I gave my 97 Nissan PU, with 59,000 miles, a treat this morning. I
replaced the original spark plug wires, distributer cap, and rotor with
new items bought off the internet.
The new wires were NGK (pretty blue color), and both the rotor and cap
were YEC (Yamaguchi). The spark plugs were recently renewed with NGKs.
This distributer has no coil wire. There are only the 4 spark plug wire
connections.

Inside the old distributer cap, there was a coil spring around a molded,
tapered post inside the top of the cap near the edge. The wider diameter
at the base of the post held the coil spring by friction. I set the old
cap aside on the air cleaner cover while I replaced the rotor. I went to
get the spring from the old cap to put it in the new cap and it wasn't
there. Apparently it had fallen out during its trip from the distributer
to the air cleaner cover. I checked inside the distributer base (no room
for anything else in there), the engine compartment, and the driveway
under and around the truck, with no success. My driveway search was
hindered by fallen leaves on the driveway, which I gingerly pushed aside.
The new YEC cap came with 3 new screws for the cap hold down, but no new
coil spring or gasket.
The coil spring was longer than the post it sits on so it supposedly
touched something on the distributer base. I checked inside the
distributer to see what purpose that spring served and could not see any
reason for it. If it touched metal on the dist. base it could not make a
ground connection because the top of the spring did not touch any metal,
just the molded plastic (bakelyte?) tapered post.
Anyway, I finished the installation without the spring and started the
truck, and it seemed to work OK. I then took it for a drive and it ran
perfectly without the coil spring. Anyone have any idea of the purpose
of that coil spring?