WildChicken

Please help! I have been having what seems to be a common issue with uncommon fixes.
Occasionally, the voltage on my 99 Jeep Cherokee will spike to 19 sometimes for only a few seconds and sometimes for minutes. The lights get brighter the fan blows stronger and sometimes the check gauges light comes on. Now, it seems that this may be causing issues with sensors on my automatic transmission. The Jeep still runs and drives but sometimes I will have to manually shift it through the gears. I was told that the alternator didn't have a voltage regulator and that the voltage was regulated through the PCM. So..I replaced the PCM and still had the voltage issues. At that time i put the old PCM back on, did some more reading and replaced the battery temp sensor. Still have issues.
The transmission issue first showed up separate from this after going through some water but seemed to be fine after it dried out.
Also, my A/C just started having issues. The compressor is not cycling. The reason I'm including this is because it looks like some wires related to the AC system have been monkied with. The transmission shop read the codes p0563 and p0705 this time and told me that I need to get the voltage issue fixed first before they do something that I may not need.
As any of you that have dealt with this know.. this is extremely frustrating.
What should my steps be? Also, does anyone have a map and or pictures of ground locations?

BlueRidgeMark

Check your grounds. See my sig, #1.

Also check your battery cables. All of them. Both ends.

WildChicken

Thank you. Blue Ridge Mark. I appreciate your assistance. I guess I know what I'll be doing with the upcoming long weekend. I'll probably go ahead and replace the battery cables while I'm checking grounds. Maybe there's some internal corrosion.

BlueRidgeMark

Yes, corrosion can wick up inside the jackets and do a lot of damage without being visible.

WildChicken

*Update*
My issue has been solved. Unfortunately, not by myself. I eventually took it to a shop who are known locally for being able to find and fix these types of issues. They found and fixed a short in the main wiring harness. I paid them a little over $400 but, I was extremely happy to have the problem resolved.