I've got a 1999 Dodge Dakota Sport V8 5.2L 5 Speed Manual.
From the looks of it, the previous owner of the car had tried messing with the cruise control. It does not work, the light on the dashboard doesn't come on for it when I turn it on.
I'm looking to see if anyone has any diagnostics that I can try, or a wiring diagram for it.

 

Power is supplied for the system via the PCM.

Does the horn work? The switches run through the clockspring and it can fail.

Is the brake light switch properly adjusted/working. There is a separate set of contacts in it for the speed control.

All the switches are multiplexed. If you unplug the connector to the clockspring you should see differing resistance values as you close each switch.

I've attached the 2000 schematic. It's almost identical to your '99.

 

You can read my thread on installing cruise control on my truck that didn't come factory. I included tests and everything to verify (such as button ohms). Mine however is a 98, but should be similar. Also, did you mean V6 3.9? Grab a build sheet from Dodges website and see if it came factory with it, if not, the light won't work but the system will.

https://dodgeforum.com/forum/2nd-gen-dakota-tech/408980-adding-cruise.html

 

The horn works, all the fuses work.
I noticed that the violet and red wire with the 4 amp fuse is disconnected from the brake peddle. I don't see where they are supposed to be connected.
I've got four wires for my cruise control switch. I don't think they run through the horn. I can see where they connect.
This is the wiring diagram that I believe to be my cruise control.

 

Test the switches. If the clockspring goes bad, all it takes is for one circuit to fail, and none of them will work.

 

+1 For testing the switches. When I put cruise into mine it didn't work at first. Turned out the switches ohm'd waaay out of spec. Simply had to yoink another pair of switches from a junkyard.

 

I'm not the greatest with electrical. How would I test for the right ohms? I know how to test to see if the switch works. I just don't know how to test for the correct amount of ohms.

 

The values for the various switches are known, so, you simply put your meter on the correct wires, set it for the appropriate range resistance, and press a button. If the value is correct, that one works, if the value is NOT correct..... you just found your problem.

 

The switch appears to be in good shape. I took all the wiring for the cruise control out. There are two wires that someone spliced into two wires on the PCM. I am not sure what they are for. Does anyone have a PCM wiring diagram for a 1999 Dodge Dakota 5.2L V8 Manual 5 Speed?
Also, where would I hook up the VSS to? I don't believe my transmission has one (Could be wrong).

 

Your truck uses the rear wheel speed sensor on top of the rear diff for vehicle speed.