94' k1500 starting/electrical problem

i have a 94' k1500 that was working fine until one day i shut it off and 20 min later went to start it and the starter turned the engine over really slow like the starter was dragging real hard so i went and got a new starter and put it on and it started right up BUT then when i was driving down the street my wipers started wiping the window and they were shut off and the tach started fluctuating all over so when i got home it set there for the evening and the next morning it started and after work all it would do was click not like a dead batt it would just click once so i thought it was a bad conn. on the batt or starter but it wasnt well needless to say i was a bit mad and i hit my steering wheel and tried it onemore time and it started so i talke to some people and they thought it was the ing. switch so i changed it and itstill does the samething unless i hit the dash and sometimes it will start and sometimes it will click or crank but doesnt start HELP please it is driving me nuts!!!!!!!!!!!!