MooneyCFII

Yes, circuit breakers can go bad in that they will eventually trip at currents less than rated. That should NOT be the case with the gauge-cluster since its normal current draw is well under 5A. So even a breaker that is old and has reduced capacity should not begin to nuisance-trip with just the gauge-cluster as a load. A key point here in your trouble shooting is that you said that the breaker would trip almost immediately. If you mean that you let it trip and then immediately reset it and it tripped again immediately, that is actually normal behavior for a good breaker. These are thermal circuit breakers and unless you let them cool down after tripping, they will trip off again almost immediately. OTOH, if you let the breaker cool down and then it tripped again almost immediately you are probably looking for a short-circuit somewhere. Examine the wiring bundle under the panel for wires that have chaffed against any of the metal structure. As for changing the breaker, the entire breaker assembly on the right side of the cockpit may be removed from the panel as a unit. You need to remove the glare shield and then disconnect the large Amphenol connectors that bring all the wiring to the breaker module. You will also need to unbolt the heavy cables that come from battery and alternator. Once you have the breaker module removed from the panel, changing the breaker itself will be a piece of cake. Oh, and of course you planned to disconnect the battery prior to working on the breaker module, right?

The final arbiter of CHTs is, of course, the manufacturer's recommendations. The values you find in the POH supersede everything. If something is not specified in the POH then refer to the engine manufacturer's manual for your engine. If you don't have a copy of the Lycoming or Continental manual for your engine, you should get one. There is useful information there that Mooney didn't put into the POH. Even though red-line is 460F for the TSIO-360-LB1 in my '231', Continental recommends 380F-420F maximum for cruise. I know that Lycoming recommends keeping CHTs in the vicinity of 370F and not over 400F for greatest longevity. So, taking these two pieces of information together, I strive to maintain CHTs in the 340F-380F range for all flight regimes. In climb for me this means that the cowl flaps must be fully open. In cruise I run with the cowl flaps in trail which usually results in 320F-360F. Closing the cowl flaps causes CHTs to rise above 400F on two cylinders so I don't feel I can operate with cowl flaps closed in cruise unless I operate at reduced power. (I normally cruise at 65% power running 25F lean-of-peak for a fuel-flow of 10GPH.) During descent with the cowl flaps closed my CHTs run around 280F-300F. As for what is the minimum CHT, the green arc for CHT on my airplane is 250F-460F. That means you do not want to run with CHTs lower than 250F in flight. I think I saw someone suggest that lower is better and 175F was just fine. Based on the data in my POH, I would recommend against that. This is how I have been operating aircraft for 45 years. I have successfully taken several engines beyond TBO operating in this manner. (I have only been doing lean-of-peak operation for the last 15 years and have only taken two engines to TBO using LoP operation.)

Not having to reduce power after T/O is usually true for normally-aspirated Lycoming engines but some normally-aspirated Continental engines have a maximum continuous MAP and RPM that is lower than takeoff MAP and RPM. (Take off power is limited to 5min typically in these cases.) The upper end of the green arc on the MAP and tach are a clue to this.