car battery kept draining . Mechanic disconnected navigation device & cd player. Now radio goes off every 45 seconds or so.

Hi guys brand new here need some helpful advice looking
to buy my first bimmer tomrrow got into a car accident a
few weeks ago and insurance is taking forever to settle so
in the mean time I'm lookin at a 528i its a 99 with 133k
miles talked him down to 1,500 he said the car runs great
only problem is all the windows don't work I've replaced
window regulators before that's not a problem I got him
down really cheap cuz of it but there's also this 740il with
160k miles he wants 1,900 but he's willing to negotiate
has m5 front bumper looks great and he said drives like
new I could really use some insight help here what do you
guys think I should do any feedback would be greatly
appriciate I'm so exited to own a bmw!!

I replaced the stock radio system and put a aftermarket system in. Used some of the wire to power the radio, but others are taped off to the side. But after a few days, lights started messing up. When I turned the ignition over, the low beams came on and all the brake lights illuminated and stayed on. I have no turn signals, no hazards, no high beams, no fog lights, and no rear license plate light. The computer where the speedometer and gauges are don't work either.

I even changed the fuel line and the wire harness with the one the engine came with now it won't start at all

I'm hoping that it is a problem with the automatic settings for each driver. Problem is that the door switch is broken. Disconnect it to fix problem???

took car in for water leak they didnt have tools to repair. picked car up and it started smoking. runs fine no noise and i parked it two days and checked oil and water. it is smoking much less now what is up.

lost. Advised to get drive cycle of car to figure out how many miles need to be driven in order for test to work. How do I find this out? Is this true?

Right now I am in Las Vegas it's very hot, transmission won't shift RPM is at 3000 MPH 25 won't shift out.
After the car cools down it runs perfect. A mechanic told me it was the transmission temperature control regulator. The part is a $100 and to install it is $100 would the transmission do that if it was the regulator...?

The time change was recently replaced. U shaped rail was broken. Light stays on engine light. error code 342?????