charging system question

[lostmya]

I recently installed a voltmeter in my pickup and noticed that anytime turn on my headlights, wipers, turn signal, etc. etc., my voltage instantly drops from about 14volts to about 10 or 12volts. I have a brand new optima red top battery in it so I doubt it has anything to do with that, so could this mean I need a new alternator?

[Green Machine]

Might depend on where you voltmeter is wired into. Could have some bad grounds, body to frame, engine to cab, battery to frame or body etc, common problem, you can never have too many grounds. Get a good handheld voltmeter and check voltage right at the battery. You should hold about 14.5 volts at fast idle, load or no load, maybe a little less at idle depending on the alternator capacity. If not, then you have a charging problem.

[Longhorn Man]

you need to actually test it on the battery for troubleshooting.

[Andy4639]

What kind of alternator do you have...external or internal. Do you still have the old external voltage regulator hooked up. Checking the charging system is best done at battery as stated. Have you checked the belt tension on the alternator lately? These are all things to check and the grounds too!

[Wrenchbender Ret]

Sounds like you have a low output alt. or it has a bad diode. You should have at least a 65 amp. The amp. rating is stamped on the drive end housing near the ear for the adjustment bracket.

[ChevLoRay]

Didn't these trucks have 37, 42 or 61-amp alternators when they were new? I know there are higher-amperage alterntors, but anyone of these are going to be stretching it to keep up with the stuff we like to use. A/C, stereo systems and the normal stuff all will load the electrical system. Like suggested earlier, grounding is important. Rust and dirt that build up between the lugs and the frame will function as an insulator if the dirt and rust is allowed to fester. The heater motor could have some issues and draw more current than it did when new, as could the wiper motor. Every ground on every light should be checked, too. After 37-42 years, we can't expect all of this stuff to be like it was when it was newly assembled. Yeah, it sucks but we like our trucks, huh?

[Longhorn Man]

It is normal to have voltage drop between the battery and the fuse box. When everything draws power from the fuse box, you will have voltage drop, period.
Example my longhorn (and every other truck I've owned) will be running at 14.6 volts, but the guage says 13, then when I turn everything on, the actual output is 13.2, give or take .1, but the guage is reading closer to 10.
That amount of voltage drop is a bit extreem, but it's nothing to be too worried about either.