I went looking for new plugs for my '97 5.0, they are MotorCraft# AWSF 32E that are hard to find, they crossed over to NGK #TR55IX platinum so I bought them. When I compared the two the MotorCraft has a shorter thread section, then I saw they have a tapered seat and the seat was in the same relative place. I search here and other forums to find that Ford has abandoned the original plug design and this longer threaded plug is the approved replacement.
I just wanted to pass this along.

 

I believe I'm running the same plugs in my '00 Mounty and they're working pretty good, 10,000 miles later.

 

I was unable to replace mine, I had the wrong plug wires! The plug wires are special to that motor and they sent me a generic set for a 5.0, the proper ones have clips for the coil pack and at least 1 wire has a metal shield near the boot.
Hopefully I'll be able to get them replaced this week.
When I ordered the parts I had no idea the plugs were so expensive, I was used to paying under $20 for a set of NGK and about choked when I saw the bill. I guess they are OEM or better caliber, no problem with that.
I believe I'll replace the inner fender splash skirts while I'm at it, wirebrush the rusty stuff and repaint the inside.

 

http://www.allfordmustangs.com/forum...r-threads.html

-Motorcraft AWSF32E - Alternative Spark Plugs-

 

Correction, I'm not running NGK plugs, but Autolite XP104 plugs (also iridium) for $4 a piece on RockAuto. I also replaced my inner fender shields for about $6 per side. For plug wires, you have some options. Motorcraft set is available, so are Taylor wires, just depends on how much you want to spend... plan on $80-130.

 

Yup, the plug wires are salty, as I learned. Sometimes you spend lots of money but can't see it, when you see and feel these wires you know you paid a fair price. My truck has just under 100K miles & 20 years on it, the original stuff lasted this long, best I replace 'in kind' and they might outlast me.

 

I dunno what all the hub bub is about with the spark plug for a 5.0. I just use the basic champion copper core cheap plugs. They work fine and since I have a hole that burns oil and deposits it on the tip I change at least that one a couple times a year. No special plug needed. You're over thinking this.
I did invest in some monster wires for my plug wires. They weren't cheap and I had to buy boots to protect the plug ends from the manifold heat.

 

The EDIS8 ignition is about twice as hot as a standard distributor ignition and it's also waste spark, so each plug fires twice as often as it would in a standard ignition. That means that a standard copper plug will erode in half the time it normally would. The spark gap spec is wider as well because the ignition really is that much hotter. That's the only reason Ford specs a platinum/iridium plug; slightly better material lasts a bit longer. Now if you've got engine problems and it's worn out, I can see not running them, though.

 

I understand all that and I've tried them all. No difference. 237k miles and still runs great. I'd drive it anywhere. Wore out? Nah, just broke in.