Just started up my 66 today with a 289 after my T5 swap. Everything mechanically is working fine, but i do have an issue with the charging system. The alternator was rebuilt about a year ago but the car sat since then. The car starts fine and at idle im only reading about 12.2 volts, and will slowly drop off to about 10.2 and hold....WTF? I replaced the voltage regulator but still no change, im at a loss for words...Everything looks to be wired fine, and i do believe the alternator is putting SOMETHING out, because if i turn on the headlights, the voltage will drop as it should (to about 9.8 volts from the 10.2) and when they switch off the voltage comes back up to 10.2 volts. Thanks for any help. I just wanna drive this thing already!!!!


Mike

 

I feel your pain and I'm in the same boat. When running disconnect your neg cable if it dies the your alt is not putting out.

 

^yup^

 

Your alternator should be putting out a regulated 14.5 V or higher@ about 2000 RPM. rev you car to 2000 and what is your voltage output? SB 14.5 -15.2 - if it is you have too much electrical load for your system to keep up with at idle (you need a bigger alternator and wiring improvements)
To simply test your charging system:
if less than 14.5 remove the electrical plug from the regulator and momentarily short the White and Yellow wires the voltage should go way up above 15V ) this is called "full fielding" and is the test the auto parts store does with their machine.

If it goes up the V reg is bad or you have a wiring issue between the Alt and Vreg.

If it doesn't go up, check the wiring between the ALT and V reg plug, if its good, the alt is bad.

 

Thanks for all if the input and help guys! After a little research I found that the place that rebuilt my alternator has not been doing a good job with rebuilds as of late. I am going to take the alternator to get bench tested today and see if its putting out the correct amperage which I believe should be around 60-65 amps. I have all stock electrical features so I doubt I will need more than that. If this doesn't work I guess it's on to the troubleshooting stage, which you guys have given me a step by step for. Thanks so much!

Mike