Voltage meter oscillates with rhythm of turn signal...uh, WTF?

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Oct 18, 2009
Paso Robles, CA
So I was waiting to turn left at a light when I noticed my voltage meter was oscillating between about 9 and 12V in a very distinct pattern. It took me a couple of minutes to realize it was mimicking the rhythm of the turn signal. Has this happened to anyone else? Does it really mean anything?
Guessing a bad ground.
If you've owned your rig for a while and this is the first you've noticed it - could be a bad bulb. Does it do it on right turns also? Also moisture in a light fixture might be causing a short to ground.
It is pretty normal and it indicates that your alternator isn't putting out enough power to keep up with the total demand with the turn signals on. No doubt if you rev it up it will go away.
On my 60 it turned out to be a bad flasher. Did EXACTLY what you are talking about.
Only during idle and with the left turn blinker going, from what I noticed. Changed the DS corner running light bulb last week, but that's it.
Yep, mine does this as well. I'd say it is fairly common if you're running a stock alternator that may be a few years old. Both my battery and alternator got me through several sub-zero Missouri nights last winter so I don't worry about it too much. I don't use mine as my DD however. :cheers:
Mine has done that since last October and then finally the alt took a dump
Pretty common.

Annoying, but "normal", especially on a 91-92.

If no other symptoms are present, just live with it; even replacing the alt. isn't a guaranteed fix.

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My 92 currently does it. Doesn't matter if it's the left or right turn signal. No biggie though... I can live with it.
My 94 does it but it is very hard to notice unless you really look hard at the needle.
My alternator is only 2-3 years old.
Not a big deal in my book unless it is really moving up and down like crazy.
A bigger battery will reduce/eliminate it. Happened on both mine and the :princess: truck. Went away when I swapped my batter to the Sears PM-1.

If it's relatively small movements, then I'd say normal. If it's huge swings, then you have a problem (bad ground, bad battery, alt going out, etc).
Only during idle and with the left turn blinker going, from what I noticed. Changed the DS corner running light bulb last week, but that's it.

I would check out your left side turn signal bulbs, (both front & rear) housings and wiring for damage, corrosion or shorts.
I've experienced the same problem when running an after market alternator, after it died I went back to one from Toyota and still noticed some fluctuation while at a light waiting to turn at low idle. As long as you're getting a good reading that your alternator is charging at consistent speeds and with Lights, A/C, stereo all going you should be ok.
Mine does this as well, and in addition, the tach will follow the pattern, as the alternator engages and disengages. ebag's suggestion of a bigger battery makes sense to me, and it makes for a good excuse to upgrade!:bounce:
Suggestions for battery upgrades?
sorry for my bad english my hj60 have the same issue, but its rare because when the niddle of the voltage ocsillates the fuel niddle ocsillates too, its very annoying, i tried to replace ignition relays, blinkers, including the battery and it persists, im geeting crazy for it, so the unique clonclusion i get is the alternator, maybe the relay of the alternator or a bad ground, i tried doing only ignition with out starting the engine and it ocsillates if i started the engine have the same issue... so.. HELP!! haha

I have not noticed the oscillation on the dash, but I do have a digital voltmeter in the cig lighter outlet and there is a significant fluctuation when the turn signals are on. Not surprising.
Its the load of the filament bulbs, analog flasher, putting a load on the system. I went to an electronic flasher and it almost disappeared. I am slowly switching from filament bulbs to LED. This will significantly reduce load but it will always be there just not as noticeable. Check grounds as everyone suggested and test alternator.

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