Thanks all the for suggestions and info! I am swamped with family life, and this happens to be yet another Volvo that needs attention, so I apologize for the delay in the turn around. I finally got around to firing up and tinkering with the 944, so I figure an update is in order.
After sitting for half a year, the alternator now no longer kicks on: even at red line. This alternator was recently rebuilt and has a new voltage regulator, so like you guys I am more suspicious of the wiring and control circuitry.
I confirmed that there are no dashboard warning lights lit at the key on engine off state. I am appalled that neither of the two previous owners nor their mechanics mentioned this when asking me for advise on the fuel gauge. I pulled the cluster and was impressed to find three obviously cracked solder joints which further confirmed that the cluster was not even checked. After resoldering and reassembly, the fuel gauge is operational. I suspect it no longer matches the fuel sender unit because the needle said 3/4 for what should be a full tank.
While the cluster was out of the car, I checked the charge and a few other warning light bulbs, and none were burnt out.
Unfortunately, the resoldering has neither enabled the warning lights nor the charging circuitry. I am now planning to cross-reference those two circuits and double check the connections and look for tampering. Sadly, this car has some custom cut and spliced wiring, but I hope it is limited to aftermarket audio equipment.
Yes, the alternator has 3 wires attached. However, I completely forgot to check if the exciter wire is getting signal. This alternator also has an "internal" exciter wire that can be attached instead of the car's, and is currently detached. I have tried swapping to the internal signal, but found no difference in the car's running voltage.