Im having a problem with the charging system, its not charging the battery. I ran a new wire from alt post to battery and it was charging 14odd volts at idle, but now its not again, when I drive the battery light come on then off, on off ect...

Whats the best way to test the alt? Is it at the screw post at idle? I'll do this once the AC charger has charged the battery

Way i did mine, pos lead of multimeter on alt post, neg lead to neg terminal on battery.

and what about the other 2 wires on the alt, I ran the positive on directly to the battery and it started to charge, but now it wont

do basic checks to like battery terminals and terminals on alt. if they have high resistance it will cause problems.
check what how many amps are coming out of it to.