I have a 90 amp 1 wire alt on it's way for the R5.

My questions are, What size wire should I run? Where should it run to?

I have a switch on the rear tail panel, but I always hear about problems with the engine still running after shutting off the switch. I'm thinking the wire should go straight to the battery right? So this will take a heavy wire?

I run one wire from the alt to a solenoid in the trunk that is between the battery and the alt and a second wire from the alt to relay box under the hood that is used to power the headlights and fan.

In my situation if I wanted to kill the alt from a switch in the tail panel I'd need a second solenoid.

Both wires are #6

i used #4 to be safe.how do you have your car wired for power for shutting it off from the driver seat?

I have a switch on the dash to shut the IGN off..

The simplest thing to do is run a long large wire < size depends on lenght and amps> to the batt B+ or the batt side of the cut off switch, I am assuming your batt is in the back, the larger the wire and the better the quality will determine voltage drop from the alt, care full wire routing and chafe gear is important , fusing the output wire is up to you depending on how safe you think the run is and the wire used, proper crimp ends and shrink tube is a good idea, I always run agw wire one size larger than the chart recommends and never had low voltage problems, this is the basic simple stupid way to do this, there are many other ways to wire this system just look up the posts

here is one way

other

one more ..All are just food for thought

And here is how I wiil do mine kill switch

cable go up front