I have two engines, two batteries and two battery switches. I took one battery out. In order for me to start the engines on one battery, I had to put one switch to No. 1, and the other to No. 2; otherwise, one of the engines would not have a connection. Anyway, one engine cranks over with no problem. The other engine does not want to turn over. I have to hold down the start button for about 10 seconds before it start turning over. Any ideas of what to check. Both starters are new.

I would start by looking at loose, rusted or corroded connections in the system to the motor and especially the ground.