im using this harness.. it turns on.. sound comes through but alot of feedback.. anyone using this one with the same problem? and the sub isnt working...

 

Those harnesses work well but if you have a cheaper head unit they seem to always be noisy. Either backround noise or engine whine. To get the sub to work you need to wire a RCA end on the correct wires. You could try a inline noise filter which will kill some of the level going to the factory amp. May clear up the problem your having with the noise.
Otherwise its amp bypass time.

 

tuterz:What kind of harness is that? Metra?

dentpusher: Newb question here, I'm trying to install a Panasonic Nav. What do you mean "wire the RCA end".

 

You wire in a male rca end to the sub signal wire. This will allow you to hook you rca sub out from the radio to the dedicated sub input to the factory amp. This will allow you to keep the factory sub and have control over the level.

That harness doesnt look like a Metra one. Metra uses different colors on the rca ends and they are shorter too unless they have changed it.