ok guys i got a good brain buster for ya, truck runs fine, when im runnig after the grid heater finishes cycling, i noticed when my heater is on im running a tad under 14 volts, when i shut the heater off im running a tad over 14 volts, evrything seems to be running right, any ideas, should i be worried

 

Hmmm, check all terminals for corrosion, might even have the charging system checked out and the batteries load tested.

 

brand spanking new interstate batteries less than 100 miles with new battery cable that strings two together, when the heater is on the volt guage is a tad below 14 but i hit the throttle and it goes back up, something not making sence here its only when the heater is on is when it does it

 

the heater pulls a ton and will make it cycle hard.

 

Might want to have the alternator tested.

 

Brushes might be on the brink of being worn out.

 

in the alternator? how much does a new alternator run that is bigger than stock?

 

Another thing that controls the charging circuit is the battery temperature sensor on the left battery. I notice when its colder weather, the charge stays above the 14 mark for a little while. Summer time it rarely gets to 14. I have a newer alternator as well.

 

If it's ONLY the heater that does it, I find it hard to believe the alternator is going bad. With all the lights he has on there (and assuming he checked the gauge with them on), it should have dropped the gauge some. The fan shouldn't draw enough amps for the meter to fluctuate. And since it ONLY happens when the fan is on, start there. I'd do like suggested above and check for corrosion on some terminals. A poor connection will cause enough amps to be drawn that it can start overheating wiring/relays/connectors. Does it draw the gauge down on only the high setting, or anytime it's on?

 

get a volt meter and check the voltage at the battery and compare it to the dash gauge. my brother has a chevy z-71 and the gauge in the truck looks like it has Parkinson's disease but with a volt meter on the battery the voltage dosen't drop a bit. there may be an issue inside the truck, like a faulty ground somewhere, that is making the volt meter read off or that makes the fan motor (i'm assuming you tried to turn the A/C on and see if it does the same thing) work.....