The system that provides voltage to the D+/61 terminal on the alternator has the dash warning lights (not the oil light) in series with the alternator rotor windings.

In other words, from the + battery, voltage flows to the dash warning lights, through the red wire (gray connector) and to the D+/61 terminal. That terminal connects to one of the brushes, so the circuit goes through the rotor windings to the other brush, which is grounded.

The voltage between D+/61 and ground should be quite low, like 2 volts or so, since it is reduced by the warning lights.

When the alternator begine charging, the ground is lost, and the lights go out.

The oil pressure sensor is a ground when the pressure is below a certain psi. thus when the engine is not running, it is a ground. Connecting the red wire there provides a ground until the oil pressure rises. What you found was normal, and may indeed prove tht the wire is OK.

You say: At the B+ terminal of the alt, I'm getting nothing grounding on the frame and about .10V grounding at the Btry. terminal.

That B+ is the charging circuit. The wire is a large gauge, connects to the starter lug where the main wire connects from the battery. The B+ is therefore "hot" all the time, key in or not. If you tested between B+ and ground, and got nothing, something is not right there. You should get full battery voltage.

Testing between ground and the battery hot side should give the same results as between ground and the B+ alternator terminal. If not, your problem lies in that connection.

You may have to open up the under-the-engine harness to see what's going on with that fat red wire.

Good Luck,

Bob

:>)