Find ANY switched circuit with a fuse LARGER than 5 amps and add your own 3-5 amp fuse to protect the Racepak.
One of these will work depending upon where you want to tap in.
Fuse panel Add-A-Circuit:
https://www.amazon.com/dp/B0146EB8EM/
Inline fuse holder:
https://www.amazon.com/dp/B018W2T7XS/
This post has more info about installing the Add-A-Circuit (12 pictures down):
http://www.ft86club.com/forums/showthread.php?t=16300