I'll start from the beginning so not to miss something I've done, so some of this info may be irrelevant. 05 Cayenne Turbo

Fitted towbar and electrics, and now warnings all over dash for PCM and Air suspension. So...

1. Lifted car to terrain height, took off rear bumper, rear lights and left car overnight.
2. must have left something on, battery dead. Put on charger in engine bay points and only reading 5v, would not charge as result.
3. Removed battery from under seat, tried again and reading 12.5 volts, took charge ok, so installed back
4. Started car, and now
a) air suspension fault (changed gaskets 6 months ago) - although car going up and down fine - it was left up overnight though, with a flat battery.
b) PSM fault. Car will not clear PSM fault as per owners manual, and PSM on/off light on dash not working.
c) Clock resets itself after I start the car back to whatever time it was last set ie, manually set clock to 10.05 am, it will then work while running or sitting until car is restarted later when it will jump back from current time to 10.05 am?
5. looked for auxiliary battery under BOSE sub in boot - i don't have one!
6. Bought a new battery anyway, changed it over and still no difference.
Nearest Porsche 2 hours away!
Any one got any ideas?

 

Disconnect the battery. Disable the towing electronics, and return to stock. Hook up the battery. Drive a good 10 miles in all conditions. If the problem goes away it was your install. ?