No wiring diagrams per Miller Yachts, the importer. The oil and temp are sensitive and balanced for upper and lower helm. The upper and lower must be connected and working for the others to work. The senders are specific for one or two gauges.
Please connect all grounds please.
The engine hour meter runs because it is powered. It does not need the engine running to count hours. There must be something wrong with the key switch. It needs to be wired to cut power to the lower tach when turned to off.
34' Marine Trader