oil pressure sender and elctro confusion

[bnoland@calpoly]

So when I got my '81 rwd sedan i noticed the connector to the oil warning light sending unit had been disconnected and wouldn't hold itself on, so i bought a new sending unit from the dealership. Then I realized the design takes a different type of connector, so I had to cut the wire and crimp one on. Now my oil warning light flashes when starting the car, when taking off from start, and at high rpm. It doesn't stay on, just gets brighter as rpms increase, either dims out or goes off completely. I'm pretty sure I can trust the bad pressure signal, and that the oil pump hasn't ever been replaced so I probably need to do that. BUT...I'm not sure if the sender is defective or my connection is bad. Do any of you know how these warning lights are supposed to behave, and whats going on here?

[freakinbox]

hmm... you sure you got the one you needed and not one that's for a gauge rather than a light?

[94_Rolla_Guy]

if in doubt buy a oil pressure gauge and check out the real deal

[bnoland@calpoly]

The sending unit I put in is what the dealership gave me, and I'm pretty sure its for a warning light since the car never came with a stock oil pressure gauge. But about that gauge...when I first used an aftermarket gauge, I got readings that were just barely in range, but still ok...and that was a while ago. But now when I use the same gauge, its reads pressure all the way up off the scale, and stays there regardless of rpm...its the electronic type where one wire goes to the sending unit, one to ground and one to "the fuse box where it will get 12 volts of power when the key is turned"....but I just connected it the positive battery terminal once I had the car running, figuring this is 12 volts just the same. Could I have broken the gauge? Thanks a lot for the help
...here's what the warning light sending unit looks like with the connection I made:

[toyomoho]

The pressure sender used with a light is an on/off switch. When the ignition key is turned on and the engine has no oil pressure, the negative wire of the oil pressure light is grounded through the closed switch. When the engine is running and the oil pressure is over say 5psi the switch opens, the wire is no longer grounded and the light goes off.

If the system uses a gauge, sender continuity (ohm resistance) will vary with the oil pressure. The sender is connected to one terminal of the gauge, dc power via ignition switch to the other terminal.

It is possible you have the wrong type of sender. Check resistance with an ohmmeter. For a light system, should be zero with engine off and infinity with engine on. The sender used with a gauge system will have its resistance (ohm reading) vary with oil pressure.

[freakinbox]

I am pretty sure thats the wrong sender. that looks a little large to be the on off style for the idiot light. It looks more like one I put on my car from an ae92 gts (4age oil pressure sender unit)

Don't trust the guys at the dealer, they have told me the wrong info before. such as starter repair kits not existing... But BAM they have one in stock when I find the part number! lol

[bnoland@calpoly]

absolutely right. i finally got a good multimeter so i could test the ohms, and the go down as the rpm and oil pressure increase- its a freaking gauge sender just like you guys said. Dealerships are officially hella hurt.

[freakinbox]

meh gauge is better than an idiot light anyways.

like I said, parts people don't always know cars, and the computers they use aren't always right. You have to know what you want and know enough about your car and models similar to tell them it's not right