I'm a reasonably good mechanic (on the DIY scale), and I generally do all work myself. However, I needed the starter changed on a 2000 Chrysler Grand Voyager 3.3L, and this guy wanted to do it for a few bucks. I let him.
After it was done. I took the vehicle out. It started OK.
But the speedometer needle never moves from zero mph. The shift indicator is gone (the numbers and letters still light up). The tachometer indicates higher than normal RPMs, and I believe the transmission (automatic) is not shifting out of the low gears.
I speculated the guy disconnected something. (He admits nothing and is not helpful.)

3.3L Chrysler 2000, looking upward and toward the rear.
The big hose is the bottom radiator hose. The oil filter is on the right. Between those is an electrical connector with, apparently, one wire missing. What is it?

Searching on the subject, perhaps the output speed sensor is relevant.

I'm still looking. I still would like to know what the electrical device is that is in the picture.

Added edit: I just learned about "limp mode". The symptoms match. I haven't figured out the problem yet, but I seem to be on the right path.

 

That appears to be the oil pressure sensor and it only needs a single wire it grounds through the block; over 4 psi circuit open no oil light - under 4 psi circuit closed/complete and the oil lamp lights.

Almost sounds as if the connector to the trans solenoid pack is disconnected (just below the input speed sensor).

 

Thank you for providing the information.
I'm going to skip the details of what I did and simply report the current condition.
The car starts and runs. However, the instrument cluster is dead. I previously checked the fuses, but I'm going to do it again. Where is a diagram?

 

It turns out the fuse second from the left in the under-dash box was blown. I replaced it, and now the instrument cluster



Chrysler 1996-2000 Voyager, Interior Fuse Box (ignore drawn circle)