Wiring is messed up on ford ranger wires are missing on the engine

Could be a long list of choices.
Nothing special happens when the ac is on other than the extra load on the engine.
You probably have a slight miss-fire most of the time and the ac makes it worse.
A miss-fire could be a faulty spark plug, wire, coil pack, or injector among other things.
Is the check engine light on ?

if you are changing engines you must use everything off the 94 engine

things that can cause it to miss.
fouled plug (checked)
bad wires(checked)
coil pack(checked)
ignition signal to coil pack( switch old coil pack to a working cylinder to make sure its good and you may find a possible short in the wiring to the coil pack) alternately check the voltage to the wires going to the coils make sure like colors have like voltages. im not too big into ford trucks but thats a good start for most vehicles
possibly injector stuck open and flooding cylinders
timing could be off

o2 sensor is often overlooked

Changing the spark plugs is a pretty easy task. The spark plugs run along both sides of the engine (if its a V block) , 1 per cylinder. You can easily identify them by the plug wires running to them from the distributor. Pop off each plug wire, (1 at a time) and replace the spark plug. Once you have replaced the plug, replace the plug wire. This ensures that you dont mess up the sequence of the wires which determines which cylinder fires at what time in the cycle. VERY important not to mess up the sequence. If you should happen to get the wires mixed up, look online for the firing sequence for your vehicle and engine.

You should be showing the check engine light. Rent a scanner, read out any code(s) and pursue to repair(s).

the fuel injector may be faulty in that cylinder

I would start be replacing the plugs and wires. Sometimes the wires start to break down on the inside and a visual inspection will not help.

Have you or the dealers checked the plug wires? Often when there is high humidty weak plug wires can cause the engine to miss and this is difficult to diagnose in a shop environment. Modern ignition systems have very high voltage and also worn plugs can cause the voltage to spike. This would let the weak plug wires lose the voltage and cause the engine to miss.

If it wasn't missing before you changed the wires, it's most likely you crossed one of the wires. Find out the firing order on your vehicle, this will tell you which one is crossed. when ever you change wires, it's best to do it one wire at a time. Hope this helps.