what is my secondary battery suppose to read while car is running

[Jasonc13 33]

At least you're in Hawaii, not the NE states this year  I would still rather have the power runs in the cabin if you can make it work.  Drilling a hole in the firewall and inserting a gromet is not hard at all.  Toughest part is getting the correct drill bit.

[Jay-C76 333]

Just be careful where you choose to drill.

If you drill into a wire harness or something else on the opposite side of the fire wall you'll

be in a world of pain with even bigger repairs.

[Frostedflakejake 148]

If you drill into a wire harness or something else on the opposite side of the fire wall you'll

be in a world of pain with even bigger repairs. 

 

One good reason to use a greenlee punch. It can also sometimes be difficult to get a drill along with a bit to physically fit in a location to allow drilling.