Replacing a 28 year old Thunderbolt IV ignition sensor assembly that was 2-wire + a 3rd ground wire that was connected between the bottom of the sensor mounting screw and the TB iv module bracket mounting bolt (@ the exhaust manifold)...The module’s ground wire was also connected to the same bolt.

The instructions for the new ignition sensor says to ground the new 3rd wire at the main flywheel ground point which is not doable without fork lifting the engine cover off. IS THE BRACKET MOUNTING POINT ON THE EXHAUST MANIFOLD AN APPROPRIATE GROUND SPOT?

anywhere on the block for the 3rd wire be fine. I’d imagine their just looking for another ground source via corrosion etc. Just a guess.

how can you not reach the main ground point with the engine installed? Where is the battery cable ground connected? I doubt your ignition module bracket is bolted to the exhaust manifold. Electronics and heat don’t get along well.

I “personally” can’t reach the main ground point...minimal space and I’m old...the bracket mounts to the riser/manifold joint of the emi thunder exhaust. I’ll find another spot and maybe connect the module’s ground wire to it, too. Thanks for the input.

I understand a bit better now. It should be fine there. Your first description made me think you had a bracket coming off the bolts that go into the head. Any secure clean spot that is metal on metal to the block should be fine for that ground.

i have the same cobalt hull the engine hatch is also the rear bench seat making it hard to access the back of engine i pull the hatch pin and block the hatch straight up i also switched it to the delco est dist it runs and idles better...the est,s idle with a lot of inital timing making a big block smooth

...yep I lift the heavy SOB and prop it straight up...I suppose it would be easier if I also removed the 2 bulkheads/walls that wreck my laying down room. I feel for boat mechanics, for sure. Thanks for the help.