Hoping SOMEONE has seen this. One 1990 7.4 engine I've determined has a short somewhere. Not sure how or why, but one is not affected and the other is. I thought it was fuel related so I emptied the tank, replaced the fuel pickup, the fuel pump fuel line, water separator and fuel filter. Still having issues. Sometimes if both engines are running it's ok, but alone 80 percent there is issues. So while the engine was running I discovered if I shut the battery switch off it ran nice and smooth off the new alternator. Turn the battery switch on won't rev over 1000rpm and just choughs and chokes. Shut battery off again and it runs smooth. Sounds like a short somewhere??? Any ideas???

hello,,,wow...did figure this out??
wierd u shut off battery switch and runs good??
sounds electrical....bad ground?? guessing here...

Tell us exactly how many battery switches and batteries are being used / wired. A drawing would be great.

Hello all, yes very confusing to me. Drawing may not needed? I just have the one battery switch for the whole boat, and only 2 batteries. So battery 1 on position 1 and battery 2 on position 2. On the out put side of the battery switch is each motor starter and the house. Everything is all tied to that one output on the one switch. I'm hearing that maybe this shouldn't be all tied together? And it sounds like tying it together has created a problem somewhere, because it runs smooth once started if I shut the battery switch off.
Now it seems like my damn Thunderbolt 4 module is dead, WTF. I have 12v on the purple wire at the coil but nothing on the white/red coming out of the ignition module. Maybe this F'd up wiring caused issues with that also??
I just bought this 1990 Carver Allegra twin 454's with Bravo 2's last year, drove it home (about 160 miles) with no issue until I got to my port then all this started. Any suggestions with wiring and/or ignition module would be greatly appreciated.

You’ll have to check for proper wiring and power/ground to the ign module

As far as batteries and switches, few ways to skin the cat, but here is 1 of them:
https://www.perko.com/help_guides-wi...attery_switch/

You won’t have the cut out switch, that is for Alpha drives.

Do you have an electric choke? Is it closing for some reason?

It is not an electric choke, I did find that I do not have any power coming out of Thunderbolt 4 ignition module, but have the required 12v go in.
Thank you

Also ck grounds to ign module/amplifier and also the one to the distributor. Very important they are hooked up and in good condition !

See wiring diagram above.

Thank you for all your help. It turned out being the sensor in the distributer. This engine had the older style with the exposed components and 2 studs for the ignition module to attach to. The newer style (which is what my other engine has) is complete sealed with flying leads. Replaced that unit and it fires up better than ever.
During the winter months I'll rearrange the battery system, it only makes sense to separate things like you pointed out. Summers too short here to keep working on the damn boat, lol.