Help! Lost tachometer, water t. gauge, alternator wont charg

[Saber]

I've got an AE86 with a AE101 4AGZE with removed a/c and power steering. It ran fine last summer, I drove it 2000+ kms (1240+ miles) and was stored in a garage through winter.

Now roughly two months ago I was going to put it back on plates and start driving it. In the first test drive, when I first floored the throttle, in the same instance, the tacho and water temp gauge died and the alternator charge light came on. A few kms/miles later it died because of no electric charge.

At first I just thought the alternator was dead (and thought that somehow affected the tacho and water temp gauge). But when I changed the alternator, the problem still persisted.

Then I thought it was bad grounding and checked that pretty much everywhere and the only place that didn't have proper grounding was the alternator body. Temporarily fixed that with some start cables, but the problem still persisted. (Is the alternator body/housing supposed to be grounded?)

(Yes the igniter has good grounding plus the head, block and transmission are grounded)

I tried finding a loose plug or burnt wiring, but since I did the wiring myself 2 years ago, I knew it should be solid and found nothing wrong with it.

What can possibly affect the tacho, water temp gauge and alternator charge at the same time? Anyone got any ideas? =(