Ignition Coil Question
 

Why would someone run a wire between the leading and trailing coils?

Grasp your phone as you typically would but before starting video recording, rotate it 90 degrees. We call this "landscape" and it results in a video that more properly fills a screen instead of a narrow strip down the center. You can then return the phone to its normal portrait orientation for regular use and the screen will even rotate and resize automatically to align itself correctly.

Based on the video, it looks like someone has jumpered the test connector on the leading coil to the test connector on the trailing coil. Why? No freaking idea. Doing so won't result in anything.

to get the tach to work when a trailing coil has failed?

you are right.. i disconnected the wire and the Tach stop working.

Well, that's creative.

it's actually a pretty old trick, one i personally don't condone. if you lose the leading coil you're dead in the water.

So I changed the trailing coils and tach still not working.
have dig further into this.

Verify you are getting spark at the trailing coils.
If not, check the tan wires at the connector for 12V when the key is on IGN.
If you have access to a scope, you can scope the signal wires (uh, white and pink? doing this from memory) to make sure the ECU is sending a signal.