2004 Ford Focus (occasionally) won't start

Short version of the problem:

Occasionally my 2004 Ford Focus will not start. I put in the keys and turn them. The lights and radio fire up and there is a click, but the engine won’t turn over. To resolve thisI remove the key, open the hood, loosen the battery cable on the positive terminal, wiggle the cable around, and then tighten it back down. I then go back in the car and turn the key. Voila! The engine starts.

Is there a bad connection somewhere? Should I replace the battery cable?

Long version of the problem:
I’ve been having these problems intermittently for almost a year now. After the first or second time I had the car towed to a local shop. They couldn’t figure out what the problem was because the car was starting just fine at the shop. The mechanic said that some of the cables might have shifted around in the towing process. So I tossed an adjustable wrench in the glove box in preparation for the next time. The next day, it happened again. Through some quick trial and error, I narrowed down the problem to be the positive battery cable (or something that’s connected to it).

I humbly submit my problem to the wisdom of the community.

Since you can make it work jiggling the battery cable, it could be that there’s a bad connection between the starter and the battery but it is more likely to be the starter - 9 times out of 10, when you hear just a 'click, it usually is the starter.
Do inspect the fat cable to the starter to the battery. It could be that the wire isn’t clamped into the terminals very well, for instance.
If you find nothing wrong, next time it happens, get a piece of 2x4, put one end on the starter and whack the other side with a hammer or your shoe. If it now starts, your starter (the solenoid on the starter, to be precise) is suspect.

The first thing I’d do if my car is remove both cables from the battery and clean both battery posts and the inside of the connectors that attach to the post with a battery post cleaning tool. Then replace both, tighten them up, and see if that solves the problem. If you don’t have experience with batteries, ask someone who does to help you. Working with batteries can be dangerious. For example, the negative connection should be removed before the positive, etc.

It’s possible it is a starter problem too. But start with the battery, that’s easy to do, & if it doesn’t fix it, then move to other possibilities, like the starter.

anybody has a ford focus with starting problems run a ground wire from the nagative post to the engine cause the starter has a poor ground and has to have a good ground the starter will have no more problems.