I am curious for those who are using a fuel pressure and oil pressure guage, did you drill a hole in the firewall somewhere. How do you get the wires from the bay upfront to the guage? Is there a correct way?

I just ran mine alone the wiring harness. Wasn't too hard.

I don't know how correct it was, but I took mine up the center tunnel from the engine compartment. If I remember correctly, there is a rubber grommet or plug I took them through, then up the tunnel and into the back of the gauges. You may want to try Phonenix's method because I found my way a PITA.

If you're crafty, you can get them shoved through the stock wiring conduits.

If memory serves, and mine often does not - check for unused wires under dash and in engine compartment. Wiring for A/C or some unused option.

My first -6 had one or two. Seems like green & black. I used one for oil pressure gauge in ashtray opening.