How were Police Amperes gauge wired?

[87gtVIC]

Out of curiosity?

[gadget73]

Normally the alternator charge cable passes through it. Kind of stupid, I don't want wires heavy enough to carry 130 amps running through my dash, nor do I want to risk having a gauge fail and kill my charging system. A voltmeter is a better idea. It will tell you just as much without the fat cables. I think Scott *may* have one up there, though not sure if it matches the gauge set you have.

[jayh]

x2 on voltmeter

[87gtVIC]

I am not planning to use it. I was just wondering because some police cars had them installed and it would be a hell of a job to run the charge cables into the car and just right back out to the engine bay again. I was wondering if there was some dummy way they did it sorta like the idiot amp light.

I know my dads mustang has an amp gauge. I am going to look at his EVTM and see how that is wired up.

[87gtVIC]

okay I appear to have found my answer into safely installing an AMP gauge into a vehicle. There appears to be something called a SHUNT wire that must take the brunt of the electrical burden allowing the other wire to take a safe reading. Can anyone explain this further even if it is just pure speculation?

This was printed on the back of my amp gauge:



And I found a similar phrasing in my dads 1985 Mustang/Capri EVTM:



Ideas, comments?

[gadget73]

Ah, its the remote shunt type. Most of the aftermarket gauges I'm used to seeing have the shunt built into the gauge. That makes a hell of a lot more sense. Basically at that point, its a voltmeter and using a bit of ohm's law magic, you get the amperage by measuring the voltage drop across a known resistance, which is what the shunt is. Probably its a 1 ohm resistor or something small to provide minimal voltage drop, but enough for the gauge to read.

[87gtVIC]

Interesting.

[trwp72]

And those amp gauges rarely, if ever work! I have had amp guages in ALL of my older Plymouth police vehicles, and the only time they even moved was when you turned on the headlights, they would "jump" and then go right back to the center. They never showed discharge, even if you disconnected the alternator... Volt gauges are much better, as they tell you how much juice is in the battery... if you look and it says below 12 volts, you have a problem! Most emergency vehicles have gone to volt gauges...

[87gtVIC]

That could also mean that the voltage regulator was doing its job.

[ÆJackacks]

ammeters are what caused my bro's stang and my continental to all of a sudden stop working and almost catch fire,

Here's a nice little history of ammeters in ford cars http://automotivemileposts.com/garage/v2n7.html

"A shunt wire in the circuit allowed only a small amount of electrical power to flow through the gauge itself, which meant the needle didn't move very much. Only very strong charging or discharging would cause the needle to move, and even then the movement was so slight most people didn't notice it."

[trwp72]

that could also mean that the voltage regulator was doing its job.

The alternator went out once on my 73 Dodge Polara, and once on my 78 Fury... The Gauges never moved towards discharge... which it is supposed to do to show that something is not right with the charging system... nor did they go above zero, when the alternator was replaced, and it started re charging the battery...

[gadget73]

I think Chrysler put the ammeter between the alternator and battery, so if the alt stopped, you saw nothing. If the battery was really low, you might see it swing over to the C range, but they usually didn't do very much.

[87gtVIC]

The one in my dads mustang rarely moves.

I have an amp gauge just sitting in an a pillar gauge pod in my car atm. I guess if it really wouldn't move at all then it would look as if it is already hooked up so I will just leave it. Anyone asks...I will just say the car is charging fine and there is nothing to worry about.