Does the thunderbolt IV have a rev limiter built in? I've seen an old post on another site that said that, but never any mention of it anywhere else.

No

Yes apparently some do. I have 97 525sc s that I spent last week chasing down a no spark issue, turns out it was the overspeed assembly aka rev limiter. I am told they rarely go bad. Mine was located behind the triangular shaped module mounting bracket. All ignition wires go into it, and it will keep your engine from starting. It can be bypassed with an older short wiring harness. Fyi the replacement part is $608 and change. The are some sparse references to it, but I could not find any mention of it either. It may not exist on all Thunderbolt IV engines.

The rev limiter for the TB IV only comes on Merc Racing/Blue engines and is an add on component. Its not built into the module. Stock TB IV's on Merc/Black engines don't have a rev limiter.

It's item # 43 in this picture
http://www.mercruiserparts.com/Show_...2%2DF213244%29

Good to know, I've got one of the BIII 'Performance Tuned' 7.4s - came with forged internals like the 454 mag. So, this tells me I won't have to worry about the ignition in my planning for a few more HP and rpm.

I have a TB1V with overspeed rev limiter on 525SC and had the connector turn green on lower terminals at the amplifier. I purchased a new V8 22A amp and it came with a cable without the overspeed box. I put it in and bypassed the box and all is well except no overspeed.

Now I have another green connector on one of the other engines.

Does the overspeed circuit reduce the 12 volts going to the coil? I have less than 11 volts even though the purple wire is 12.
Does anyone know the color code for the amplifier plug and the connections to the coil and distributor. I will cut the cable from the overspeed box and connect the amp to the coil and distributor directly.

Apparently the cables are obsolete..

I had both rev limiters go bad in 1 week I just cut and spliced the harnesses to eliminate the rev limiters

Was the Failed limiter symptom unable to start when warm?
Did the wires to the limiter use the same colors as the wires from the limiter?

same question as snapcrackle.....
i have a fial rev limiter adn want to bypass, jsut need to confirm which color wires to splice
tks
Ramb