Doug, the only component I can find common to those instruments is the 20 way Caerbont instrument module connector (not all pins are used). On the chassis loom side of this connector the relevant wires are green/black - fuel gauge and a green/blue - engine temp signal with latter coming from engine loom on white/green wire which shares signal with ECU.
Thankfully the PCB doesn't seem involved and no relays either. Might be worth breaking then making the connector plus the usual check on associated chassis/ground connections if the fault(s) reappear.
