Voltage gauge reading question.

[bronconut73]

My Autometer volt gauge is sitting at 12 volts with the engine running. When I turn on electric fans, wipers, etc...it dips a little near 11 volts.
Never worried too much about it because while using my volt meter on the battery I noticed that while running it is at 14.4 volts. Alternator is working quite well.

Shouldn't my Autometer volt gauge reflect that 14.4 volts noted at the battery with the engine running?

 

[gr8scott]

Yes it should. Make sure it has a nice clean ground. Where are you pulling its + power from?

 

[Broncobowsher]

Put the meter on the back of the gauge. If the meter matches the gauge, you have wiring issues. If they don't match, you have a bad gauge.

 

[bmc69]

That's a large loss. Better find out where and why. I watched the voltmeter on my '89 F-250 drop over the period of a year or so..and finally the culprit emerged; the fusible link power supply wire flamed out and left me sitting by the side of the road.

If you are losing even half a volt between battery and the consumers the gauge shares power with, your line losses are too high and somebody going to get hot somewhere.

 

[bmc69]

Put the meter on the back of the gauge. If the meter matches the gauge, you have wiring issues. If they don't match, you have a bad gauge.

Ha. A good check...

 

[bronconut73]

Best place to supply power to the volt gauge from?

I need to climb under there and do what Bowsher said anyway. Its been quite a few years...I think I sent power to it from the ignition switch....

 

[bmc69]

Best place to supply power to the volt gauge from?

I need to climb under there and do what Bowsher said anyway. Its been quite a few years...I think I sent power to it from the ignition switch....

Switched power from ignition switch is a good source. Lets you see what the various "consumers" are seeing and that's what really matters.

 

[bronconut73]

So.....I was under the dash doing something and I thought hey....while I am here lets put the volt/ohm meter on the ignition switch 12 volt supply that I powered my volt meter with.
It reads 11.97 volts. But as before out at the battery I get 14.2 so the alternator is doing fine.
Interior nor headlights ever dim when fans or other accessories are turned on, so with that and my 14.2 volt readings I figure my alternator (3G) is doing great.
But only 11.9 volts at the ignition switch.
How do I get that 14.2 at the battery to show up on my Autometer volt meter (?) without it being straight wired to the battery which would not be right either.

 

[Marshall]

Sounds like you have typical voltage loss in the wiring, nothing to worry about. For example, if you notice your service to your house breaker box is 2-120 volt lines, but everything (all typical receptacle, not including the 220 stuff like stove heat pump, water heaters, etc) in your house that plugs in (tv's etc) only need 110 volts, so they say 110 VAC, even though the power company is supposed to deliver 120 vac to your breaker box. Similar for cars, 14 VDC at battery, then some voltage drop loss in wires and across components, so like someone said you are getting a decent idea of what your lights and radio, etc are actually seeing. If it gets too low it would be a problem, but as long as it's close to 12vdc, you are fine. If it continues to drop, obviously it could be a ground, or the alternator isn't doing its job.

 

[Steve83]

High resistance somewhere between the battery & the ignition switch.

When no current is flowing, the "static" voltage at the ig.sw. will be the same as the battery. But as current increases, the resistance will cause more voltage drop; like a kink in a garden hose - lots of pressure when you block the end with your thumb, but just a trickle when you try to blast it. Voltage is analogous to pressure; flow is the same as current (whether electrons or molecules). So if you hotwire the ignition (literally) from the battery, and unplug the ignition switch with the engine running, you'd probably find 14.4V at the ig.sw. feed wire.

But just start moving the DMM probes (ONE at a time) along the ig.sw. feed wire and any ground SLOWLY (small steps) toward the battery. When you move a probe, and the voltage rises, you just crossed some resistance. Move half of the last step back toward the ig.sw. to pinpoint the resistance. When you find it, clean the mating surfaces (connector terminals, or ground wire, or rusty body panels...) or overlay a new jumper wire across the problem.


AC voltage is an entirely different animal, and there are MANY reasons why you see ratings from 105VAC to 130VAC for US household power & appliances. It's not resistance or poor connections or voltage drop; it's the nature of AC power production & distribution that there are regional & momentary variations.

 

[bronconut73]

I will get on it in the morning.
Thanks fellers!

 

[DirtDonk]

Stock wiring on the rest of the vehicle (other than the alternator) bronconut? If so, with the battery disconnected pull the connector behind the ammeter gauge in the dash apart and check for corrosion or a loose fit.

I disagree with you on this one Marshall. Yes it's common to lose a volt at the dash on an old Bronco wiring setup. But losing roughly 2.3 volts at the ignition switch is very bad juju. It's basically a big loss early in the system that can very easily turn out to be even bigger after the switch.
Heck, that large of a loss might be even more common nowadays! But it's still very bad and should be fixed. In my opinion anything more than a half-a-volt loss at the ignition switches Yellow wire is worthy of tracking down.

Basically bronconut, the large Black wire from the starter relay is where that power comes into the cabin, then throughout the system and back out to the engine compartment. Where you supposedly have it disconnected from the alternator now that you have a 3G swapped in?
The starter relay with the fusible link is the other end of that wire, as you know. But it's also where everything else gets their power feeds from. The Yellow wire that feeds the ignition switch is not a very large gauge wire, but it's a relatively short run to it's splice into the Black wire.
Another place to check when you get the chance would be the headlight switch power feed. I believe it's a Black w/orange stripe wire at the headlamp switch. If it's got full battery voltage, then the fault lies somewhere between the splice and the ignition switch along it's Yellow wire.
If the voltage at the headlight switch is as low as you've read at the ignition switch, then the Black and Black w/yellow wire has a loss somewhere.

I'm hoping for the big connector at the ammeter. It's the easiest to deal with!

Good luck.

Paul

 

[Marshall]

It's ok to disagree, but I'm qualified, I stayed at a holiday inn last night.

Actually I'm an electrical engineer, and I do this stuff all the time, frankly it's the only thing I know, but hey, I've been wrong a time or two.

 

[DirtDonk]

Me too! And probably wrong a lot more often than most I bet.
'Cause it's been awhile since I stayed at a Holiday Inn.%)

I don't disagree that a little is normal and, even if not optimal, is at least acceptable.
But that much of a loss so early in the system, and at the source for so many other loads (ignition switch supply), is definitely worth taking the time to track down the reasons for. And fix if possible.
Old age is a good reason (I use that excuse all the time in fact) but not a good reason to leave it alone I don't think.
Broncos need as much love as they can get when it comes to electrical stuff already. Especially in the grounding department, as you mentioned.

Maybe that level of loss is not showing it's ready for a meltdown, but it pays to be safe I think. And it's certainly losing efficiency in a great many other components I would think. Everything from the ignition system (with an additional resistor that would reduce the voltage to the coil even more), to the heater motor, to turn signals to whatever.
And if it's the main Black wire causing the loss, then literally everything is losing out. Headlights that are dim enough when it's all working correctly and all.
For comparison, when my stock '71 system was a lot newer (like 40 years ago, give or take), I would get less than half a volt loss at the ignition switch's Yellow wire.

So not doubting your learnin' at all. Just thinking that with that much loss it's time to start playing Sherlock Holmes and find the culprits.
If only for brighter headlights and a hotter spark, it would be worth the time and trouble.

Paul

 

[bronconut73]

Got it.

When I hooked up my Autometer gauges I used the power source for the heat/defrost lighted display for my
Autometer gauges lights. Volt meter was one of the last ones I installed. When I did I accidentally used the light power source for the sensor wire of the volt gauge.
Power feed I made from the ignition switch was still there with an open butt connector ready to hook up, lol....

Now have 14 volts on the gauge.


Thanks guys. I would have bet a dollar I hooked it up right initially since I made that feed wire off the ignition switch.
Getting old I guess...lol,,

 

[DirtDonk]

Glad you got that one fixed. Now you can sleep easy knowing what's going on at the alternator/battery side of things.
Still low reading at the ignition switch, but that's a project for another day maybe.

Paul

 

[bronconut73]

No Sir.

Ignition switch voltage is 14. The wire supplying the sensor on the voltage gauge is the wire off the ignition switch. All is good there.
The wire that was mistakenly feeding the volt gauge sensor was the light power supply for the defroster/heater lights. That wire is now only supplying power to the gauge lights as it should.

 

[bronconut73]

I just noticed that with every accessory on

A/C and fan on high
Tranny cooler fan on
Engine cooling aux. fan on
Headlights on
Wipers on high
Stereo on
Etc...
Volt gauge goes from about 14.2 to 13.2 at idle with that load.

That's pretty good. All of my accessories pull quite a load. That 3G must be doing fine.

Thank you all.

I really love this site.
I can't remember what I used to do before CB but my progress with all you fellers helping is so much faster.

Many thanks gentleman.

 

[DirtDonk]

That's great news! I was just going back to the one post where you said you checked the back of the ignition switch while you were under there and were getting low volts there too.
I might have misinterpreted what you were saying then.

Glad you got it sorted.

Paul

 

[bronconut73]

That's great news! I was just going back to the one post where you said you checked the back of the ignition switch while you were under there and were getting low volts there too.
I might have misinterpreted what you were saying then.

Glad you got it sorted.

Paul

Well....I misrepresented that Paul. I went to a wire that I was sure was hooked to the ignition switch.
My,mistake....it was that wire that was for the light source that I had accidently used as the volt gauge sensing wire.

My ignition switch is tough to get to now with my gauges right there, lol.