I just purchased a project 86 SE V6. It was not running. Got it running with a new coil and distributor rebuild, but determined it needed a water pump which is installed. Now the idle is all erratic and the volt idol-light is flashing on and off systematically every 3 seconds. (Volts is fluctuating between 10 and 11 volts, sometimes less.) Previously before the water pump was installed it had no such issue. Whats going on? Any ideas? Wiggling alternator connector reveals no connection issue.

Belt tension is first thing that comes to mind. Belt slippage on the alternator leads to lack of output.

-- A

All grounds are in place?

Just above the water pump is the MAP sensor and a lot of vacuum lines. Check to see if any were damaged during the water pump repair.

[This message has been edited by Gall757 (edited 05-31-2020).]

quote Originally posted by dremu: Belt tension is first thing that comes to mind. Belt slippage on the alternator leads to lack of output. -- A

It was the belt! bingo.