nvu

Odd, it should not kick off from charging at all for these models. There's no ecu control if it's 2 wire so no way to tell it to power off. Do you think there's a corroded wire in the harness causing intermittent charging? If you have a spare connector, dash lightbulb, and a switch, you could make a dongle from the alternator to the battery + and manually force the alternator on to test.

It should work. Only models I know need all 3 pins on the alternator were the sti and XT models with the 32bit ecu, electronic throttle. If yours is cable throttle, it's the old style and only uses 2 of the 3 pins.

I went reverse, 2006 alternator in 98 impreza. Swapped from black rectangle to green oval plugs and works fine. Though 13.5-14v at the battery is kinda of standard nowadays, it's okay for newer batteries.

If there's air, theres a leak. Check the lines for wetness and under the clutch reservoir. Get a scredriver and depress the slave piston in so you can wiggle the clutch fork back and forth. It should only move in two directions. If it's flopping all over the place, somethings broken, bearing, fork, pivot pin.

Other places to check. If near the rear passenger, check the pcv hoses. If turbo, theres a middle block nipple that likes to leak when the clamps weaken from heat.

I don't know for sure but suspect eyesight equipped vehicles need this step. I heard it's a nightmare to replace windshield glass with an eyesight system and it needs some special alignment and setup again. Not something any windshield shop can do.

I vaguely remember a youtube video about having to hook a computer up to the car and set something before installing the brakes. I'll see if I can find it again...

Try steering with the fill cap off and see if tiny bubbles apear. If so, likely the S shaped hose from the reservoir to the pump has gone brittle and sucking in air at the pump nipple.

There's a module you unplug to turn off the DRL permanently. On an 02 impreza it's passenger side glovebox/footwell area near the fuel pump relay. It's probably the same area on your legacy. Download the service manual for your car and find out.

as a test you can just skip it all together and short the connector pins together. the compressor should kick on. its function is pretty basic, too high or too low pressure it'll switch off. it'll short the pins when the pressure is nominal.

it's likely fine, the timing chain tensioner can get sticky, but doesn't fail catastrophically like the timing belt tensioners. those years had the oil consumption issues due to low tension rings from the factory. probably check if your model year is affected and keep an eye on oil levels between changes

oil filter up top is an fb engine, timing chain. they're noisy on startup until the tensioner fills with oil. no need to replace if it doesnt sound bad when warmed up

Check if the cabin heater working. If so the pump is working. Might still be some air trapped in it, try parking at the steepest incline you can and do the radiator fill again.

I only see one wire tapped from the main harness. can you trace blue/pink wire and see if it runs into the ignition switch? guessing it's a breathalyzer module that needs breathing into to start the car.

The suspension gains positive camber really quickly when it's near the end of its travel. Not sure what's causing your too high issue, but the vibrations are likely from the tires gaining positive camber when the suspension bounces up higher than usual.