the higher the fan speed the more it drwaws

 

Doesn't sound like a big deal. I wouldn't be concerned. Are you turning the FAN on or the AC COMPRESSOR on? The Compressor will draw a big load on the engine. I always run my heater from the blower fan, and not the compressor.

If you put a voltmeter to the battery when running, see what the voltage is when at operating temperature and nothing else on. Then start turning things on and see what pulls the most load. You'll find that the heater uses alot of amperage, and you can probably find out exactly what kind of amperage draw it should have at all speeds by researching through a manual or somewhere online.

 

The dash gauge will show a little different reading than a meter on the battery, but the numbers you're showing aren't abnormal, especially if you're on defrost and the AC comp is kicking in.

 

The fan does not draw enough amps to draw your battery gauge down alone. No way in hell. Yes it does draw more amps/volts the higher the speed, but it should not be enough to cause a fluctuation in the gauge like you explain. I'd think you would be blowing fuses if the amps got high enough. The fuse is probably, what, 10 amps maybe 20 at most? If you were drawing enough to pull the gauge down the fuse would blow.

 

The actual reading at the battery will not be fluctuating as much as the gauge in the dash. If the meter were hooked to the blower's high terminal it would dip even more. If your gauge was sitting on twelve volts and dipped when you turned the blower motor on, I'd worry about an alternator. It's normal line loss through smaller gauge wires. If you're really sweating it, check your battery voltage at the terminal as you turn the heater on.

 

dont know where the wire for the volt guage hooks to but i bet it is way down the line from the battery or alternator. slight movement and variation of guage would not bother me. i usually like to know where the guage points with key on eng off. then see where it points with eng running and be happy that it stays above the eng off value.

 

Dont worry about unless it just want start. When it is cold outside the heater draws alot. my gauge goes up and down up and down lights dim. until it gets warm then it quits. sometimes if it is around say 10 degress outside. say you shut your truck off for maybe 2 or 3 min then start it again will do the same thing. just the grid heater intake heater. whatever you want to call it. dont worry about it

 

ok just checking because i do have a crap load of lights on this truck