I confused.
I was going to fit my new alt last night. I unplugged the wires ready to remove, but realised it was going to be a slightly longer job than planned, so decided against it.
Anyway, I forgot to plug the double wire pigtail back on, so the alt is effectively running as a 1-wire. When the engine is running I am now getting a charge, but way too high. At idle 16-17volts and when running 2-2.5rpm, it's off the scale 19-20+??
What's going on. Is it safe to run with these high voltages (until I get the new alt on - so only short term)