Re: Weird grounding block bolted to firewall
I had a similar spaghetti wiring issue on my 68'. I'd follow one red wire back and it would be spliced 5 different times, in all different colored wires, till it came to the correct wire color at the firewall. Awful what a hacked up wiring job can do. From there, it's a matter of following it to the fuse to see what the heck it's supposed to be for.
Take one wire at a time and follow it back to the fuse box or other origin. It helps to have the correct year / car wiring diagram to figure out where these wires are supposed to go. Once the basic wiring is done (lights, charging, etc.), move onto the aftermarket wiring. You may be able to find wiring diagrams for the aftermarket gauges at the manufacturer's website.
The kid next door challenged me to a water fight. Just waiting for the water to boil...