Was running good then starts running rough. I thought carb adjustment, bad spark plugs or wires, dist cap, points, bad gas, etc. It turns out (I never made the connection until now) but every time I charge my battery, It ran better. Took me a while to find out. I thinks it must be alternator. Ammeter needle does't move with headlights or move at all, remains neutral position. Battery starts engine, but I think it gets so low that it doesn't provide enough juice for a good spark after sitting for a couple weeks. Engine cranks slowly, but maybe I'm wrong. You'd think if there was enough amps to crank the engine enough to start it (though slowly), that there would be enough juice for a decent spark. Where is the voltage regulator? I have never replaced that either. Should I replace both? How do you know it is alternator for sure? unplug the battery while it is running and if the alternator is working it runs if not it dies?
Any advice greatly appreciated!

 

Arrrr!

NEVER disconnect the battery whilst the engine is running to test the charging sysytem!!! That will cause a voltage spike that could fry sensitive electronics... mebbe yes, mebbe no on our old vehicles, but why chance it?

Ok. With a fully charged battery and the engine running, check the voltage on the BATTERY POSTS. You want to see ~ 14.5 VDC. If you don't read that voltage, put yer DVOM prongs on the BATTERY CONNECTIONS and read the voltage. If any different, or even if it's the same, take the terminals off (with the engine NOT RUNNING) and clean 'em good. Mebbe do this first....yes, clean 'em up first before you charge the battery.

Eh, I get ahead of meself sometimes....

Let's try this again....disconnect the battery terminals....clean 'em good. Charge the battery.
Whilst the battery is charging, clean the terminals, then ohm out yer (+) and (-) cables. You want to see little resistance. Physically bend the cables to check if there's any hard areas. This will tell you if there's any corrosion in the cables.
I would say to do a voltage drop test on these cables but you need power for that.....the battery is charging now, after all.

Pull the regulator plug/connection. - depending on yer MY, it could be on the core support or the right fenderwell. Check/clean the connections.
There's a little rectangular dealie on the right fenderwell with 3(?) wires on it - that's yer horn relay, not the regulator.

On the regulator plug - the 'F' connection goes to the FLD terminal on the alternator.....eventually....but the alternator output goes from the BAT terminal to the battery side of the starter solenoid (which connects to the battery) through a fusible link.
You could check/clean this wire....

Now comes the actual troubleshooting the alternator part...IF the battery is fully charged.

With all yer connections checked, cleaned and hooked back up, connect your DVOM to the battery, set on voltage - 20 VDC.

What are you reading?

Have a jumper wire handy - long enough to go from the alternator to the BAT (+) side.

Fire her up

With the engine running note the voltage readings.....then unplug the regulator.
Connect the jumper wire to the FLD terminal of the alternator to the BAT (+) terminal.
You're now "full fielding" the alternator and the voltage should spike to ~ 18 VDC.

Read yer DVOM - if you're reading the spike, the alternator is good and the regulator is not so good ....... ONLY IF YOU'RE NOT READING ~ 14.5 VDC ON A FULLY CHARGED BATTERY WHEN THE ENGINE IS RUNNING!

Hoo, boy....mebbe there's too many syllables here and might get you confused. I'm not normally one to run through the whole testing procedure 'cause it could be too much to do at once. Troubleshooting is a one step at a time deal...otherwise how would one know where the illness is an what to do to correct it....

Get back to us with some results, yes?

 

I'm curious to know what year your truck is... any other background info you want to add? Is there anything odd or unusual about your set-up?

 

Unless you want to stay "all original", I'd suggest doing the 3G alternator swap. Check it out under the "Read this First" stickie note by Hio Silver.

 

Excellent advice that is good stuff to know. I’ll check those readings with the multimeter and get back this what I find. I have replaced the battery cables and cleaned the contacts recently and the battery is about a year old. It’s been drained a few time but it has always charged back up. Has distilled water
Thank you.

 

Sorry guys, its been a while. Was finishing with Energy Suspension bushings all the way around.

Well, my voltmeter was left on so out of batteries, so I wasn't able to check those readings.

Alternator looked like original and Pep Boys actually had one in stock so I took a chance and thought I would just replace it.

Changed the alternator to a nice new one and problem solved, runs fine again.
Thanks for your replies.

 

Glad to hear you solved the issue.

 

You can't trust an original ammeter. Most of them barely moved when the truck was new. Put a voltmeter in it if you want to know what's going on. I also highly recommend a 3G and have done a few conversions, pretty simple. But on the other hand, my 59 still runs a generator because it does the job.