Volt Meter Bouncing - Chasing an electrical issue

FastGT94 · Oct 23, 2007

I HATE electrical problems...

Volt Meter bounces all over the place (looks like it spikes high then settles back but its bouncing back and forth like 3 times a second). This is at all rpm. Headlights dim and brighten as well so I know its not just the gauge going crazy.

Replaced the voltage regulator with another one and the problem was gone for a while, then it came back but in a different RPM range. It was now only doing it from 1800-2000 rpm.

Going by a friend's advice (and I agreed with it) I took my alternator apart, put it back together with a junk case (my case is polished) and returned it to AutoZone for a warranty replacement. Took the brand new (rebuilt) alternator & voltage regulator home and installed it. Guess what? Still bouncing volt meter. Took alternator back to AutoZone (I've had bad "new" alternators before) and it passed their test so my assumption is it is good.

Finally busted out my shop manual on CD and looked up troubleshooting for the meter.
-Point F to Ground test Passed - Voltage >= battery voltage
-Point A to Pos terminal test Passed - Voltage gauge stops bouncing
-Slip ring to case Ohm resistance >200 - Not sure what they want me to test here. I know the slip rings are what the brushes ride on but there is no connection at all between those and the case.

According to the troubleshooting guide if the Point A test passes and the Point F test passes, the alternator and voltage regulator are both good and there is either a loose fuse or a problem somewhere in circuit 36 Y/W wire.

I went to 50resto.com and purchased a new 3 wire plug and the white stator wire connector (alternator side plugs) and will splice them in once they arrive. (Some of the connections looked gross so I thought it wouldn't hurt to try). Right now wiggling the connections at the alternator didn't really yield any results. I can't make this problem happen or stop other than the Point A to (+) test which is supposed to make it stop anyways.

No, my dumb ass hasn't checked for a loose fuse yet as I was dumb enough to re-locate the fuse box and I have to take the wheel well apart to get at it.

I highly doubt its a loose fuse however. Obviously if the new connections don't help the situation, the only remaining point to check after this would be either the Y/W wire from the alternator to the fuse box, or the fuse box (a loose fuse?) itself. At least according to the Ford diagnostics.

The only thing that has me confused is that I have two different voltage regulators here and each one behaves differently. One does it at idle and 1800+ RPM and the other only really acts up at 1800-2000.

Any other thoughts / suggestions?

PS I hate electrical problems

Zero_chance · Oct 23, 2007

-Slip ring to case Ohm resistance >200 - Not sure what they want me to test here. I know the slip rings are what the brushes ride on but there is no connection at all between those and the case.

I think that in fact is what theyre having you check there. To make sure there is no contact between them and the case. If they want the resistance to be greater than 200 ohms. Are you using a stock gauge or aftermarket?

FastGT94 · Oct 23, 2007

Stock voltage gauge. No other gauges bounce. Headlights are flickering with the gauge fluctuation so I'm pretty sure its not an issue with the gauge.

Zero_chance · Oct 23, 2007

Have you put a voltmeter to any of the circuits and just verified that the voltage is actually spiking? Or are the headlights really that noticeable? Hows your belt tensioner?

BlownFiveLiter · Oct 23, 2007

Anything awfully dusty under the hood with black dust? Any particularly shiny spots on any pulleys, and they all turn freely? Your belt could be slipping somewhere. This is going along with the above mention of the belt tensioner, as I think we're both thinking along the same lines here.

FastGT94 · Oct 23, 2007

Belt and tensioner are more than tight. No belt dust either.

I have an analog volt meter (unfortunately) and it doesn't show anything spiking, but the headlights definitely dim and brighten with the voltage gauge movements.

FastGT94 · Oct 23, 2007

Also I should add that the gauge flickers whether the headlights are on or not. And the fluctuation I'm seeing is a spike when it bounces (bounces to the right, spikes and bounces back to normal) which is also why I don't think its a fuse (wouldn't a bad fuse cause a drop in voltage?)

HISSIN50 · Oct 23, 2007

Do go over your fuses. There is a fuse on the sense wire as I recall. That's what's in the underhood fusebox.

Also check the PDC connection (where the alt charge cable connects to the side of the underhood fusebox). This connection corrodes and this can cause the regulator to constantly oscillate its output because it cannot synch-up the output to the perceived battery voltage.

Give the fusible links a quick once over. I highly recommend using a new cable anyhow - I went from dropping 400 mV to 5 mV with a 4 gauge cable (and ANL fuse).

Lastly, you can temporarily rewire your regulator for diagnostics if you want. You need to ENSURE your charge cable is in impeccable shape before doing this.

Splice into the sense-wire and loop it to the charge stud. You've just removed the remote-voltage sensing function (and this is why your charge cable needs to be impeccable). You can also just loop the stator wire from the regulator to the solo-port on the case. If the alt goes back to normal, you have narrowed down which wires are the issue.

Good luck.

FastGT94 · Oct 23, 2007

Thanks HISSIN

Regarding the wire looping/splicing. Aren't the Point A and Point F tests doing exactly that? I know the point F test is a test to see if the voltage output is greater than or equal to the battery and the point A test is taking point A and jumping it to the positive battery post. Following the diagnostic how to in the ford shop manual this led me to the step where they say either the fuses or the Y/W circuit (I believe it is circuit 36) have gone bad.

It seemed that the point F test is overriding the regulator, but I could be wrong. Point A & F are the two brush screws on the voltage regulator.

I was also confused by what you referred to here "You can also just loop the stator wire from the regulator to the solo-port on the case".

The stator wire is already connected to the solo port so what looping are you referring to?

Also, I should note that the battery is (and has been for several years) in the trunk. The underhood fuse box was relocated to the drivers fender (several years ago) and the connection to the fuse box is shiny and new.

Thanks!

HISSIN50 · Oct 23, 2007

Dale, doing the remote-sense wire loop removes the Y/W circuit for all intents and purposes. I have seen one instance where the Alt fuse actually had an issue. The fuse blades/contacts were dirty and once cleaned, the issue (fluctuating voltage) abated.

The stator loop just shortens the OEM loop. You can make the loop about 5" long or less, which removes all the OEM wiring. As you saw, the wires under the loom can vulcanize badly - this can cause myriad issues. I actually had to 'chip' the loom apart, revealing vulcanized insulation and bare wires all nearly touching! Once I peeled it back near the ECT, the wires were less baked so I spliced new wires from there.

The looping method is how I would do it if I did it again. There are HD dedicated 3G regulator connectors that are made just for this (common for show-car engine bays or hot rod retrofits).

The splicing idea was just thrown out in case you wanted to make a couple of splices to see if the issue changed or got better. It sounded like doing it with the sense-wire (A terminal on your regulator) could fix an issue............

Good luck Dale.

FastGT94 · Oct 23, 2007

Thanks. I think I agree with you seeing as taking that remote sense wire out of the picture clears up the fluctuation issue...

Anyways

ReTested with a new digital volt meter here are my findings step by step through Ford’s Diagnostic check Pinpoint Test E: Indicator Lamp Flickers / Intermittent

E1.) All Connections clean and tight at alternator & battery cables?
YES – Go To E2

E2.) Check for Field Circuit Drain
Turn ignition switch to Off position. Measure voltage at test point ‘F’ on the generator regulator.

Is voltage at test point ‘F’ equal to battery voltage? YES (~12.73-12.74v)– Go To E3

E3.) Check for a loose ‘A’ circuit fuse – (The A circuit senses the battery voltage and determines generator output)
Start engine – Check generator fuse in the power distribution box for a loose connection by wiggling the fuse with the engine running.

Does the indicator lamp flicker? (Didn’t have a chance to check this yet.)
YES – Service loose fuse connection
NO – Go to E4

E4.) Check ‘A’ Circuit Connections
With engine running, connect test point ‘A’ on generator regulator to positive (+) battery post by using a jumper wire

Does Indicator lamp flicker?
YES – Replace generator regulator. If concern still exists replace generator
NO – Service poor connection in Circuit 36 (Y/W)

Until I have the time to check the fuse the only other thing I have to go by is this diagram for Circuit 36
View attachment 353709

So here is where I stop until I have time to do this right and inspect the fuse. (Fingers crossed)

Thanks for your help so far.

HISSIN50 · Oct 23, 2007

We're on the same page - I dont use a Service manual flow chart but I like to think that much of what I post is on the same page as the manual.

Circuit 36 is just that simple. All it does is note the voltage drop at the PDC vs what the alt is putting out. Then it kicks-up the output up to accomodate the drop.

Good luck with it.

FastGT94 · Oct 23, 2007

Thanks for the confirmation, I'll post back my findings in the next few days

FastGT94 · Oct 28, 2007

FIXED!!!

But I don't know what it was. Wiring was ok but I re-did the harness anyways and the fuse was still good but a tiny bit coroded so I replaced it.

So between the fuse and re-doing the wiring, (fingers crossed), so far the problem is gone. Hopefully for good.

Thanks a bunch for helping out! I personally thought it was going to turn out to be a bum alternator after doing all this work but the darn thing stopped bouncing! Weird...

HISSIN50 · Oct 28, 2007

Nice work Dale. The sense circuit is very sensitive - I have the feeling that could have been it. It will cause an oscillating meter as the regulator craps its pants trying to adjust.

Yellow302 · Apr 12, 2013

4-12-2013

Just adding my similar issue.
I had oil driping into my alternator (relocated for the supercharger)
Fixed the oil leak.
Installed new altenator.
Removed drivers side ground wire. Found it to be loose.
Reinstalled ground wire on the back of the altenator hosing and connected it to the sway bar bolt.

So far so good, car runs stronger as well.
I will add another ground wire from the engine to the drive side sway bar bolt.

Kevin Silva · May 17, 2015

New to this site but read over all the comments and I'm having the same problem. Except it only happens when I put my windows up.. Lights dim and then go back to regular.

Video: View: https://www.youtube.com/watch?v=6IZFFlqWFKc

If anyone can help that'd be great!

Thanks in advanced.

HISSIN50 · May 17, 2015

Kevin Silva said:
New to this site but read over all the comments and I'm having the same problem. Except it only happens when I put my windows up.. Lights dim and then go back to regular.

Video: View: https://www.youtube.com/watch?v=6IZFFlqWFKc

If anyone can help that'd be great!

Thanks in advanced.

What's the clicking noise?
Are your windows going up and down or is there an issue with the window movement?

Kevin Silva · May 17, 2015

The clicking noise is me pushing the window button up, The window works and everything but it seems to happen every time I put the windows up and someones when idle.

Adding to this, Every time I turn the car on it beeps for 4 minutes like you hear in the video. Not sure if every 94 Mustang does that.

HISSIN50 · May 18, 2015

Kevin Silva said:
The clicking noise is me pushing the window button up, The window works and everything but it seems to happen every time I put the windows up and someones when idle.

Adding to this, Every time I turn the car on it beeps for 4 minutes like you hear in the video. Not sure if every 94 Mustang does that.

If you're continuously pressing and depressing the window button and the meter fluctuates at the same time, that's not uncommon. The meter normally dips when the button is depressed and it readjusts when you release the button (the PW is a relatively large load). Even a turn signal (the same sort of recursive load cycle) can cause a meter to fluctuate.

I'm rusty - one of the other guys can chime in, but the beeping could be from the airbag. I seem to recall a redundancy that it will beep (esp if the airbag warning light is inoperative) if there's an issue with the system.

Volt Meter Bouncing - Chasing an electrical issue

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