Compatability question: '77 911 with '78 3.0 - possible '77 ext. VR & '78 int. VR

[pkfrdh]

I swapped out the orig. basket case '77 2.7 for a '78 3.0 years ago. The car and motor are both still low mileage (under 70K). I only did the mandatory swap out of the '78 Bosch CD unit and re-ran the external wire for the '77 breaker style points into the body side engine plug to mate to the correct pin in the '78 engine plug. I changed nothing else...still have the '78 oil pressure sender.

I never considered if there was a '77 orig. external voltage regulator (VR) that would conflict with a possible internal VR on the 3.0 alternator.

The car has been driven lightly and infrequently over the years and I am now noticing that there is only 12 volts coming to the battery. I haven't gone through the 101 Guide's check list to diagnose the charging system yet such as when and how bright or how long the alternator light comes on or off when key is on w/ car running or not.

Does anyone know if there is any immediate problem I should have addressed with regards to the VR compatibility? I looked under the '77 body fuse cover on the rear inner fender panel (left side engine compartment) and see a square black plastic unit that is mounted just rear of the '78 Bosch CD unit and the raised printing on it says: "Marschal S.E.C. 14v". My guess (?) is that this is the original '77 external VR. I have no idea if the original '78 3.0 came w/ an alternator that has an internal VR.

Any input on the potential swap problems (immediately voltage regulator issues or less immediately any other notorious issues) would be appreciated as I go through and do the charging diagnosis.

Thanks,

Joe L. in Santa Barbara, CA