[Hotrodjohn71]

Hi group, my 1967 Firebird never came with an ammeter and I'm thinking about installing one. I found on another group an idea that a guy had for the wiring of the ammeter but he never got any feedback. What do you think of hooking up an ammeter according to this drawing? Thank you

[Bill Hanlon]

The picture is too fuzzy to tell for sure, but I'm betting it wouldn't work. 1st reason? You have to cut the main power feed where ever you install an ammeter and there is no info about cutting in the diagram you posted.

[steve25]

Basically Amp meters have to be in series with the big hot red lead off of the rear of the Alt.

But that being said I think your diagram will work as that’s call the shunt method of reading current,

[steve25]

I do not think that will work, as I just found a diagram for a 1964 and yes one wire goes to the relay, but the other goes to the ignition switch, the terminal marked ING #1 SPL,

[Hotrodjohn71]

Thank you Steve. That makes sense. The wiring in the drawing would probably have the ammeter working all the time even when key switch is off.

[lust4speed]

Ammeters fell out of use when alternators grew in size. Think the last use of an ammeter in a Pontiac was maybe 60 amp? A 100+ amp alternator would do nasty things to the gage during maximum charging. We bypassed the ammeter in our '65 big cars because they couldn't handle the current of the upgraded alternators.

The posted diagram doesn't make any sense and definitely not measuring amperage as drawn.

[punkin]

That's one of my concerns as well unless a shut circuit is used. More to your point, as the modern alternators got bigger, a lot of folks forget about the charge cable size too.

[dataway]

I've noticed on various old cars and tractors a lot of burnt up amp meters and amp meter wiring. I remember going to install an aftermarket unit many years ago that required running the alternator output line to the meter inside the car ... no way I was going to do that.

A shunt on the negative battery cable with a sensing wire switched by the ignition would probably be the safest way. Although that would not directly indication alternator output, it would show if the battery was being discharged during times of high load, and when it was being charged.

Another option is just a volt meter, it won't show you alternator power output, but will show alternator voltage output. Volts over about 15 vdc might indicate over charging, volts under 12.5 vdc would point to battery discharge. The wiring for a volt meter is very easy and safe. Heck, if you had an old school voltage regulator you could meter it on both sides and get a good indication of alternator and voltage regulator health.

[Hotrodjohn71]

This makes alot of sense. I think I'll use a volt meter instead.

[JC455]

Back in my teens, my buddy had a 64 Chevy II Nova that we took a trip in(We were taking it because my 455 T/A liked gas much more than his 194 6 cyl- lol) to see some friends.
Well, we thought we were... we had no sooner left my driveway and got up to a whole 20 MPH when the car died/cabin filled with smoke/he stopped the car as we both bailed out!!
Amp meter wiring must have chaffed, but it shorted and burned that harness badly!
I was able to patch it together, but that set a standard for me at a young age: Voltage Meters Only!

[lust4speed]

A remote shunt will work, but would need to go in the minor circuit between battery and the harness going to inside of car. It would measure current on everything except starter since the negative battery cable sees excessive current during starting. A properly sized shunt will handle and report actual loads to the ammeter, but if the ammeter isn't designed for the greater charging ability under full draw it would still peg and possibly damage the gauge. Later GM systems used 4 amp fuses on both small wires from the shunt to the ammeter and they would probably blow since the ammeter sees a percentage of the current and would still be pushed beyond its operating range with a high capacity alternator.

[shermanator2]

Your notes on the diagram make little sense. If you want to put an ammeter in you would need to break the connection somewhere near the "Junction Block" in that picture and put the ammeter in series there. Last time I looked all of the aftermarket automotive ammeters that I could find required full current through the ammeter, This means running a pair of fat wires from somewhere near that junction block to the actual meter. This is pretty scary because you end up with full battery power on a couple of screw lugs behind the meter. I still have a scar on my arm from when I was about 20 years old (long long ago) and got a metal watch band from one of those to ground. Melted the watch band which I was much more upset about than the burn on my arm.

Ammeters should be set up with an external shunt, but I have not been able to find one in the automotive aftermarket made that way. Here is one from the marine world that I really like: https://www.bluesea.com/products/173...meter_-_Yellow I have used this one in my chevy truck where the clock used to be and have another one to go into my GTO when it goes back together. This one has an external shunt that gets mounted right next to the Junction Block. Then small fused wires are run into the interior to the meter. The shunt is exposed so that you need to make an insulating cover for it, but otherwise an easy install. The only real problem is that it is not the right size or look for a car. It it too small to fit in a gauge panel and certainly does not look like it belongs in a classic car. I think that it is made to go into the same bore as a cigarette lighter if you want to put it there.

I agree with what others say about a volt meter being appropriate these days. They tell you different things, but either will tell you if your charging system is working. I think that the reason manufactures switched to volt meters was not because charge currents got larger, but because the masses understood volts more than amps, or at least they thought the did. I am an electrical engineer, so I like to have both.

["QUICK-SILVER"]

Originally Posted by Hotrodjohn71

What do you think of hooking up an ammeter according to this drawing?

Look close at that drawing!

A full flow ammeter, wired as shown, would by-pass field wire switching in the voltage regulator. Field wire switching is how the regulator controls alternator output.

Get some one to double check this... But pretty sure hooking battery volts directly to field/blue would make the alternator charge WIDE OPEN out of control.

Clay

[george kujanski]

An ammeter should only be of the shunt type, the traditional style would require connecting large wires to the meter on the dash. Not recommended in today's cars.

A voltmeter is better...still gives an indication of charging and only requires small wiring to connect. All modern cars use voltmeters. That's what I would use.

George

[shermanator2]

Originally Posted by "QUICK-SILVER"

Look close at that drawing!

Get some one to double check this... But pretty sure hooking battery volts directly to field/blue would make the alternator charge WIDE OPEN out of control.

That is true and exactly how I interpreted his sketch.