Car electrics - screwed?

Default screwed it!!
right um, i think i've screwed my cars electrics i've been having problems with my stereo for a while now,last night i jumped into my car with a veiw to fixing it, it came to my attention that the original wiring loom, the AC cable is knackered, (the red one)i figured this out by joing the cable on the wiring loom to the cigarette lighter cable, and hey presto we have power, so i try it back on the other cable, it dies.

so i get a cable from the cigarette one, join the two together, take one to the stereo, and the other to the lighter, its works fine, well not really, as soon as i turn the key to the accessories posistion - i hear this whirring noise coming from my dask controls - speedo rev counter etc, but it goes off nearly straight away, and engine turns on fine, i get up to go to work, and realise my trip switch has reset, as my time, and does so everytime i turn the engine off

a few things i can think of

- a fuse has blown on the old wiring loom -

Answers:
Depending on the make and model of your vehicle, there are also a few more scenarios..

You could have fried the CPU on the car, you could have fried a relay (or two, or three), you may have a wire shorting out somewhere touching metal (grounding out).
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