Thunderbolt IV wiring question

[Fishermark]

I'm helping my brother with his new project. He has a mid eighties vintage Mercruiser Chevy V-8 (305 I believe) with an alpha 1 outdrive.

The engine was shot, so he rebuilt it. It originally had a points ignition, and I have a Thunderbolt IV distributor that I salvaged from another engine a few years ago. I have never used the Thunderbolt IV, and I am not sure if I have the correct wiring diagram handy, so I have a few questions....

From the picture below, here are my questions:

1. The black wire going to the distributor cap hold down screw - is that simply a ground wire?

2. There is a white wire with a red stripe on the left terminal of the distributor body, and a white wire with a green stripe on the right terminal. They are both loosely attached, so I don't know if they are supposed to go there or not. Are they correct?

3. From the module, there is a 2-wire harness with what appears to be a purple and grey wire. Does that go to the shift interrupt switch? If so, is that a typical shift interrupt that simply goes to ground?

4. The short black wire from the module - does that simply go to ground?

Any help would be appreciated! And even a link to the appropriate manual or wiring diagram. Thanks in advance.

 

[John_S]

Re: Thunderbolt IV wiring question

From SM #17, T4 Alpha Module on exhaust elbow:

Purple: Coil +
Gray: Coil -

The blacks are ground

The wht/red and wht/grn go from dist to module
The wht/grn also goes from dist terminal to gray at shift interupt

You need a T4/5 coil

T4 doesn't use a resistive wire.

 

[Bondo]

Re: Thunderbolt IV wiring question

Ayuh,.. I think manual #9 covers the T-Bolt IV,....

If I remember right, ya the blacks are ground, the grey is the tach, 'n the purple is the ignition...
Not sure if the order matters on the distributer...

 

[Don S]

Re: Thunderbolt IV wiring question

1. The black wire going to the distributor cap hold down screw - is that simply a ground wire?

That is not OEM, doesn't belong there.

4. The short black wire from the module - does that simply go to ground?

Yes.

This wiring diagram should answer the rest.

 

[Fishermark]

Re: Thunderbolt IV wiring question

Perfect! Thanks for the help everyone.

 

[Fishermark]

Re: Thunderbolt IV wiring question

That is not OEM, doesn't belong there.

Don - looking at the diagram a little closer, it does appear that there is a ground wire coming from both the module AND the distributor. It isn't very clear where is attaches specifically.... but could that not be the wire that is currently attached to the cap hold down screw?

 

[Don S]

Re: Thunderbolt IV wiring question

No, there isn't any ground wire from the distributor to ground, the housing is the ground, that is done by clamping down the distributor not with a wire. The amplifier itself is grounded, and on yours is usually on one of the mounting bolts for the amplifier itself where it mounts to the elbow.

 

[Bondo]

Re: Thunderbolt IV wiring question

Don - looking at the diagram a little closer, it does appear that there is a ground wire coming from both the module AND the distributor. It isn't very clear where is attaches specifically.... but could that not be the wire that is currently attached to the cap hold down screw?

Ayuh,... Factory or not, I've run across distributers that had a little screw in the bottom, pointed up, with a ground wire on it...

 

[FreeBeeTony]

Re: Thunderbolt IV wiring question

Ayuh,... Factory or not, I've run across distributers that had a little screw in the bottom, pointed up, with a ground wire on it...

I know mine has it...........doesn't seems to make much sense............but I left well enough alone...........

 

[Leedanger]

Re: Thunderbolt IV wiring question

Ayuh,... Factory or not, I've run across distributers that had a little screw in the bottom, pointed up, with a ground wire on it...

I found this is manual #18....I didn't find the same info in manual #9 although it does indeed cover the IV. Here's a link to manual #18 https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B1TAvwZ3TjhfYWRiMDZmNDctMzgzZi00MmIzLTkxNGItMGY1NGExYjJmOGJh&hl=en_GB

Here's #9 : https://docs.google.com/leaf?id=0B1TAvwZ3TjhfNzllZTk0MDEtYWUwNC00NWFmLWFhNzAtZTU2NzNhNjAwMWM2&hl=en_GB

View attachment 118965

 

[achris]

Re: Thunderbolt IV wiring question

Ayuh,... Factory or not, I've run across distributers that had a little screw in the bottom, pointed up, with a ground wire on it...

Hey, that was my doing.

Back in 1995 I had a problem with my new 4.3LX, losing rev when the engine was warm. Cool the engine would rev to 4900, warm I would barely get 4000. After the dealer and Mercury had given up and told me to 'live with it' (sound familiar?) I decided that there was something wrong and I would find it... Took me a while (about 4 months on and off) I found that as the engine warmed up, the iron (block and manifold) and aluminium (dissy body) expanded at different rates and it lead to a resistive ground connection (I know you're all going to tell me that's not possible... I found out that it is!). That changed the advance curve and I was losing about 8 degrees of advance, hence the loss of revs. I found an unused ground wire in the engine harness and hooked it to the dissy body. Problem solved. I fed that back to Mercury and about 9 months later all the new Thunderbolt IVs were coming though with the dissy grounded.....

Chris.........

 

[Fishermark]

Re: Thunderbolt IV wiring question

Thanks for the info everyone - Chris, how you even thought to look at that is beyond me!

 

[achris]

Re: Thunderbolt IV wiring question

Thanks for the info everyone - Chris, how you even thought to look at that is beyond me!

It was all that was left after everything else checked out ok..... :facepalm: