A couple weeks ago i got my batteries and alternator tested and batteries were good but alternator was bad so i replaced it and all was fine. Ive been runnin my truck without a grid heater so i used either to start it which i know isnt good and i dont drive my truck everyday so i only had to use it twice. Now today i got my new grid heater relay and my truck has been sitting since sunday. I put the new relay on and gave it a wait to start light. The crank was strong and i turned jt over for about 5 seconds turned the key off and gave it another wait to start. This time i turned the key and basically the batteries were dead. I have no clue on whats going on

 

On the Second crank did it turn over or nothing at all????

 

Did you actually check the batteries to see if they were dead or it just didn't crank? It could a electrical problem somewhere. They are a tricky sob sometimes. Been there!

 

I did come to find out the way i hooked the relay up was wrong so im thinking that drained the batteries and on the 2nd time it did crank but very little juice

 

Id charge your batteries...Double check your wiring woes.... and crank her up bud.