starter problems

My starter just started to "click" when the key is turned (one loud click)so I had it checked and was told it was good I reinstalled it and the same click so I took the battery out had it tested and it tested good so I went and bought a new starter. The same "click one time" If you it out and have someone turn the key it will spin but lacks any power.. The jeep will roll start fine but not jump-start??? If anyone can help please I would be greatfull...1992 jeep wrangler 4.0L

Sonds like your battery cable may bad. Replace the cable from battery to starter.

Shoud I check the ignition wire to the seleniod also or is it good because it's making that "click" also is there any way to check to see if it is grounded??? Thanks for advice I'll try it.