Mercruiser Coil Wiring

[Lloyd R]

I was boating and my 1996 Crownline 7.4 Mercruiser stalled. I tried starting and noticed spark at the top of the coil. I was coming out the side of the tower. It looks like the previous owner put an automotive coil on.

So, not being a electical mechanic, I began trying to figure out what electrical system I have. Thunderbolt IV or V. I'm still not 100% sure.

Also, I noticed their is a resistor block and some splicing of a wire that goes to the block (yellow wire) and the other (red wire) to the starter.

Since this seems very dangerous as it is, I would like to return it to factory wiring set up.

Any suggestion?

 

[Scott Danforth]

If it's a resistor block, the thunderbolt ignition has been changed

Post a picture of the distributor without the cap

A ballast resistor is common with the Mallory/Sierra YLM distributors, along with a few orhers

 

[Lloyd R]

Thanks for taking an interest in helping me out!
This is with out the cap.

 

[Lloyd R]

Here is the back side of the distributor.

 

[alldodge]

You have a TBV ignition and the prior owner is a dumb A$$

Remove the resistor mounted on the boat

Get the correct coil, inspect your wires as they may need replacing, than go boating

 

[Lloyd R]

Ohh man your awesome. I agree with your assessment of the previous owner. You should have seen the nightmare starter situation I had to fix last year.

I want to fix the wiring. In pic #3 labeled "Spliced Wires", the "red" wire with a butt connector has a splice with 2 leads. Red to the starter and yellow to resistor that I'm doing away with.

On the coil I had 2 grey to - terminal. On the + I will have one purple and one Blue (goes to oil pressure switch).

Is that all good?

 

[alldodge]

Do some really good tracing because from here things are not correct.

My pic for a standard TBV has 2 gray on the Neg, and one purple on the Pos. The Yel and Blue should not be there.

Having a Blue on the Pos side of the coil would lead me to believe a different oil pressure switch has been installed for some reason

I'll ask, does this motor have a mechanical fuel pump or electrical?

Next
What is the serial number of the motor? It should be found on the flame arrestor or on a plate just above the starter

 

[Lloyd R]

Wow, this makes me pause. I really want to get it back to original.
I will have to get that serial number. Hopefully tomorrow afternoon.
Thanks for your help

 

[Comogene]

As stated, the TBV system used a non-resister coil and does not use a ballast resister or a resister wire. I'll bet the previous owner used the wrong coil and added the ballast resister. Get the correct coil and remove the ballast resister. The yellow wire will go away when you remove resister and you will need to chase the blue wire to its source. I have two purple on the + side of the coil, but you need to see where your wires go.

The Mark IV block will have a mechanical fuel pump, while the Gen V and VI will be electrical. But then again, based on what we see, the PO could have changed out the mechanical fuel pump, if so, there will be a block-off plate bolted to the block in its place.

 

[Lloyd R]

I have a aftermarket electrical fuel pump. The blue wire goes from the + coil solenoid to what looks like a oil pressure switch on the side of the block.
There is a block plate in place of the mechanical fuel pump.

 

[Mc Tool]

I'll bet the previous owner used the wrong coil and added the ballast resister.

Thats what I figured too,