Should you have a ground wire between each block so both motors are grounded to each other, or can I just ground both batterys to each other???

I always run a ground cable between the engines but I can't think of any reason why grounding the batteries together would not be OK.

ground motors together. if 1 ground goes bad, will still let you crank using other engine as ground wire.

fountain runs both battery grounds to a common ground terminal mounted near the center of the transom,and one ground wire from the terminal to each engine.on my cat,i ground both battery,s togeather,it,s been working for the 3 years i have owned it,so id say either way will do the job.

Exactly! If 1 ground does fail, then the starting circuit will try to use the next closest grounding path w/o that 2ndary cable.... your fuel line!

The block to block ground wire is a safety feature, not a convenient feature

that makes sense,looks like il add a ground wire from 1 engine 2 another tomorrow!

Looks like I'll be adding some ground wire also