My 1978 F100s battery isn’t charging, I replaced the alternator but that didn’t help. I’m thinking next I will replace the regulator but I’m wondering what you guys think, if any of you have had this problem before.

Cheers,
LJ

 

Jack,
Hopefully you own a VOM volt ohm meter. Set it on dc volts and see what the voltage is at the battery,
With the engine running it should be +/- 13.8 volts. This will confirm the charge or no charge issue.
If not, then check for bad connections, splices in wiring.
I always prefer checking and finding the problem source rather than throwing parts at a problem.
I am not a mechanic, nor did I sleep at Holiday Inn last nite but I have attended the school of hard knocks my whole life. LOL
Good luck.
My .02 worth

 

The needle on the amp gauge barely moves, if it's not charging , it will show a discharge, but you have to look close.

 

I do have a volt meter, and when it was running it was only 12.3 volts. After I replaced the regulator it was 14.5 volts.

 

First, glad you got it fixed.
Wonder if that was your original #ad
#ad
problem ?
As BKW stated the factory volt gauge is very hard to read,, That is why I installed a after market voltage gauge.

 

I think it was the problem, not the alternator. But the alternator was old anyway. I’ll have to look into getting a better volt gauge. Also the engine is the 300 inline 6. I’ve been thinking about putting a four barrel on it sometime.

 

In the Pictures supplied by BlueOvalex (Thank You), you see he is using a Volt Meter. It tells you the voltage in the battery with just the key on to activate the Volt Meter, engine off. Also the voltage being put into the battery when the engine is running and the alternator/generator is putting out at it's maximum capability. Both the Volt Meter and the Ammeter can be read, in different ways, to tell you the health of your charging system and battery. The Volt Meter is the simplest installation and needs one wire to a power source when the ignition switch is turned on and possibly a second short wire to ground if the Voltmeter case doesn't do it.

On older vehicles like our trucks you can run the whole electrical system thru an aftermarket Ammeter if you want to, except the horn . The stock dash Ammeter, as stated is basically telltale, it doesn't carry the whole load of the truck. If it it did you would see plenty of movement of the indicator needle. Ammeter's come in various capabilities. Most common for highway use, 40, 60 or maybe 100 amp depending on the the needs of your vehicles total amperage draw if everything in the vehicle was on/being used at the same time. Suggestion by ME, is stock vehicle, 40 amp alternator, 40 amp meter, 60 amp alternator, 60 amp meter. If you have or are going to add some high load accessory, may be you need a bigger alternator, say 100 amp and say a 100 amp meter.

If You wanted to install an Aftermarket Ammeter on your vehicle, basics are below, a bit more involved, but not Rocket Science.

At the starter solenoid, Battery cable side there Is/Are smaller wires, one of them feeds the vehicle, CHOOSE That Wire After mounting your aftermarket Ammeter, you run 2 new wires from the Ammeter to the starter solenoid, THEY NEED TO BE the same gauge or a bit larger than the stock feed wire. Mount And Secure The Wires SO They Will NEVER Chaff Thru The Insulation To Metal Anywhere and cause a short, that could cause a fire.

One new wire attaches to the original wire you removed from the starter solenoid. Cut the ring eye and remove, join that wire to one of the the new wires that goes to your new Ammeter, with a proper size heat shrink butt connector. On the other wire you install a heat shrink ring eye, that will fit the stud of the starter solenoid. Attache ring eye wire to the solenoid where you removed the original wire. Do All This With The Battery Disconnected. Just remove the ground cable from the battery and push aside.

Upon finishing your installation, two tests.
1- With everything in the vehicle off, door closed, if you have door operated interior lights, brush the Battery ground cable to the negative battery post and look for any spark. No spark, hook up the ground cable. A better test is if you have a test light, one end of test light to the cable, other end to the Neg battery post. No light, nothing is on. Light on, something in the vehicle is drawing current from the battery. There

2- Reach in thru the window and pull out your head light switch, look at your new ammeter and it should read Discharge. If it reads to Charge, you need to reverse the two wires at the back of the ammeter. Disconnect the Battery again while reversing the wires. That should be it.

A note, Generator Systems don't put out at engine idle, Alternators, with no accessories on will most likely show charge at idle.

 

Hey Cap,
Really nice write up for the amp meter install.
Many years ago, I helped a guy install one in a truck but we also added an auto reset breaker. amperage little more than draw..
He was worried about the interruption if something shorted out,
Like you I told him a little interruption is better than burning things up for a permanent interruption. LOL
Again, Great write up and easy to follow.....

 

Thanks B O, appreciate your kind words. Yes on circuit breaker for an added safety if one chooses . I really tried to emphisize the need for good routing of the two added wires to prevent a short, as you wouldn't normally find a whole system breaker, I have never used one. Another thought as I write this is of a fuseable link. ???? I know there are some in harneeses from factory in some installations but not sure they are for whole system.

Nice neat install on your gauge's, they look good.

Thanks again, Cap