95 Grand Cherokee Laredo starts by itself
 

Not sure if this is the right place for this or not. I have a 95 Grand Cherokee Laredo 4wd with the 6 cylinder. I replaced the battery and put the cables on loosely and it started fine. I only let it run for a few seconds and went inside, I came out with tools later and cinched down the positive cable. I got the negative about 3/4 tightened and thought it sparked. After that the engine started by itself without the key even being in the ignition. It hadn’t done this when I first put the battery in. It runs for about 20 seconds the. Shuts off. If I leave the negative cable connected it starts itself again and shuts itself off then clicks and starts again. I got in and started it with the key and while it was running it tried to start again. (I could hear the started grind) I have heard it could be the solenoid and/or the starter? Any thoughts on this? I’m not a car guru but this sounds odd as I would expect multiple things would have to be involved for it to not only make the starter run but to allow it the engine to run without ignition on.

What is the condition of your battery cables? Follow the sheathing all of the way to the starter for the positive and to the block for the negative. Be especially observant about any touching points to metal or other cables. Ensure that the positive cable isn't arcing to the starter solenoid. That's a good start. Photographs would be helpful when you reply.

If the vehicle not only started (starter) but also ran for some time, the problem is very likely to be the ignition switch.

A tip to prevent sparks and keep from welding a wrench between + and a fender: Always disconnect - first, reconnect - last (and fully tighten). You want to avoid working on + while minus is connected.