Funny Electrical problem
I recently purchased a Manta 40 (catamaran). It has two Volvo Penta MD2030 engines. If one engine is started, the tachometer for that engine runs properly (either engine). When both engines are running, the port engine tachometer stops. The previous owner reported that the problem started when the alternaters were upgraded to 120 amp alternaters. Any thoughts or suggestions as to what is causing the problem and how to correct it would be greatly appreciated.