Car wont start

I have an 89 5.0 Notch with 104k miles. I used to have a problem every once in awhile with the power wire that goes to the starter getting lose or dirty. So I would have to take off the wire, clean the connection and put it back on and it would work fine. Recently it seemed like I had the same problem. Go to start the car, it just clicks once(which im 99% sure its the starter solenoid clicking) then I lose all power. The reason I think its the starter wire/starter solenoid again is bc I was able to have the car pushed and I popped the clutch and the car ran. So I took the wire off and cleaned the connection but the car still wont start. Also I checked all battery cables to make sure they were tight and they are. The thing that is different this time from all the other times is that I lose power after I hear that 1 click when I turn the key. Also the battery is fully charged. So is the problem the starter solenoid? By the way the starter solenoid is less then 2 years old, but I know with electrical, things can fail anytime.

I used to clean the wire that actually goes down to the starter. The only wire located to the starter. I would clean it at the location of the starter where the wire gets screwed down to the starter. I cant really tell if I lose presets bc it takes a while to get power back so I've just been pulling off the ground and putting it back on then the power comes back. But if I dont do that it takes awhile usually.