This pic shows a modified oil tap at the block on a B21FTi. It was done so as to hook up a mechanical oil pressure gauge and keep the idiot light.

The sender on top of the Tee is a regular B21F pressure sender [with 1/8 NPT threads]. That is connected to the black wire that goes to the low oil pressure idiot light in the dash.

The nylon tubing connected to the bottom of the Tee fitting is plumbed to the 0-100 PSI mechanical oil pressure gauge in the auxilliary gauge panel in the dash.

This arrangement was done in order to clear a higher output alternator. It cleared the back of the alternator, but it was close. Shortly thereafter, the alternator was moved over to the other side of the motor. The old alternator bracket was left in place.