If the the older "CS" type alternator was used, they use a 194 peanut but in the dash for current limiting. If not use used, a 460 ohm resistor will limit current, not voltage for turn-on signal. A peanut bulb when lit, will have a 460 ohm resistance across it.
Aftermarket voltage regulators for AD244 have different requirements, but produce 13.2 for hot operation and 14.3 for cold as these systems including the CS series are temperature sensitive. Remember, its the current and not so much voltage that counts as they alternator supplies current to all of the trucks goodies, while trickle charging a known good battery while driving with less than 1.0 amp.
If it is all factory, you will have to go with the factory service manual in the wiring diagram for 97. I think in 99, the AD244 is run using the PCM with a "Duty Cycle" circuit. The OEM voltage regulators for CS and AD244 has over 30 part numbers. That's why they don't sell them at the dealership.
For those who have the factory wiring for the 1999 you have, is the best way to make it work correctly. Alternatorman.com has a lot of information on these and other series of GM alternators as well.
Best of luck as very little "Plug-N-Play is out there when making changes with aftermarket parts. What does the "Instrument Cluster" people say?
If you paid up to $600 or so for it...I think they owe you and answer.