ok I am relocating my battery to the trunk. I have my 15 feet of 1 guage pos cable going to a remote solenoid on the firewall. the question is for my bat terminal wire comming off the alternator, can I run that to the same stud on the remote solenoid as the pos cable going to the battery or do I need to run a sep wire to the back of the car for the bat terminal wire to mount on the pos post on the battery???

 

By now you have likely finished your battery wiring... but there's no need for a second wire from the alternator to the rear of the car. Your plan to connect the alternator output to the feed side of the solenoid is good.