My Dads favourite shaver, Philisave HQ980 needs a new head plate. Its an old model but my dad swears by it & refuses to use his new one.

Remove the door panel and use your voltmeter to see if it's getting power and ground. If it is, then you need a new regulator.
Replace window regulator Ricks Free Auto Repair Advice

If the transmission was slipping, there is no fix for that

Being a 1992 i would talk him into parting with it

To old to be rebuilding a trans & you will need wiring
diagrams & most likely more knowledge than you have
to use them, for all the electrical issues

Hi amp draw from pump or bad relay--could be both as failing pump stresses relay.

on my 97 grand marquis there was a sticker on the trunk hinge with the code to unlock the door

my dad knows how so ask him my dads name is Rick

you dont say if its standard fitted model hifi unit, i take it you have pulled the din plug out of changer unit and checked all the pins are there? push plug fully in, check head unit end too, if thats done i had one that needed resetting on head unit, another the disc unit had dodgy earth lead, they dont norm give up. saying that my dads gave up when he hit a spped hump to fast. tricky...

This happend to my dads truck and it was the timing chain. Yours might be a timimg belt my dads was a 2000 chey sonoma

could be the manifold

You need to attach the blue wire on the stereo harness to the blue and white wire on the car adapter harness. they installed a small amplifier to power the rear door speakers and unless you connect those two wires then the speakers will not work.