1966 Ammeter shunt wiring. Too much shunt ?

[Alberta Magpie]

Hello all
I'm looking for info on my shunt wire for my ammeter gauge.
The block is mounted near the battery on inner fender.
The gauge works but barley moves.
Battery reads 13 -14 volts charging with a volt meter after leaving lights on then starting car.
Gauge moves slightly to charge side.
If I turn lights on with engine off needle moves to discharge, but only slightly.
Everything seems to work OK but gauge barley moves chrg/dis chrg. No it's not stuck.
I'm looking for info/pics on the proper wire gauge for the actual shunt wire.
Yah I know somebody thought it would be cool to paint everything black.
The shop manual doesn't seem to indicate a detailed enough picture.
To me that wire is more of a huge fuseable link.
Any thoughts would be helpful.
Thx all

[DakotaLee]

Looks like a good junction block to me, under that paint might be the date code on the wire, looks original, pretty rare to see if so. I wouldn't touch it if it's reading properly on a multimeter.

[Alberta Magpie]

I see your point (if it ain't broke ...) but I'm talking about the needle only moving less than 1/8th of an inch either way.
I'm not looking for exact current numbers ,just something with a little more needle swing when chrg/drain is 5,10,15 amps or so.
I just wish this drawing showed the shunt wiring/cable details better.
BTW the regulator has been replaced in the past. Nice and shiny. I know it should be black.

[georgemii]

Rather than a “fusible link”, you might think of the shunt as a “calibrated resistor”. It introduces a known voltage drop, which is displayed as “amps”. Very unusual- although certainly possible- that the electrical values have changed.

Is this a new symptom/change? How does the ammeter behave when headlights are switched bright/dim? How does the ammeter behave when brake lights are applied?

FWIW - my (‘65), which I know is accurate, behaves the same way. Hope this helps.

[Alberta Magpie]

So after some sleuthing I'm back to my original thoughts.
Lots of comments/info found after searching "junction block" on this forum.
The junction block is indeed a fusible link for assorted vehicle power.
So where my "ammeter shunt wire" location/value is, still remains the burning question.
To me it seems like whatever value shunt (ohms) being used now has incorrect resistance.
I do not know how much current draw would be required to give a max needle deflection. Again...not looking for exact numbers ,just for comparison
as in headlights should move needle waaay more than a map light.
As a result I am not seeing a full scale deflection (F.S.D.) for a presumed value of 20 or so amps in either direction. Chrg or Drain.
Now one could utilize a fusible link as a shunt also. Two for one. But a shunt wires properties (impedance)are usually much more stringent.
Then again ,we aren't in a spaceship!
OK I'll stop now. Been up since 5am guzzling too much coffee.

Besides telling me to stop talking any more info would be appreciated.

Squawking like a Magpie.

[Alberta Magpie]

Thanks George


I posted my last comment before seeing your post.
Gauge has behaved this way since I purchased the car,5 yrs.
Meter barely moves 1/8 inch with headlights all on (4) , even with engine off. Brakes the same.
As for a 3 inch long 12 gauge wire used as a shunt the effective resistance would be pretty much zero.
Even though shunt values are normally very close to zero in most cases.
The issue is if the junction block is serving double duty as a fusible link and a shunt.
Or is it just a remote shunt. Located on the fender as opposed to under the dash for fire safety.
In that case one would also include the cable resistance of the wire running from the gauge to the junction block
I'm gonna pull the gauge and calculate the FSD current and internal resistance for the ammeter.
Then measure back the resistance through the wiring whilst attempting to dis-connect assorted branch wiring.
I'll base this on 15 volts and see what shunt values I come up with for a theoretical current draws of 25 to 40 or amps max.

I'll shunt-up now
Thanks all

Got myself some homework now.

Alberta Magpie

[georgemii]

01. I believe - someone here, please correct me -
that MY ‘64 and ‘65 utilized ammeters with
internal shunts. I understand that the higher
current was hard on harness/connectors so
Ford changed to external shunt in MY ‘66,

02. I don’t know where the shunt is located, or
it’s configuration. (Mine is a MY ‘65.)

03. Yes, the shunt will be very low impedance.
Not a spaceship, but just for reference, shunts
in current aircraft are 50 millivolt for FSD.

04. Which does not tell us what Ford did .?.?.

[cacockrum]

My limited understanding is that '64 and '65 Birds routed the entire charging current through the ammeter, and as the cars aged some of the connections (especially at the firewall feedthrough) developed a high resistance which got hot enough to create a fire. To eliminate this problem, in '66 the ammeter was replaced (I believe) with a volt meter, the inputs to which are connected to either end of the shunt wiring. If this is correct, the high internal resistance of a volt meter would limit the current flow in the shunt wiring to a small value such that there would be little difference in the voltage at the two terminals to the meter, and therefore very little deflection. I know that I had to look closely at the "ammeter" in both of my '66s to see any deflection, but they did indicate either something greater than zero when they were running and something less than zero when the ignition switch was on but the car was not running. When I restored my '68 I had the meter converted to a volt meter which read 12 volts +/- 3 volts, so I now get an accurate reading. If you are interested, Bob McMillen at RCC Innovations (www.rccinnovations.com) did the work on the meter, AND I had to reroute the wiring so one side of the meter was grounded and the other was connected to a switched 12 volt line.

[Alberta Magpie]

Referring to the previous post

"To eliminate this problem, in '66 the ammeter was replaced (I believe) with a volt meter, the inputs to which are connected to either end of the shunt wiring. If this is correct, the high internal resistance of a volt meter would limit the current flow in the shunt wiring to a small value such that there would be little difference in the voltage at the two terminals to the meter, and therefore very little deflection."

http://www.vintagethunderbirdclub.net/p ... 9bc079593a


What we are talking about is a series (load)/parallel (shunt/meter) circuit. Voltage is the same for both components (R2,R3).
This depends on the voltage drop across the load.
Current flow in the shunt is a product of it's own resistance (R2) and pretty much all of the load current (R1) .
Increasing the resistance value by substituting a volt meter (R3) with a higher resistance will actually slightly increase shunt current flow
(A bit of OHMS Law ).
The reason for measuring such a low value voltage wise, using a voltmeter is because you are basically measuring across an almost dead short (the shunt).
This would appear to support the theory that a voltmeter was substituted in for the ammeter resulting in very limited meter movement.
Which leads us back to:
1 Is it an Ammeter or Voltmeter ?
2 Is the "Fusible Link" a fancy name for the shunt assembly, which can also double as a fuse due to the shunt gauge #
wire being a smaller gauge # then the cable wiring gauge #.
Which consists of the Junction block wiring and cable wiring leading back to gauge together
to form part of the resistance wire (shunt) value.( in OHMS).

Magpie

[Alan H. Tast]

Through the 1964-66 and later runs into the '70s, an ammeter was provided for monitoring the electrical system. Factory installation of voltmeters in Ford products didn't really come about until the mid-late 1970s, if not the early-mid 1980s if memory serves me correctly (a voltmeter was used in 1940 Ford cars, but that was a lone exception as years prior and following used an ammeter).

Bear in mind I'm not an electrical engineer, as evidenced by my signature.

[cacockrum]

Magpie I'm curious as to why you are focused on the fusible link. My understanding of the wiring diagram (as reproduced in a smaller, hard-to-read size in Osborn's Electrical Manual) shows the two wires that go to the "ammeter" have little to do with the fusible link. Both of these wires originate at positive battery terminal of the starter solenoid. One (red wire number 655) goes directly to one terminal of the meter, and the other (yellow wire number 654) branches off of wire 37B (black with a yellow stripe) which also originates at the same starter solenoid terminal. Wire 654 goes to the other meter terminal and nowhere else. Two other wires start at the branch point where 654 originates. One is number 37 which goes to the rectified output of the alternator, and the other (number 37C) goes to the fusible link, and then continues on to the ignition and headlight switches. In addition to the positive battery cable which terminates at the positive terminal of the starter solenoid, wire 152 (yellow) goes to the voltage regulator. So there are 4 wires connected to the battery terminal of the starter solenoid, and the value of the voltage at that point will be determined by the line with the highest voltage, which, if the system is working properly, will be the combination of the alternator and regulator, or the battery if it is fully charged.

My best guess is that the internal resistance of the meter is very high (which is especially true for a volt meter) so that it draws little current when connected --- as opposed to an ammeter which has very low internal resistance and therefore introduces a very small voltage drop when it is used to measure current. In this example, the current that flows through the meter is determined by the value of the voltage at the starter solenoid and the combined resistance of the meter and two wires connected to it (I = V/R). If all of that is true and the meter is designed to read "zero" at 12.6 volts, a value more than 12.6 V will produce a positive deflection and vice-versa. Since the resistance of the two wires is at most 1 or 2 ohms, and the meter could easily be more than 1000 ohms, changing the length or gauge of the wires would have no noticeable effect.

That's my 2 cents worth. I would appreciate any comments/suggestions.
Art

[redstangbob]

Magpie, I see you joined us 5 years ago. Surely you've seen the many posts on the limited movement of the 66 ammeter. The Flairbird used an Amp gauge as opposed to the 3rd gen charge light, as you know. The 64s burned up because all electrical load was passed directly through the ammeter. In 65 the harness was improved but still had to handle full load. So in 66 things were changed, the Amp gauge had very little deflection by design. If you get a little charge showing when running, and a little drain with lights on and engine off you're good. JMO, Bob C

[Alberta Magpie]

Cacockrum,I'm not so much obsessed with the fusible link as one may certainly come to that conclusion (I would too) as my
quest to figure out why my gauge barely moves either way has bothered me for quite awhile.
Unfortunately your schematic lacks the resolution for me to clearly read when blown up.
Mine looks like cave art compared to yours. Looks like way more detail.
I thought from previous "research" that it had something to do with fire hazards because the shunt was located in the dash.
Which was moved on 66's to the fender instead.
I believe it has been mentioned in ref to 64's and 65's.
It would appear I have wandered down the garden path once again. I was wrong.
Let us forget about my malfunction at the fusible link junction and move on.
My 66 Ford shop manual pg 22-6 is what I used.
What is driving me crazy though is that little wire # 37.
If the gauge is connected across 654 and 655 via the little #37 wire then electrically they are tied together at the same point.
To me that that could/would have to be the shunt. Which would make sense to me.
The current flow direction depending charge versus drain operation.
I will leave it at that.

Sidebar
I am not trying to make make a mountain out of a molehill.
I am very familiar with the operation of meters (volt,amp,etc).
All I wanted was the challenge of figuring out why the ammeter is working the way it does.
And maybe coming up with a solution to explain why.
Thanks to all who contributed to this post.

Magpie

[stubbie]

As Bob pointed out, as posted by others the deflection of the amp meter is minuscule when in use unless you have a major problem.