Ed,
Let me add a bit more detail to Eric’s inputs.
Fuel Gauge: Pg 20 of the 2004 Monterey wiring diagrams in Coach Assist shows the fuel gauge circuit. Since your gauge is reading full all the time, you have an open circuit between the tank float mechanism and the gauge (or a faulty gauge). Low resistance drives the gauge to full and high resistance (~90 ohms I think) drives it to empty. The wire from the float assy goes thru 2 connectors to get to the gauge. Looks like you’ve got a bad connection (i.e. poor crimp) at one of the connector pins (unlikely), a broken wire (relatively unlikely) or a bad connection at the gauge or a faulty gauge. I’d check at the gauge. If you run 12V thru a variable resistor you should be able to drive a change the gauge reading. That would confirm the gauge is working. Then you’ll need to locate the open wire or run a new wire to the gauge, unless the float mechanism is faulty, which can be checked with a meter.
Cruise Control: The cruise control circuit is not shown in the 04 Monterey diagrams we have. Eric is correct that TB1-7 in the front electrical bay is the brake signal that deactivates the cruise control if the brakes (service or exhaust) is applied. (See pg 21 in the 2004 Monterey dwgs). Since your brake lights work, I suspect this circuit is working. The 2004 dwgs don’t show the cruise control circuitry but the 03, 05 and 06 Monterey diagrams do and should be very similar to the 04. All show a cruise control deactivate relay that captures both the brake and smart wheel cancel signals. It’s relay 4 (R4 or K4) in the front electrical bay.
Steve