Not enough power for remote amps

so I was working on a dual amp setup with a 1 farad cap. The plan was oem dash with a 4 channel amp going to the doors and a 2 channel amp bridged going to a small 10" sealed truck sub box.

I have the amp remote wires hooked up to lighted switches and in my workshop (wired to a spare battery) the switches lit up like champs, the amps powered right up and pumped signal to speaker cones for a time (until the battery was discharged). Wiring the setup into my '03 ep3 the remote switches barely flicker and the amps won't even power up.

my possible diagnoses are: i have an tired alternator (original 2003 stock), i have a tired battery, my gauge of wire to the amps in the hatchback is too small.

any insights would be appreciated, project has lingered for far too long.. this equipment belongs in my car, not in my workshop collecting dust.