So I'm trying to replace my leaky old coil with a new one.

My old coil has this piece of plaatic with tach test on it, and wires that go to poles on the coil. A very experienced classic car shop I trust said it was useless....but ive discovered that my truck wont fire unless I have it hooked up, and I think there's current going through the wires on it.

So, some one more educated than me, what does this tach test clip on thing REALLY do? My shop made it sound like some useless thing id use to run a tach....and that I didnt need it.

 

It doesnt fit on my new coil...which is how I figured out that it doesnt seem to fire without it. I tested that I wasnt getting any spark from the plugs without it.

I can cut the wires out of the clip on and wire them correctly to attach to the new coils poles....but I wanted to get an understanding of with it does before i do anything.

 

The horseshoe is for a coil with this type of positive and negative coil leads.




You can use a little screwdriver from the inner side and lift up on a tab to allow you to remove the wire and clip from each side.


... leaving the horseshoe with nothing connected to it. From there you can reconnect the wires to your new coil, replacing the wire connectors as needed.

So yes, technically the plastic horseshoe is not a necessity, but you still need the wiring

 

Awesome! I really appreciate your help!

Can you tell me what the wires do? I have a red one and a green-blue one, can I assume red is positive and the green-ish bluish one is negative?

 

Those are your positive and negative coil terminal wires.

Wire colors depend on the year of your truck.

If you have the duraspark ignition then the diagrams in these two posts might be of use:

https://www.ford-trucks.com/forums/1...l#post11397098
https://www.ford-trucks.com/forums/1...l#post11724333

According to 74-78 Wiring Diagram Pt2

Blk/Grn is + positive
Grn/Yel is - negative

Unfortunately, those aren't the colors you said you have.

Fortunately, another way to approach is this is that the wire you took of the Tach side of the horseshoe is negative.