Bad relay base??
 

I am helping a friend with a 2005 35’ Fountain with Merc 575’s. The port side fuel pump isn’t getting voltage so the first thing I do is pull the relay off of the base (located on a bracket at the back of the motor). The base has voltage for the relay coil and for the pump feed as well. I switched relays with the working starboard motor and the problem stays with the port side so that excludes the relay. The wiring from the base to the fuel pump checks out with my Fluke meter. When I place a jumper wire on the relay base the fuel pump starts and runs. The only thing that I can determine is that somehow the relay base is bad. There is no corrosion and the sockets look great. I am wondering if the coil voltage is cut somehow by the ECU or something. Any input or suggestions are welcome as I am stumped. The owner says the boat ran perfectly last time out.

The PCM supplies GROUND to the relay coil. Power is full time. No PCM signal to ground the relay, no relay operation.

The ECU grounds the coil -
Check continuity from the relay base to the ECU
Check all connectors - even a small amount of looseness or corrosion could kill the ground
Check the voltage on the wire from the relay base to the ECU (with a known good relay installed) - it should be no more than a volt or two when cranking.

Thanks for the replies guys. I did check the ground for the fuel pump, but not the relay coil other than reading voltage on the sockets that feed the coil (reads 12.9 volts). All voltage readings were done with the key turned on, but not cranking. Doing so on the good motor gets the fuel pump on and primed.