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Trying to follow what you're doing. Are you putting a switch on the constant power pole of the relay and using a dash switched function to activate the switch in the relay?
 

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I'm just not understanding why you would want the relay closed when the car is off? Wouldn't you only want it closed when the car is on so the battery bank will charge? Otherwise you want it open so your main battery isn't drained.
 

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No I meant not drain the main car battery. The secondary battery cell will always be connected to the rest of the system downstream from it. You just want the relay to tie everything to your main battery/alternator when the car is on. You want ignition on signal to close relay. And use mobo or switch to trigger amps and such
 

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Two small relays. One triggered by the acc position in the car, and the other with a switch to trigger the second relay. Both relays wired to remote turn on, main 12v and ground. One relay will only be closed when the car is on which will be primary form of remote turn on. Second relay you only use with no key. Just shut off switched relay when not in use.
 

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Thanks. I considered two relays but would rather only have one if backfeed is not an issue.
If you use ignition on power to close the relay and use battery power on the supply side, you can just use a switched battery wire to energize the system. Ignition + > relay close +, ground > relay close -, battery + > relay supply side in, relay supply side out > audio system; battery + > switch, switch > audio system. No backfeed because the supply side of the relay is battery + as is the switch.
 

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Two small relays. It's not overly complicated. You could maybe do one relay but you'd want a diode to block power from feeding back to the acc switched trigger. I think two relays is the better solution. You'd only use the second relay with a switch in no key mode.
 

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Car computers (ecu/bui/ect) are freaking expensive to replace. If you can avoid backfeeding current/voltage and possibly damaging these expensive computers why risk anything? 2 relays at less than $10 is worth it for peace of mind to me.
 

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I'm not an automotive expert at all. I am a little confused to your aversion to using two relays? You're already going to have a switch for no key operation. Why not put a relay in the two circuits to minimize any possibility of backfeeding current /voltage
 
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