2018 pete 579 tail light problems

Did you check the voltage with a meter to see what, if any voltage, is being supplied to the tail lights? The lights run through a Chassis Node which is on the inner frame rail, driver's side, across from (next to) the fuel tank. It has three 21 pin plugs. There will be one or 2 connections (harnesses) before the tail lights. If there is no or low voltage in the rear then trace the harness from the tail lights back to the next connection.
"Had to switch from the 3 pin to 3 prong" Why? I suspect you were given the wrong parts or bought the wrong parts. So, you rewired new plugs onto the harness to fit the new lights? You may have connected the wires to the wrong terminals on the plug. Could also try a jumper wire from the plug to each pin/prong on the light to see what happens.

 

From Post #2
If there is no or low voltage in the rear then trace the harness from the tail lights back to the next connection.
This should also lead you to the node. Node close to 2k so not something just to throw a part at.
Front lights, rear lights, trailer, even the wipers run through that node. A problem in the node can cause a number of things such as one turn signal not working on the tractor or trailer ....
Don't forget the thumbs up.

 

Here is another diagram. On page 4 see area H - L and 1-7, the top right. Find where the Tail Lamp Harness meets the Rear Chassis Harness, disconnect there and test for voltage. If nothing there then find where the Rear Chassis Harness meets the Front Chassis Harness and do the same. The C on pg 4 in L7 continues on page 3 L10 at the top of the page. Note that from A on the connector at S44 there is Yellow 2411 which branches off at S44 which goes to the front marker lights. If you have marker/park lights on the hood then your problem is from S44 back to the Front/Rear harness connection or further back to the rear from that. Diagram may not be exact but has the white ground and yellow wires that you have so it should work.