if your ignition coil is old you may wanna test the resistance on it. some of what you're describing sounds like it could be bad.

 

I agree, check that coil, something is causing your wires to fault, they don't just keep going bad.

 

that's another part I would go dealership on too. I've bought two bad ones from parts stores. I know some guys say they've had good luck with other brands, but I don't know which brands they are.

 

The distributor cap and rotor are less than a year old. I bought this truck brand new, so I know all the history, and the coil is original. 1997 with 240,000 miles. You all recommend I change it? Factory Mopar, or NGK, or ???

 

Not really, I would recommend you test it first, no sense in throwing away a good coil.

However, I have installed a MSD Blaster coil on mine and have had good luck with it. It's a little beefier of a coil and with 8mm summit wires its been running excellent for over a year now. So. If you find your coil is bad(stick a meter on it for proper resistance) then you can go OEM from stealership or maybe choose the MSD, your call there.

Also, when you test the coil. You need to test that thing cold and hot if I were you just to make sure its ok in both conditions. So I would test the resistance while its cold first. Then if that checks out, run the truck up to operating temps for say 10 minutes or so, drive around, whatever, then test the coil again for same resistance. You don't want the coil to fool you when its cold

 

Another thing I mentioned in my last comment that I didn't see you comment on.

You said your wires were bad. Where are they bad? You should see a dark spot, or a crack in the wire or boot somewhere. I doubt they degraded inside in so short of time. Unless they were really cheap wires. But even still, doubt it. So if they have a crack or bad spots on the wires, where are they located? You may still find that the wires are sitting on metal somewhere and not properly held up thereby causing them to heat, crack, burn, etc in those spots and there you may find the issue. I would look there at the same time you check the coil. 9 times out of 10 a bad wire is caused by heat and/or laying on something they shouldn't be.

Good luck.

 

Apologies, I just re-read your original post and saw this:

"Also, it seems every 2 years I need to replace spark plug wires. I route the wires very carefully (according to the TSB, even going above and beyond)"

I would still check them out though. You never know.

 

I tested the coil (cold), and between the bottom two pins I got 0.8 ohms. Using the top tower and going to either one of the bottom pins shows me "no circuit".

Does that make any sense?

 

Generally speaking, most automotive coils will have a resistance reading of about .7 - 1.7 ohms for the primary winding and 7,500 - 10,500 ohms for the secondary winding.

Need to find the coil specs from the service manual and check what they need to be. I don't know off the top of my head. If they fall out of spec just a little bit then its a bad coil. Coils are sensitive components.

 

Here is a good article on how to test the Dodge Ram coils.

http://troubleshootmyvehicle.com/chr...gnition-coil-1