1990 Corolla -- third wire on alternator harness?

[until it rusts]

Can't find connection for extra alternator wire.

I just replaced by alternator after seeing charge and brake lights coming on intermittently. When removing the old one, I found that in addition to the two large wires that were connected, there was a third, small, black wire routed around the alternator and below it. I never felt anything pull out, but when I had the old alternator out, this third wire was loose, with a small tab-type socket on the end, like the type that might go to a sensor.

I looked everywhere but couldn't find where to plug this thing back in. Finally I installed the new alternator, made the two main wire connections, and drove off, leaving the small wire unplugged. So far I have driven 50 miles in two trips, highway and city, and not seen anything unusual. My charge/battery light comes on as normal when I start, and goes away immediately.

Anyone know what this wire is or where it is supposed to go? Could it be there unused as part of some option that I don't have?

[foodaa]

Do you have A/C? I think the wire you're talking about is for the A/C compressor.

[toyotaspeed90]

is the wire yellow with a black line? it sounds like your oil pressure switch wire

[until it rusts]

Yes, inside the jacket the wire is yellow with a black line. Two questions:

Where should I look for the mating connector?

If this is the oil pressure switch, what are the consequences of driving with it off? Does this operate the indicator on the dashboard? The weather is nasty and I don't want to mess with it right now if I don't have to.

Thanks.

[toyotaspeed90]

all that wire does is send a signal to the dummy light in the car. if the oil pressure drops, the light comes on. it's not connected to your ecu