I was off Sunday and Monday went for two nice rides. Sunday was about 300 miles. Monday was about five hundred. Truck ran flawlessly. With the possible exception of the electrical gauge. Whenever the electric fan comes on the gauge dips into the D side, when the A/C is on it goes even further down. But when I get home and connect the battery charger it shows 80% capacity???
I thought I had an amp meter but now I am not sure, I crawled under the dash and it looks like I have three wires connected to the back of the gauge. I have searched this site and the web for a few hours and am coming up empty...anyone have any thoughts??
By the way, I stopped in and picked a few parts up from the ladies at Mid Fifty in Golden Valley Az yesterday...they are an awesome group and were very pleasant and helpful.

 

There should be NO wires "connected" to the back of the gauge, it should have the main battery wire running THROUGH the loop (no contact with wires). It works on magnetic principles.

 

I'd take a volt meter and check the voltage with and without the load.

 

Ross, I read every post that I could find last night on ammeters....saw the ones you posted and even "Julie".... Then I looked at the backside of a used one on the Internet. Mine looks like it has a volt meter in the original housing. It definitely is different than the "normal".
But even with a volt meter should I be concerned with what the gauge is displaying?
Thank you for any help you can give.
Mike

 

Amp meter or volt meter, you have a problem if your battery is only 80% after an 800 mile run. IMO, the first thing you want to check is the alternator belt. It should not slip when you try to turn it by hand, engine off of course.
If the belt will not slip, measure voltages across the battery with the engine running at idle and above idle.

 

Yep, basic troubleshooting first, measure the battery with the engine off. Measure the battery voltage while the engine is running (above idle would be best). I like to see 14 volts with the engine running. Then check with the fan running. It still should be at least close to 13 volts or more. I doubt it's a gauge problem, if it's been fine until now....

 

If that is actually a voltmeter in place of the stock ammeter, it isn't that unusual that voltage would drop with the fan and A/C on, especially on a hot AZ day. Take measurements like suggested above. Not sure how your gauge determined the 80% capacity? Was it a hydrometer?

 

I am at work now, but will check into this hopefully later today but it may be too hot so I will tomorrow morning at the latest.
The 80% when I got home is not an accurate number...at least I think so.
That number came from my battery charger when I connected it to the battery.
That is a normal number, I have a red top optima battery. Whenever I charge it it always reads around 80% at the starting point. I keep the truck on a charger whenever I am not driving it. If I went home right now and disconnected it and then immediately reconnected it the charger would show around 85%.

 

I checked both the alternator as well as the battery when I got home.
Idle with nothing on 4 amps and 14.3 volts on a fully charged battery.
Idle with A/C and radiator fan on 27-30 amps and 11.7-11.8 volts
Idle with A/C and headlights 2-36 amps and 11.2-11.3
At a low rpm the amps go up to 40-50 and the volts go to 12.5-12.7
I think it's all good but would like to make sure??
Thank you,
Mike

 

Sounds to me like you could use a smaller alternator pulley, What is the amp rating of your alternator?

 

Hello Bob,
The rating is 100amps.
I don't know what rpm that is based on, but I think I read earlier today that at around 3500rpm it puts ot 60 amps.
I don't have a tach but I doubt if I'm normally that high on engine revs.
Thank you for your help.
Mike

 

Voltage will sag a little bit under load with all accessories on but it should hold above 14 volts. Your numbers are way too low, are you measuring at 2000 or 2500 RPM?? Just a few tenths of a volt is a lot, when it comes to charging or batteries. As a rule of thumb any battery needs approx. 2 volts over and above the resting open circuit voltage, to reach full charge. Modern "maintenance free" batteries measure 12.8 volts after resting overnight or after any surface charge removed. These charge voltages apply at 80°, in cold weather (below 0°) well over 15 volts is needed to keep things plussed up.

Like Raytasch says if you drive 500 miles and the battery isn't charged there is a Problem. One often overlooked factor is corroded cables and grounds and connections, even a tiny bit of resistance will cripple any alternator. Always an issue with vintage iron.

 

This explains it better. Alternator shaft rpm is important.

 

Just to be sure we are not overlooking the obvious, I ask the question again . Can you turn the alternator pulley by hand? If it slips by hand, it will slip under load. How old is the belt? Is it a quality belt? And does the belt match the pulleys? And are the pulleys in alignment?

 

Ray, no the pulley will not turn free, yes it is the correct pulley it is a serpentine belt and the belt is in good condition.