85 720 Charging System Issue

[hoffaa]

Hey, Folks -

I've got a 85 720 pick-up and have recently encountered a problem with the charging system. About a week ago, the battery light lit up on my dashboard. It starts out bright, but dims as the engine hits higher RPMs. I brought my battery in to a local automotive shop and had it charged and tested. Battery tested bad, so I put a new one in. Battery light still comes on when the truck starts and stays on while it's running. A new alternator was put on the vehicle about 3 months ago and the battery is brand new, so i'm not exactly sure why the alternator isn't charging the battery.

some things I've noticed since the problem started:
1) the interior dome light will only come on, now, when the engine is running - and when it's on, it's way brighter than I've ever seen it.
2) with the truck in Park, engine running and the headlights on, the dash will become brighter as I rev the engine.

i'm pretty sure I've ruled out parasitic draw with my multi-meter and the fusible links coming off the positive battery cable appear to be in OK condition. I'm somewhat of a novice when it comes to DIY auto repair and diagnosis, so i'd really appreciate any insight you could offer.

Thanks in advance.

[hoffaa]

Another pertinent point: I changed the t-stat a few days prior to this happening. As it was my first time doing this kind of thing (again - flying my "novice" flag), I took no steps to either clamp the hose or otherwise ensure that the alternator was covered. The alternator got a good dousing of coolant.

The internet has a lot of differing opinions as to whether or not a generous application of coolant will kill an alternator - but i'm wondering if that's not the case here.