We have a 89 camaro 350 tpi. We while on startup the guage shows a healthy 14.5 volts. As warmimg up it'll go down to 13-12-11-12-14-13-12-13-11-13-12 its alllll over the place. But this is only when its warmed up. It was recording 12V at highway speeds. No matter the rpm. I have a new Yellow top Optima (did it with old battery) Direct 4guage wire from top of batt to the back of alt. Red wire to a 16G FL by the starter and the tan wire goes into the loom lol. (BTW did this with another harness we had in the car as well) We took car to autozone and hooked it up while running and they said the volts were showing what the guage was showing correctly. They said it was only putting out about 25 amps. They said it should be putting out alot more. They said in order to really get a good test I have to remove it and bring it in for another machine to test it. Before I do that (its a PITA with the SC) i wanted others options. Thanks!