Hey guys I need some help. Im helping a friend install a 1988 Merc. 420HP with TRS transmisions in his boat. The problem we are having is that there seems to be an excessive amount of sending units. For example..There are two on the transmision,two that look like hobb switches on the oil filter remote housing and three down on the block oil filter adapter. Now I know one of the senders is the oil pressure and one is oil temp,they are pretty easy. But what the heck are all those hobb switches for and how do we wire them? Does anyone have a wiring diagram they can post for us? We are in a rush to make a run in a week and we are stuck in the mud right now....

Thanks Anthony

if the boat has been equiped with a warning horn sys. that could be what some of the switches are, is there an electric fuel pump? could have a shut off for that? and one could be for a hobbs meter, is this engine from another boat?

Engine is the original for the boat. He just pulled to have rebuilt and didnt label the wires to the hobb switches. Its just weird cause one on the filter housing has a red wire from the hot side of the coil to one terminal and then runs down to the hobb switch on the trans.The other terminals are grounds.Why would they short the coil out with the oil pressure hobb?And no electric pump,they were and still are block mounted mechanical.

TTT.Someone has to have an idea??

I have a diagram for the older TRS , 330/370 but It only shows oil sender and oil press. switch(for alarm). Only reason for the wire coming from hot side of coil would be for a fuel pump switch, but even that should be breaking the ground side of pump. One on trans would be for alarm the other is neutral start switch (not always used) but usually there.Three on block are prob. press, temp, alarm. the ones on remote are probably the same and remote was added on after. I would get rid of the wire to coil because it shouldnt be there.