Look atop the top front center of the rear differential pumpkin for the rear ABS speed sensor. It's attached with one 9mm fastener & it's body has a "O" ring seal.
When my P0500 code popped up, I had a lit ABS light & the cruise control would sometimes not set, or would sometimes drop out, if set. Anyway it's internal winding was shorted & replacement fixed my rear speed sensor woes & fixed the cruise control problem.
My new sensor measured 1.9K ohms, so before removal, you could disconnect its electrical connector & measure its resistance to see if its faulty. If its ok, check the electrical connector, pins sockets & wiring to it. I'd not ignore this trouble code as it'll affect the ABS action.

On the power delay relay code, I found mine located in the dash channel just to the drivers side of the glove box. It was in a plastic container & mounted to the metal dash frame on a bayonet tongue to hold it in place. Replacing mine fixed my intermittent power window woes. It also controls the dome lights, power windows & some other things.

Now, back to the stall tests, when you had the ELM on & monitoring the TPS, were you opening the throttle like it would be if you were moving off from a stop, or were you just wiggling things with the throttle closed?

 

 

Well lets think about this some more, did you test the TPS sweep using a Analog meter, being careful to watch its resistance value for drop outs Just as the throttle begins to move/open?
A digital meter, or the FORScan display may not be fast enough to spot a dead spot if it's really narrow. The failure mode you described, of it stalling as you normally go at throttle up, but if you Quickly go to WOT at throttle up, it won't stall, so that suggests if you go far enough quickly enough at throttle up, you can get past the trouble point & the computer is able to adjust fuel trim quickly enough to keep it from stalling.

Another thought in this stall scenario is a dirty MAF sensor, that's lazy in detecting the increase in air flow as the throttle is slowly opened, when you go at normal throttle up.
But if you go at WOT Quickly, its able to detect the sudden large increase in air flow.

If this puppy has a MAP sensor, maybe it, or its plumbing are some how corrupt such that its not able to respond to the pressure drop of a slow opening throttle but can detect the sudden pressure drop of a WOT???

 

 

When last was the MAF sensor cleaned.

 

I replaced the mass air flow sensor December of 2017 with a Walker Sensor only part# 2452039 from Rockauto. Then in March 2017 with a Ford part#F67Z-12B579-BBRM remanufactured complete unit with sensor. So I still have my original one and the Walker replacement one. I guess I could always try one of the old ones since they may not have even been bad because it never fixed the problem. I also looked at the parts store and they didn't have an analog multimeter. But I'm curious if it's the TPS causing such an issue why would it also start to randomly miss when idling. It must only do it at idling because it's got normal power throughout the driving range. At a stop light, stop sign, or parked idling, you can hear a random miss through the tailpipe and you can look at the engine and tell too. However, it doesn't do it all the time. We also replaced the fuel injectors back in February of 2017 with a matched set of Motorcraft which I think were Bosch or Denso. One of those codes on the GEM module was for LH Power window circuit failure and my truck never even came with power windows.

 

Since you seem to have solved the thread title of secondary ignition wiring break down problem, by using OEM Motorcraft parts, this thread should be closed out & a new one begun for the engine Stall when going at throttle up & the miss at idle woes, so you get Forum answers just for them.

The putt putt sound you hear at idle in the exhaust pipe is the Good reason your old time Tech strongly suggested the cylinder leak down tests.
I haven't looked at what the latest FORScan version can do, so have they put up a version that'll do a "cylinder balance test" yet? They had indicated about 5 years ago that they were going to do that.
My old Actron CP-9145 scan tool will perform that test, so if you can borrow one of those, or another model that will, it could quickly find which cyl/s are likely at fault as they would show a larger rpm drop when the scan tool disables that cylinders fuel injector.
That low side vacuum reading & slight idle vacuum wiggle noted in the video is another clue that he's likely right to do the leak down test.
Anyway close this thread out & begin a New thread for these problems.