so it is either the alt or vr?
is the vr part of the computer that year?

can you check for voltages to the field wires on the alt?

if it is part of the computer, the older style vr are pretty stand alone and you can bypass the original pretty quick. use the 1 field vr electronic type. most places only carry the electronic type. is easier to rewire to me, and doesn't require a special plug.