It appears your old hot tub was wired for a 110 volt circuit and a 220 volt circuit. Your “new” hot tub looks to be wired with two 220 volt circuits, hence the extra wire. Here is the wiring diagram that should help. It says the subpanel is provided with the tub so hopefully the previous owner can give it to you if you don’t have it.

That's what I was wondering. So, I'm going to need to add a breaker to that subpanel and wire to that breaker in order to match what is needed? Thanks!

It needs to be wired per the wiring diagram. There are different ways to do it. If you don’t have the sub panel I would recommend buying the Hot Spring one on eBay to keep it simple. It would be a Hot Spring Spa 50 amp Watkins sub panel. The sub panel should be located close to the hot tub. The breakers are gfci.

I'll head back to the owner's house and see about getting the sub panel. I hadn't realized the difference, I guess I was hoping the wiring would just fit since it did from my 1st spa to my 2nd spa, but evidently not for this 3rd one. Thank you for the help!