[Shop-talk] electrical problems with truck

[Jimmie Mayfield]

On 8/5/21 10:33, john niolon wrote:
> with the a/c on, headlights on and elec radiator fan running (as much 
> load as I can put on it)... the alternator o/p at 14.5 volts, the 
> voltage at the terminal on rail reads 11.5 volts.  The terminal is 4' 
> from battery and fed with #4 stranded wire.

I think this might be the smoking gun.  The voltage you're seeing at 
that terminal with the engine 'on' is roughly what I would expect to see 
if you were powering things only with your battery.  But let's check 
some things before I jump to conclusions...

1. Double-check the electrical path between this terminal and the 
battery/alternator to make sure there's no corrosion that might increase 
resistance.

2. What's the voltage at the terminal with those accessories 'on' but 
the engine 'off' ?

3. How big is the alternator?  Do you know offhand what its rated output 
is at various engine RPMs (some aftermarket manufacturers provide this 
info).  Sometimes folks with big audio systems will run into 
dead-battery problems after installing a high-output alternator because 
the new alternator's 'preferred' RPMs don't match up with the owner's 
typical driving style.

-- J



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