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What is the normal voltage range after the ignition. I'm reading anywhere from around 10.5 to 17 volts inside the cab of my '66. Is it possible I need to replace the voltage regulator? My CB radio recently got zapped, I wonder if it had something to do with these readings. Thanks

Dellman,

Voltage measured anywhere in the circuit when the system is charging should be in the neighborhood of 13.8 volts.

If your rig isn't doing this, you need to check all the components of your charging system...generator/alternator and regulator is you have one.

17 volts is enough to kill almost anything on your truck and 10.5 is a warp five discharge. What are you measuring this with...something doesn't make sense.


Stuart

I am worried. I am measuring this with a cheap dash mount voltage meter but I also hooked up my shop meter and it gave exactly the same readings. I had the alternator tested professionally and results were good but possible they would miss something like this. I am a little stumped.

As Atomarc suggest, something seems amiss and the whole charging system needs looking at. Something else to check...after installing an electric fan on a friend's '39 Chevy, the dash voltmeter started acting crazy. We ground strapped the engine, frame, and body together and solved the problem. Good luck

Well, I guess I will go through the entire system with a fine tooth comb. I'll see what I can turn up. It has done this with different alternators now that I think of it. I also remeber that the headlights will randomly get brighter and dimmer as you go down the road, they probably just need better grounding.

Dellman,

I am guessing you have a SI, or internally regulated alternator on your truck. If it was tested professionally, the results would only be valid if the it had a integral regulator, hence the assumption.

Behavior as erratic as you indicate would probably show up during a comprehensive test, so my guess is that it would be a wiring or connection issue.

If the alternator (three wire) can't 'see' the voltage in the system, it cannot regulate it. It monitors system voltage with the little wire in the DA plug marked #2.

I honestly didn't think, even under full field output, that a stock alternator could pump out 17 volts. It sounds like it can.

Hooking your meter to the battery would be a good test location. Get a 'before' voltage reading and a running voltage reading. These should be in the area of 12.5 and 13.5 - 14.0 volts.

In my estimation, a professional alternator test doesnt include the phrase Auto Zone, Kragen or Pep Boys.

If your alternator uses a external regulator, then giving the alternator a clean bill of health is only 1/2 of the troubleshoot.

Stuart

First thing is to make shure you have good grounds between the engine & frame & frame to body. If it is an external regulator make shure there is a ground wire on the regulator base as they are mounted on rubber grommets. Then take a hard look at the voltage regulator. A defective battery could cause this problem. It is the balast for the system. What part of Mo. are you in.

I tested the output while the engine was off from the battery, it was about 12.5 volts, which sounds good. I hooked the voltage meter to the alternator output and when the engine was reved it showed around 17 volts just like in the cab. The odd thing is that when the engine is idling (around 1000RPM) it shows about 12.5-13 volts. My alternator is internally regulated, unless someone messed up when I ordered it. I ran a heavy 10 guage ground wire from the alternator to the frame without luck. I noticed that when the engine was running, the regulator was making a loud clicking noise, maybe it is bad or needs adjustment. I will see it the DA plug has a broken wire by ohming in out. Unfortunatly the alternator test did involve O'Reillys so I guess it wasn't professional then. As for the battery, I actually replaced it yesterday so I know it is good. I wonder if this high voltage ruined my old one somehow. I live in southeast MO near Poplar Bluff, probably the furtherest away from Kansas that you can be in Missouri.

Dellman,

Great work and great answers. The regulator on a SI alternator is dinky, internal and solid state. It couldn't make noise if it had to. There should be no black regulator on the firewall.

Over charging a battery can ruin it, but you should see and smell it before it's gone. The top would be covered with moisture (acid) and the battery would emit a sulphur smell.

Your DA plug should be marked #1 and #2...not R & F, and it should be located on the circumference, not on the back.

The static reading of 12.5 is good, but the 17 volts is bad. The only thing that regulates this is the....well, it's the voltage regulator.

I'm out of ideas other than having a real life auto-electric shop have a look at the alternator.

If you have a SI alternator, you should have NO regulator on the firewall, as least not one that is hooked up anyway.

Stuart

I think that my alternator is a SI but I also have an external regulator (which was making noise) that is hooked up. The alternator's power output travels straight to the battery connecting at the horn relay (which then goes to into the cab) on the way. Everything is set up factory and is not modified. Maybe I could take some photos that will help explain. I even find my own explanation hard to follow.

Dellman,

If your truck is bone stock, you have a externally regulated alternator and the clicking you heard is the death scream of a bad regulator.

I have linked a good wiring diagram for a '66 which shows it as you have described.

Good luck and let us know how it develops.

http://rmcavoy.freeshell.org/diagrams/66engine_6.jpg

EDIT. If you are not a purist, switching from the DN alternator (yours) to the SI alternator is simple and will get rid of the firewall mounted voltage regulator.

Stuart

Ok, thanks for the link. I actually have the 1960-66 Factory Assembly Instruction Manual which shows all the diagrams. I guess I will check what type of alternator I have and replace the regulator. Most likely that will solve my probems (crosses fingers) Thanks a lot.

I replaced the voltage regulator and that did the trick. I had actually replaced it less than a year ago because I didn't trust the original one. Since it was rather new, the warrenty was still good and it was free! Now the voltage is right where it needs to be and everything is looking good. Now I can get back on the road without fear of a smoking battery. Thanks to everyone for their help!

Dellman,

Good news. Thanks for taking the time to share your success, everyone appreciates it.

Stuart