I've got an amp and sub lying around I want to try in place of my S3(8L) Bose sub so I've made an adaptor for the existing loom socket in the boot following Andy Mac's pin out. I thought I'd test the sound quality before running the power cable through the car by using a separate power source in the boot for the sub.
I've got one of these portable jump-start battery things and it runs the sub fine if I plug it into an audio source like an ipod. However when I connect it up to the wiring in the car it doesn't make a sound. Is there some technical reason that using a second battery won't work due to grounding or something? Does the remote-on pin need to be used from the car wiring??