anyone got pic of back of gauges/circuit boards for '68 barracuda/?

The 2 large wires bolted onto the amp gauge are both firecracker hot at all times. You can do more harm than good trying to fix anything from underneath. If you do have a loose contact pin at a connector you'll surely have more than the one.
Free download factory service manuals detail how to remove the inst' panel for services. The headlight switch and wiper switch can be replaced without removing the inst' panel.
The pic provided above shows a aftermarket inst' voltage regulator added on. The OEM mechanical voltage limiter is inside this 3 post fuel gauge. This is the number 1 most common fault.
Pull the inst' panel. Repair and test everything at the workbench. Reinstall when plug and play ready. A solid state regulator, a dedicated ground wire, etc.., will make it better than original.
I don't stop short of 8 new bulbs and sockets. I replace wiper pivot seals while accessible and lube speedometer drive cable also. Everything I can do while in there.
I did work hard before I learned to work smart. Smart costs a lot more but... not only is this inst' panel more difficult to R&R than a standard panel but it is quite fragile and booby trapped in a couple of places too. There's a spot where circuit board is larger than the housing its on. Improper handling got me (can't find my pic). Anyway...
You don't want to R&R it repeatedly for one fault after another. My most recent mistake was cheap Ebay bulb sockets. Of course the first to fail was a turn indicator. Pretty much impossible to replace from underneath. Live and learn.
Everyone has their way of doing things. Service manual will state nothing about removing the seat. It isn't necessary.