I have a Toyota MR2. I installed keyless entry by soldering into the power lock/unlock wires and the constant 12V wire. All good. I then tried installing LED lights by using T taps on door trigger wire and the same 12V. I blew one fuse multiple times doing so, causing me to lose power to various electronics including the instrument gauges. I gave up on the idea.
Around this time, the battery light started flickering. Then it got worse. I would lose power while driving, dash lights would flash (mainly battery, P/S, ABS), no power steering, can't use lights, gauges dying etc.
Replaced alternator, belt and battery.
Issue persists but in an odd way. Car will be fine but if I brake "too much", it will resurface. Or sometimes when I push in the clutch. After driving for a bit, the issue will correct itself. Repeat.
I am guessing I shorted something somewhere? But then problem should be constant. I am stumped.