Received my new M&H under dash harness

I have an aftermarket radio and tachometer and 3 little gauges (amps, oil & temp) I need to add to the system. ....but I don't wanna butcher my new harness. ...

Gonna need some tips on adding stuff without being a bubba....

I'm all ears guys!
on my Duster, on the inside firewall I added another block of connectors (it has female spade connectors in it) that I tied into the fuse block. It has a few of each of full-time power and keyed power, so when I want to hook something up I just connect it there.