Could simply read http://www.fiero.nl/forum/Forum2/HTML/138175.html
for most of this...
Because the picture was shot "wrong," the left C2 plug hole doesn't line up easy w/ some traces to follow them.
The other ignition on C3 is for alt bulb to turn on the alt plus alt warning if alt has problems.
Plug connects both by jumper there to design board easier.
Ignition on C2 is power for gauges and some bulbs.
2 blank bulb holes are "Spares bulbs" and should have sockets at minimum to block light leaking.
Fiero Designers had something planed for those but canceled for whatever reason. 1 N/U pin is ground to one when on. GM cut contacts to the other light to repurposed to run OP gauge.
(Even 84 has both listed as Spares bulbs but have board contacts for them going nowhere after the plug.)
Temp/fuel Gauge Clips are power, ground and "signal" for top, reverse order for bottom.
Tach clips OP, Power, Tach on top, ground at bottom. This dash must be for GT because never had OP clip. (I think 84 Dash "board" and back plastic are different and can't take OP clip.)
(84 use same warning bulb for Temp and OP)
Note that those clips are just 1 reason the dash gauges lie to you. Oxide "Rust" makes problems both on the "board" and on gauge "bolts" to plug into the clips.
Gauges have resistors bolted to back of them gets crap or loose nuts cause same problem.
Oddly the 84 docs have Illumination lights shown for temp/fuel gauges but ignore them for later years and why the other page I had to add O & P bulbs.
------------------Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)The Ogre's Fiero Cave
[This message has been edited by theogre (edited 05-23-2020).]