I have an 1975 belgian mercury 500 (50hp), manual start, thunderbolt ignition which i want to equip with a tachometer. Faria tachs are available in Croatia, and i wonder how to make the connections to the motor. The tach has signal pole, battery positive and a ground, as well as the light connector. Since i don't have electicity producing on board, i will recharge the 12V battery from time to time, and will the tacho working draw too much juice from the battery?