I'm posting this for a friend.
He just repowered his boat with some N/A 540's and is using a Tbolt ignition from a 330. Well the rev limiter is kicking in at 4500-4600rpm's. So they ordered new modules for a Bulldog thinking that they would be perfect for the application well the new modules will not work with his ignition. The harness plugs are different.
He really likes the features that the Tbolt has (knock sensor,timing retard,etc.) so he doesn't want to trash it for an MSD. But a 4500rpm rev limit doesn't cut it either.
Any suggestions ?

Which Thuderbolt ignition is he using? A thuderbolt IV (which is what I use) does not have a rev limiter. If he is using a Thunderbolt V or VI it does. Not sure if it is the same, but maybe he could use a module off a Thunderbolt IV?

I believe he is using a 5 series ignition.
Lenny our friend and mechanic doesn't seem to know the part number for the right module. He thought he had the right ones BUT when he opened the boxes they were for a different harness.

i swapped modules on my sbc from the Tbolt V to the 350 mag Tbolt IV. the module plug configurations are different so you ALSO have to buy the harness end which plugs into the module for the respective module (tbolt IV). takes about a half hour to swap the harness (mostly unwrapping that electrical tape) and a couple of cuts and splices.

i still wanted a rev limiter so i wired in an MSD soft touch...

Jaroot,
My friend Lenny (shopowner) is having no luck with Mercury. I guess since they are not Merc motors they won't give him any kind of help. I don't really know what he is doing now.