Hi Fellas,
It's my '65 F250: I've got an aftermarket volt meter installed in my dash where the AMP meter was. I don't think the battery is an issue, as it is not that old. The Voltage gage has functioned correctly for quite some time - until today. While traveling to work this AM, I noticed that the voltage would drop down to ~12.5 V and then after 5-10 seconds the needle would go up to its normal operating level of 13.8 V.

I'm confident the 390 will start when I go to leave work, but there is obviously something not right. I do have a VOM, but I am at a novice level with using it as a tool. Outside of checking under the hood for any loose wiring at the alternator, voltage regulator, solenoid, etc. I will also pull out the dash cluster panel and check the connections at the back of the voltage gage.

Beyond that, (assuming I don't locate the obvious problem) I'm not sure where to go....what would you guys suggest I check next?

Thanks in advance for any & all assistance, Guys!

BarnieTrk

P.S.
It doesn't act like a loose connection, as the gage needle would not react to the truck driving through cracks/seams/small holes in the road....

 

checking for loose wires is a good start.
you could verify the reading on the dash gauge by reading voltage across the battery terminals with your voltmeter.

it sounds like perhaps the "exciter" wire is loose, which is causing the alternator to cycle off/on. just a guess.

 

Well, my truck fired right up when I left work, when I left the gas station, and two more times before I reached home. Once home, I did not locate any obviously loose wires during my inspection under the hood. During the trip home, the gauge did read steady @ 13.8 volts and slowly climbed up another needle width to nearly 14.0V during the hour or so commute back home. So, apparently whatever was causing the needle fluctuations has ceased. Never the less, I'll continue to keep an eye on the gauge during future outings.

Rustywheel68,
Thanks a lot for taking the time to share your ideas! I'll look further into your suggestions during the next day or so.

Carry on, Slick Fans!
BarnieTrk

 

Do you still have the original non-electronic voltage regulator in your truck? The original mechanical style regulator has breaker points inside and sometimes they get stuck. Mine did. Also, when the volts go into decline on your gage is there some kind of a current draw going on that is overwhelming your alternator? And while we're at it, do you still have your original low amperage output alternator? Back in the day many of our trucks came with 35 amp alternators because they didn't have very much installed in the truck that needed much power. Have you added a stereo, or air conditioning, or halogen headlights? Now days people are upgrading to 65 amp, or 100 amp, or more alternators. Just a thought. . .

 

<TABLE class=tborder style="BORDER-TOP-WIDTH: 0px" cellSpacing=1 cellPadding=6 width="100%" align=center border=0><TBODY><TR title="Post 11757482" vAlign=top><TD class=alt2 align=middle width=125>SuperSabre,

Thanks for the thoughtful reply.

Yes, I am still using the OEM-style voltage regulator.

No, no current draw to coincide with the needle drift...I was just driving along with no radio/sound system, no lights, no A/C, no electrical-using gear of any kind.

Good question regarding my Alternator, as I don't know what its amp rating is....Is that info normally stamped on the alternator somewheres?

BarnieTrk



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Your alternator may or may not have its output rating stamped on it. Look on the exterior housing alongside the bottom hole where the alternator mounts to the engine block. You may find the data there. Only in my case, when the rebuilder got through with it, he ground off the output information while leaving other information. It's my guess that my alternator had originally been a 35 amp unit, but it was upgraded to 65 amps. Good luck.