Issues when changing head units 1991 735i

I just recently took out the stock head unit and replaced it with a sony xplod i believe. Instead of purchasing a wire harness i decided to do it myself and cut/crimp the wires together. Only issue is, i did not realize that the stock units harness had 2 cables of the same color being blue for the negative polarity of the right hand side speakers. On the left hand side speakers the negative polarity cables are grey and there are 2 of those.

Basically i made the mistake of cutting these 4 wires without identifying them and i was wondering if there was any way of telling which is which (front or rear). I have already connected all the other wires up and have the unit powered playing a CD trying to test the speakers. All of the positive wires are hooked up and i just need to identify the negative ones so i started connecting the 2 left side wires to the wires on the sony. Still none of the speakers work. Is there anything that i might be missing? i have double checked everything and nothing has worked.

Any insight is much appreciated,

Donny

One way to do it is get a continuity tester to each speaker terminal and connect one end to the one in the dash. I believe on the speaker there's imdented marks which tells you which on is possitive and which one is negative. You'll probably need a friend or your wife/girlfriend to hold the one end in the dash. While you have the speaker out, you can also identify which speaker wire is which.

Unless they changed it in '91, my 1990 750 the speaker wires are all subtly different from positive to negative. The only similarity is that on the 8-speaker system, two speakers in each corner run off the same color wire.

On the 10-speaker system, the speakers should be running of an amp which is located in the trunk/boot of the car on the left hand side (looking into the trunk/boot from the rear) behind the panelling, in which case, the wires connecting the speakers to the dash may or may not be the same and you may not get continuity as the amp is turned off.

see i have all the positive wires hooked up for the speakers and i have all the power wires connected to the head unit, but when i go to hook up the speaker negative wires no sound comes out.. what do i do?

You must have the 10-speaker system then, which means you have the amp in the trunk/boot.

Here's what you do: cap the negative leads and make sure they don't ground out and leave them unconnected. Lots of guys have done this without any harm. The amp only needs the signal, the speaker grounds are connected to the amp, not the headunit, and the amp already has a ground, so you don't have to worry about the negative speaker leads off the headunit.

So if i cap the negative leads, (what would be best), then the speakers should work?

see i have all the positive wires hooked up for the speakers and i have all the power wires connected to the head unit, but when i go to hook up the speaker negative wires no sound comes out.. what do i do?
I read this wrong initially. I thought you said you hooked up the positive and there was sound.

Do you have the 10- or 8-speaker system? There should be a speaker in the dash on each side, a speaker in the kick panel (where you feet go) in the front and two speakers on each side on the rear deck shelf. For the 10-speaker system there are two speakers on the door by the mirror on the inside.

If you have the 10-speaker system, try turning on the headunit without the negatives hooked up and see if sound is produced.

i have a 8 speaker system, i've already tryed not hooking up the negatives and just leaving them covered. me and a friend are going to try and by pass the amp tomorrow. ill let you know what the out come is

Unless the amp has been retrofitted, there is no amp on the 8-speaker system from factory as far as I'm aware.

The only thing left to do, is get a continuity tester and test the end in the dash to the end on the speaker and figure out which wire is which. You may be surprised that you've hooked the wires up to the wrong ones.







It's been a few day since your last post, and I've been a way for a few days, has everything worked out?

i just went a rewired every speaker to the new sony xplode head unit and just installed 4 new 5.25 memphis speakers.. sounds great!!

im thinking about getting a amp for them.. but later on down the road, i want to do some more work to the car, like air intake, rims!!, the halo headlights, and just do work.