Port Fuel pump only runs with Starboard Ignition switches off?

[Tyler Vanden Bergh]

I have a 2004 SeaRay 290 Amberjack with Mercruiser 5.0 MPI engines. I can get both engines to run but for some reason my port fuel pump won't run when the Starboard ignition is in the on position. I have to turn off the Starboard ignition switches and then the port fuel pump will run and let me start the port engine. I can then start the Starboard engine. Any info on things to check is greatly appreciated!

 

[Highliner]

It might be a long shot but pull your fuel pump relays and examine the contacts closely. They have been known to have a bad connection and melt inside the relay bases. Could be that your port connections are marginal and any extra drain in the batteries is enough to cause issues. Once you have an alternator spinning the problem would potentially be masked.

 

[capecodcruiser]

Check your grounds connected to the engines around the bell housing. I had an issue last year similar. Randomly found a green ground wire with it separated from the ring connector. Bad/disconnected grounds can cause all kinds of issues.