Know we have been round with this. In my Harley electricial diagnosis manual. It says the third connection on the coil measures current on the secondary circuit and is used for knock detection and misfire report.

It also says with a NOTE . Engine will not spark with both spark plugs removed. When checking for spark, use SPARK TESTER (Harley No HD-26792) with both plugs installed.
This could only apply to my 2004 Softail.

 

(with respect) You guys are all either really gullible or overly helpful.
OP changed out his motor(engine) yesterday and now can't find fire on a spark plug?

Pulll-leeze !

 

OP appears to be a trout fisherman.

 

Maybe trowser trout?

 

You need compression on the rear cylinder for the plugs to spark.. It has nothing to do with ion sensing but everything to do with how the ECM figures out which cylinder is on the compression stroke.

 

That sounds good but just how do you think ECM knows that. Service manual says leave both plugs in but not that you need wires on. It does however make a safe since to always have wires with a source to ground.

 

Ion sensing, ask your wife to hold the wire, how to ground the plug to the cylinder, put your tongue on the wire.... this thread keeps getting better.

 

Slowing of the crank through the crank sensor. Having both plugs in is OK. ECM know when either piston is at top dead center by simply knowing where the no gap is in the crank. It needs to figure out where the compression stroke is.. Try it on a working motor. Front makes no difference. The reason for sensing rear is that you'll have an extra 45 degrees of advance if the ecm sparks the front.