[Uhehner]

Yep, I agree, that's why I did not attempt to answer his question. 

Steve, there should be a DC schematic in your owners manual or you can have one e-mailed from Tiara.  I would expect the gauge reading to drop when you put a heavy load on the battery while starting.  Both engines should be the same. Do you keep the battery selector switch in the BOTH position?  I never do. When in the BOTH position, if you have one dead / bad battery you will now have two dead batteries. I only use the BOTH position for starting if one battery won't do it. Most Tiaras have a parallel switch.

More information concerning the BOTH position: If you always keep the switch in the BOTH position so that your electronics do not drop off line when starting I have a fix for that using  two diodes and a spring loaded switch or a battery combiner ( not a battery isolator ). I install it on all my fishing friends boats and it works great. Contact me for the schematic diagram.

Capt.  George