Mercruiser Thunderbolt IV no power to coil

[alltypesofstuff]

Hey guys, I've searched the threads and found a few posts that were close to my problem but not exactly thus the new thread. Any help would be greatly appreciated.

88 V6 4.3 with thunderbolt IV ignition (Module on the exhaust)

My boat died on the water last week due to no oil, I found an oil leak at the oil filter.

Now I can't get any spark. I'm not getting any power to the + side of the coil even with the gray tach wire removed from the - side. This is with the key on.

Are one of the wires going to the ignition module supposed to have power because non of mine do. I first replaced the coil but if there is no power going to it then it would have to be something else anyway correct?

thanks again

 

[Don S]

Re: Mercruiser Thunderbolt IV no power to coil

No power to the + side of the coil is a problem is either bad ignition switch, faulty kill switch (or lanyard came off), or a bad wiring connection from the ignition switch to the coil.

 

[alltypesofstuff]

Re: Mercruiser Thunderbolt IV no power to coil

I found a blown fuse right after the ignition switch and replaced that just now hoping that was going to be it and still no power to the coil. I checked the new fuse thinking that there was a short somewhere and maybe it blew right away, not the case. Can I jump from the switch to the coil or from the battery to the coil?

 

[Don S]

Re: Mercruiser Thunderbolt IV no power to coil

There shouldn't be a fuse in the purple wire, it should be in the red/purple striped wire going to the ignition switch battery terminal.

You can hot wire the ignition, jumper from the battery positive terminal to the + terminal of the coil.

The starter is cranking the engine over isn't it?

 

[alltypesofstuff]

Re: Mercruiser Thunderbolt IV no power to coil

The starter is cranking the engine, yes.

The ignition switch is the key switch right? There is the constant hot, then the wire that splits to all the accessories when in the on position (this is where I found the purple fused wire) and then the one that only gets power when starting, for the starter.

I'll put a jumper from the battery + to coil + and see what that does.

Should I disconnect the other wire going to the + coil while doing this? Leaving the + and - from the module and adding my jumper cable?

 

[Don S]

Re: Mercruiser Thunderbolt IV no power to coil

Yes the ignition switch is the key switch. You can hot wire it, but it's not going to tell you where the problem is. You are testing at the coil with your black test lead of your meter on a good clean ground aren't you. It DOES NOT go to the negative terminal of the coil.

here is the wiring diagram of how your wiring at the helm should be.

 

[alltypesofstuff]

Re: Mercruiser Thunderbolt IV no power to coil

Yes, I was testing straight from the negative battery side.

Wiring from the + battery straight to the coil did the trick. It's running now!

So the wire that goes to the + side of the coil is just an accessory wire right? I can run a new wire from there to my ignition? it's 12V, nothing fancy?

 

[Don S]

Re: Mercruiser Thunderbolt IV no power to coil

So the wire that goes to the + side of the coil is just an accessory wire right?

Fix it right, don't just do a half fast bandaid fix.

 

[alltypesofstuff]

Re: Mercruiser Thunderbolt IV no power to coil

I plan on fixing it right I think. I'm planning to run a wire from the ignition to the coil. But it normally runs through the main wiring harness so I'm wondering if it is responsible for anything else or does it just go to the coil. If so then a new wire straight from the ignition to the coil would be the correct fix, right?

 

[Bt Doctur]

Re: Mercruiser Thunderbolt IV no power to coil

like Don says, you need to FIND THE PROBLEM first.Then make the proper repairs.
have you checked the main harness plug at the engine. bit loose, loose/no clamp, slight corrosion will kill 12v too.

 

[alltypesofstuff]

Re: Mercruiser Thunderbolt IV no power to coil

I did check the main harness and it has a clamp on it. I took it off and it's surprisingly clean actually.

Didn't I find the problem already? I assume the wire just fried somewhere, it is 25 years old. So running a new wire is not the correct and proper fix?

Either way, I'll trace the line when I run a new one and thank you for all of your help. love the site.