My fiesta has 4 factory speakers but I want to leave the rears powered by the head unit and have the fronts (which will soon be Hertz 6.5" speakers) powered by an amp.

Now, I know you have to splice into the loom of the head unit, but how do I know which cables to splice? I have a Kenwood head unit and I know you have to splice into the head unit cables not the car factory cables, but how do I know which cables are for the front speakers?

Either your head unit manual will tell you, or you will have to trace the wires. All the 4 sets of wires for each speaker should be different colours, pull the front door cards off to find out which colours the fronts are and then look at the adapter you're most likely using to connect head unit to car and see which colour wires on the adapter the front speaker wires connect to.

I don't know why you are going to splice them though, on my last car I cut the front speaker wires on the adapter and twisted and taped the amp wires to them, as I presume you're doing this so you can use the existing wiring to the doors...

You would splice the wires if you are using the speaker wires from the head unit as an input to your amp because of a lack of RCA outputs on your headunit... Use RCA to input the signal to the amp where possible and don't splice the output from the amp into the head unit loom!

why not do a re-feed from the speakers them selves?

Either

your head unit manual will tell you, or you will have to trace the

wires. All the 4 sets of wires for each speaker should be different

colours, pull the front door cards off to find out which colours the

fronts are and then look at the adapter you're most likely using to

connect head unit to car and see which colour wires on the adapter the

front speaker wires connect to.

I don't know why you are going to

splice them though, on my last car I cut the front speaker wires on the

adapter and twisted and taped the amp wires to them, as I presume you're

doing this so you can use the existing wiring to the doors...

You

would splice the wires if you are using the speaker wires from the head

unit as an input to your amp because of a lack of RCA outputs on your

headunit... Use RCA to input the signal to the amp where possible and

don't splice the output from the amp into the head unit loom!

Ok when I said splice all I meant was cut the head unit speaker wires and tape the amps speaker wires instead :)

I dont have a manual for my head unit, i'll have a look for one online.

why not do a re-feed from the speakers them selves?

There's no way I have the patience or time to do that, and its not even necessary when I can just wiring into the factory cables.

To connect the Kenwood to the Fiesta you will need something like this wiring adapter;

http://www.nexxia.co.uk/products.asp?category=Ford+ISO+Radio+Harness+Adaptors&Make=Ford&Model=Fiesta&Reg=f%29_Sep-05_-_Dec-08&Additional_Details=414&Submit=Detailed+Search

Then cut into the gray_gray/black and white_white/black wires for the front speakers.

Details here;

http://www.fiestaguides.co.uk/content/ford_to_iso_mk4.html

Thank you, I have run speaker wire from the amp to the back of the head unit and have cut the wires you mentioned, however I have a slight problem.

The speaker wire I have is gray, for some reason positive and negative arent marked at all so I have no way of knowing which is which. If I wire them the wrong way will any problems occur and if not is it easy to tell if they are wiring right or wrong?

If you connect them wrong then you will loose bass from the front speakers. In which case you could change + and - at the amp end on one speaker only.

If you connect them wrong then you will loose bass from the front speakers. In which case you could change + and - at the amp end on one speaker only.

Ok so at least no damage will be done, but why only correct one speaker?

It doesnt really matter which way round the positive and negatives are connected up, so long as both speakers are connected the same way, if one is pos to pos and neg to neg and the other speaker is pos to neg the sound waves from each speaker cancel each other out rather than working together to create a stereo sound, and this gives the impression of a lack of bass. So you change the wiring of one speaker to put it back in sync with the other and stop the waves cancelling each other out.