OBD2 plug port?

That six-pin plug is for the scanner / code reader. It looks like a 1" by 1 1/4" rectangle with a small square cut out in one corner. Chrysler makes retrieving codes real easy. Cycle the ignition switch from "off" to "run" three times within five seconds, then count the flashes of the Check Engine light. They are two-digit codes. There will be a series of flashes, a short pause, then a series of flashes for the second digit. Next is a longer pause, then the next code will flash the same way. The last code will be "55" which can be ignored.

There's lots of scanners that will work. I have a Monitor 4000 updated to 2002 but it works on newer models. I also have the Chrysler DRB2 which was designed for your truck, and I have a newer DRB3 what works all the way back to '83 models with the right plug-in cards.

Inexpensive code readers are available all over the place but they don't do anything but read codes. The scanners display live sensor data and you can activate various relays and solenoids to perform tests.