Originally Posted by
rideevol
Do your initial measurement at the battery. 12.7 volts is desirable for a fully charged battery with engine off.
Engine idling should increase voltage above 12.7 volts which indicates charging, still at the battery posts. Now you have a baseline. Any measurements at gauges, choke heater wires, alternator output wire etc. will now add to your understanding of wire and connection condition. RPM does have some effect even on an alternator so voltage up to 14 is also normal for healthy charging, especially after an engine start-up.
This is good advise, id start here. for what its worth, my relic 88 sunsport idles at 600rpms, alternator puts of 13.7v at that rpm. my gauge shows 14v at idle. earlier this year my gauge was stuck on 12 just like yours, alll the time. my charge wire from the alternator to the battery was bad, i had to run a new wire.
Check output at the back of the alternator while running, and check the batterys also. if you have over 12.5 at the alternator, but less at the batteries, check the charging wire from the back of the alternator to your batteries. If they are both above 12.5, then id suspect a faulty gauge or a voltage drop somewhere in the instrument cluster. This shouldnt matter if its a digital or anolog gauge, The voltage running through the wires should be the same
1988 Supra Sun Sport 454 PCM
1972 Olds Cutlass 455
1998 BMW 750il
1996 BMW M3 coupe
1995 Toyota Tacoma 4x4