I have a 1994 Nissan pathfinder and it won't crank but lights and all come on. What could this be?

It doesn't take much power for the lights to work. It sounds like a weak battery. First thing is to use a volt meter to test the battery. You should have 11-12 volts when not running. If its lower it needs a charge. You can also jump start the car and then put the meter on the battery. If it isn't in the 13-14 volt range, your new alternator is not working properly. Hope this helps, report back with any other questions. Alex

Why was the alternator replaced? .. Was the charging system tested before hand?