1987 Dodge Dakota Rotary Button

What are you talking about? What button? What symptom or problem?

That's called the "rotor". A "rotary button" is the term often used to describe the heater fan switch, wiper switch, or headlight switch if it's the turn-type of switch. When you talk about the "rotary button" in the distributor, that's the spring-loaded carbon contact in the center of the distributor cap, so you can see why anyone would be confused with your terminology.

You still didn't say what the symptom or problem is. In very rare instances a rotor can become shorted due to a condition called "punch-through". That's a huge problem with the older GM HEI systems that used ignition coils capable of much higher voltages than needed to fire the spark plugs. If you unplugged a spark plug wire while the engine was running, and held it too far away, the spark would find an easier path to ground through the rotor. Once that happens, a carbon track is left behind. That carbon conducts current so from now on spark current will go to ground through the rotor instead of following the more difficult path through the carbon-impregnated string in the spark plug wires. That results in a no-start condition.

On most other ignition systems, yours included, the maximum voltage stock ignition coils can produce isn't usually sufficient to cause punch-through, but if moisture got inside the cap, that can conduct the spark current and cause carbon tracking too. Often you can't see that so it's easier to just replace the cap and rotor. The clue is you'll have good spark at the coil wire but not on the spark plug wires.

You can also have a single-cylinder misfire if there's a carbon track inside the distributor cap near just one terminal. That almost always starts out from moisture. Cleaning the cap is rarely a permanent solution.

There was also a real common problem on Chrysler V-6s and V-8s in the late '80s / early '90s with worn bushings for the distributor shaft. The symptom was erratic idle speed due to rapidly-varying ignition timing. If that was ignored long enough you could get misfires due to the reluctor moving too far away from the pickup coil to induce a signal voltage. You would find that with a timing light. The timing marks will be bouncing around pretty badly.

If I "gave it to you", that wasn't my intent, ... Sorry. You still didn't say what the problem is that you're trying to solve. If you're looking at the brass or silver metal tip on the rotor, there will be a gap between it and the contacts on the distributor cap. That's normal.

Do you have spark at the coil wire? If you do not, we have to determine if the automatic shutdown, (ASD) relay is turning on during engine cranking. You can determine that by measuring the voltage on the smaller ignition coil positive wire or either small terminal on the back of the alternator. You will see 12 volts there for one second after turning on the ignition switch but you might need a test light to catch that. Most digital voltmeters don't respond fast enough. What's important is if that voltage comes back during cranking. If it doesn't, the most common cause is lack of signal from the pickup coil in the distributor.

As far as I can remember, I never solved a no-start problem on a Chrysler product by replacing the rotor or distributor cap. There's really no good way to test them. We just replace them.

The ASD relay is bolted to the left inner fender. I had a recent major house fire so I'm typing at the library and don't have access to my service manuals, otherwise I'd tell you which one it is. The starter relay will have fatter brown and red wires, so it's not that one. If you find that 12 volts on the ignition coil's positive terminal for one second after turning on the ignition switch, the ASD relay is working and the Engine Computer has control of it. If that voltage doesn't come back during cranking, that's when you need to look at the cam and crank position sensors. I can't remember if your engine uses a crankshaft position sensor or not. If it does, it will be in the transmission bell housing right behind the right cylinder head. It has three wires, and it's spacing is critical. If you remove it, a new thick paper spacer must be used when it is reinstalled. My daily driver is an old '88 Grand Caravan. It doesn't have a crank sensor but later models did.

The camshaft position sensor is in the distributor, under the rotor. It's a Hall Effect Switch which is a transistor that is switched on and off with the presence of a magnetic field. I don't recall ever replacing one of this style, but on the four-cylinder Omnis, Horizons, and Shadows, these were a real common problem. Many people carried spares in the glove box. If the signal is missing from this sensor, you should have a diagnostic fault code related to it. Do you know how to check the fault codes?