new alternator- still have battery light and brake light - runs great wont shift well

So a few weeks ago while driving my battery light and brake light came on. A few minutes later my van slowed to a crawl and could not start again. My battery and alternator were no longer working well enough, so I replaced them. Put my battery in backwards, blew the 80amp fuse behind passenger seat and the EFI fuse in fusebox. Switched those out. My radio died during this process... and still wont work...

Now I have a new alternator, new battery, new power steering pump, new transmission filter and fluid, and it starts up and idles great.
Unfortunately, I still have my battery light on, my brake light on, and it drives terribly. No power, goes into gear slowly and with a lot of hesitation, too crappy to drive out of the driveway.

I checked the codes, they read normal. I checked the alternator voltage, reads pretty normal (13.8 at the battery terminals at idle).
Any help would be hugely appreciated. Feels like a transmission problem but reads like an electrical problem.

is the ground cable good?

Ground is good.
Pulled my RPM relay and it had a blown transistor.
Also pulled my ECU and it also has a blown transistor.
ECU blown transistor accounts for the battery light. Probably a host of other issues as well.
Strangely, there is a broken diode in my ECU that appears to be unrelated to this event. Maybe it has been broken for 31 years?

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Hi everyone.
My 84 Van is runs and drives seemingly well however I have some mysterious electrical issues.

The primary issue is my brake warning light and charge warning light will not turn off.

I also have no horn, no hazards, and no illumination (a pain when trying to drive at night). My headlights and taillights work fine.
Everything seems in fine shape otherwise.

I have a new ECU, new EFI relay, new battery, new alternator (charging fine), and my fuses and fusable links seem fine.

I'v got the 84 manual and I'v been doing my best to investigate using the wiring diagrams at the back, however I'm not entirely sure I understand how it all works/how these symptoms might be related.

Any help would be greatly appreciated.

Thanks everyone!

Let's start out with the basic/simple stuff. The brake light comes on when the e-brake is on or when the brake fluid reservoir is low. Make sure the e-brake is all the way off and fill the reservoir up to the full line. As for the dash lights, there's a little knob down low, just right of the steering column. This adjusts the intensity of your dash lights. All the way CW is bright and all the way CCW is off. Make sure it's not off. Tim

Thanks Tim,
Parking brake is fully disengaged and brake fluid level is looking good. I can pull the parking brake up, and sometimes the brake warning light gets even brighter. As for the dash illumination, I'v cranked that illumination dimmer all the way up and still get no light. Is the a way to bypass the rheostat to see if that is causing problems?
I can't help but think the brake light and charge light are related because they came on at the same moment when my alternator died.