My 98 cherokee had no power so I checked terminals as usual and that wasn’t the issue. I plugged a battery jumper up and didn’t realize I was supposed to connect the negative to the frame of Jeep for JUMPING (50a). When I turned key forward all the locks cycled to unlock then to lock and so I thought it was getting too much juice. This scared me so I unplugged jumper which is when I saw I had connected the positive to positive and negative to negative (rather than frame)
now it had some lights but no gauges reading, no fuel pump activation so it wouldn’t start. I got it towed into a shop because I thought it was an electrical problem at this point. They told me it could be the computer, is this possible? I recommended the PCM or even the damn fuel pump, but he said it’s not communicating. The relays and fuses are fine. What the hell is my problem? Any help would be appreciated greatly..

 

That's for safety purposes. If there is free hydrogen escaping from the battery a spark could cause it to ignite. Much less of a risk today because of battery design.

IIWM the first thing I would do is figure out why

 

Not a whole lot of information to go on. Check the battery voltage to see if that's the problem or it's not getting voltage out. There are a lot of simple things you should have checked before you towed it to a shop.

 

turning the key on unfortunatey means there is a good chance your PCM is fried, and possibly other polarity sensitive devices such as radio, TCM

your alternator will have the diodes burned out

I assume you have checked any fusible links, plus every single fuse

 

I don't think there's a problem with the PCM because all he did was connect the jumper cables to the battery instead of the negative clamp to the frame. No cross polarity. If you've ever done that you get a BIG spark unless the battery is TOTALLY flat.

 

As long as you didn't mix up the cables (red to black, red to black), you should not have fried the PCM, unless there is some other electrical issue. That being said, lets see what the mechanic you had it towed to says. If he comes back with some crazy number to do a lot of work, maybe get a second opinion before you have it done. Do you know the mechanic that you took it to?

 

I had the same problem with my 93 Cherokee and it ended up being the alternator. We got a new one from o’rielys and she started right up after charging the battery for a few hours after leaving the ignition on for a while.

 

sorry I misread the OP, so long as polarity is not reversed, there should be no automatic destruction of anything.

I usually jump terminal to terminal, and have many vehicles.

it is not impossible a transient spike has not destroyed a component though, and that component would be electronic as they can sometimes blow before a fuse

 

Honestly, as long as the battery isn't totally drained of liquid, or frozen, or some other glaring defect, you can usually jump terminal to terminal no problem. I usually prefer to do that vs try to find a suitable ground on an engine nowadays.