I grab it when I can get it.

I think the pressure sender is a variable resistor internally grounded, ergo one wire.

I'm guessing without checking (I ain't going under there after dark!) that the other is just an isolated two wire switch. That way it can be wired into the hot side in series or as a switch to ground.

If you're wiring it all yourself and have the choice, run power to the light and run the ground through the switch. That way if the wire shorts somewhere to ground the light just comes on. Other way grounds out power lead and blows fuse.

(I just jumped out and checked the above on the wiring diagram in archives. Above is true for the 1 and 2 wire senders.)

FWIW: My replacement sender (NAPA)was hex-shaped, installed easily w/ 15/16" deep socket.
It's chassis grounded, so go easy with the Teflon or you'll lose ground - I've proved it

quote:

It's chassis grounded, so go easy with the Teflon or you'll lose ground - I've proved it

Never thought about that. I T-taped everything but it still works so I must have gotten metal to metal. My gauge sender was a can looking thing, kind of like an in-line fuel filter. The idiot lite sender is more like a spark plug.

OK one more stupid question. Lenny gave me a LED bar to use as an idiot lite. It has 2 wires. I put the splitter on the sending unit and have the idiot lite sending unit in place. So, one wire to an ignition switched hot source, the other to the sending unit? Doesn't seem right to me but I don't know what else to do. Also, if I wanted to use the same strip for a temp idiot lite is that possible, or do I have to have another lite strip for that?

Seems reasonable as the sensor in the block just completes the circuit by making the connection. You would want a different light for the water temp so you know what is causing the problem, but the same rule applies. The question I have is how the wiring is normally routed in a factory harness so you get the dash lights at start up? This allows verification that they are working. Someone here must know.

Corey, I don't have any factory idiot lites, just gauges. That's why I want to install this, so I'll know the instant I lose pressure, not after the damage is done. [That knocking noise is the idiot alarm ]

OK, one MORE stupid question. I just noticed one wire has a white stripe. Hot or ground or doesn't matter?

Project complete! I now have a working oil pressure gauge AND a working idiot light LED bar. A side benefit is I'll know if I accidently leave the key on. That bar is BRIGHT.

My dash has a "check gauges" light that indicates something is out of specs - temp, oil press, charging.