problems with new to me mercury

first not getting air to remote tank to push oil to the engine tank on the oil injection system. Next tachometer is not working. eng is charging the battery at 14.6 volts. the tach moves a little but never goes up to 1000. I will check wiring under dash. previous owner had everything jury rigged and I think I have most of it rewired. horn wires were cut. injection tank on eng had a boat plug for a cap. blue and black wires spliced. got new cap and connected the blue and black wire. oil injection works if I fill tank on eng but it runs dry with a gallon in the remote tank.