Alt light comes on 1 minute after starting a cold engine. When the engine warms up to operating temp the light goes out and it charges. The speedometer jumps around while alt light is on then settles down rock solid when the light goes out. One cold morning I heated up the alternator (heat gun) and the alt light did not come on at all, it charged normally from cold start.

 

Is this just a bad alternator (it's new) or could there be something besides the alternator causing this.,?

any odd sounds when the light is on?

it does seem like you've found the problem but, I think I'd want to check at the battery with a voltmeter, check the belt and maybe check the crank pulley for slippage. (it's 2 piece and can delaminate)

Alternator is junk. Get one from Subaru. The reman alts for those cars are like $80 from Subaru. 

GD

35 minutes ago, cap86 said:

 alternator (it's new) 

aftermarket alternators, starters, and fuel pumps are typically trash, i avoid them at all costs. so it's the opposite what you'd think - "new" probably means that is your problem. 

Subaru reman is $70 or so from the dealer. Go get one and return low grade aftermarket.

Has the exiter wire (12 v switched) been replaced or messed with recently? 

A screwy exiter will cause wonky readings at the battery.

But yea as stated above, your alternator is suspect.

Thanks, all.

No odd noises at all, I adjusted the belt to no avail. Jiggling/wiggling the alt wires has no effect and one morning I unplugged the wires and heated that plug separately - didn't make any difference. I think it's time to get a Subaru replacement alt.