Speed is typically a mechanical gauge, not electrical. See this link -
Our pick up sensors are built into the outdrive but all the same theory’s apply.
Fuel is typically a ground issue, lift the cover and look for any broken or disconnected wires, you should be able to see the tank down low...
Tach could be a few things… no signal from distributor is where I would start.
Once you get into it a little let us know wire colors and locations of things that don’t look right, then we can move forward.