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post #1 of (permalink) Old 12-12-2007, 08:39 AM Thread Starter
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Question Amp meter wiring

Correct me if I am wrong. The amp meter on my 73 CJ5 is not working. It is an after market guage, and my question is shouldn't it have one wire coming from thepositive side of the battery, to one post on the meter, then the other post of the meter going to somthing like a connection on the alternator?
Thanks in advance, and I did a search and found nothing specific on amp meter or amp guage wiring.
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post #2 of (permalink) Old 12-12-2007, 11:04 AM
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The hookup you describe is close to correct. The problem is that it only will see the current coming from the alternator. To catch what's coming out of the battery and going everywhere else, you need to identify the wire doing that. It will be big, probably a 10, and come from the positive post of the battery or from the hot side of the solenoid and run to the fuse box or into the cab. It goes to the same terminal on the ammeter as the wire from the alternator.

An ammeter shows the volume of electricity going in and out of the battery, with the exception of what goes to the starter. To do that it needs to have all of the electricity flowing through it.

On mid-70s Jeeps there are two 10-gauge wires attached to the hot lug of the starter solenoid. One carries current to the fuse block and then everywhere in the Jeep. The other brings current from the alternator. Those two wires get removed and connected to one side of the ammeter. The other side of the ammeter goes to the lug on the solenoid, where the first two wires came from. tThat puts the meter in series with everything going in and out of the battery.

But that is somewhat dangerous and inconvenient because it means running two big un-fused wires through the firewall to the gauge. To avoid that there is a "remote shunt" meter. The shunt is a very low-value resistor that ges mounted next to the solenoid and is connected the same way as the regular meter. Then two small wires run from the shunt to the meter head in the cockpit. Remote shunt meters cost several times more, so they're not real common.

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post #3 of (permalink) Old 12-12-2007, 11:45 AM
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Jim Lou is correct.....and very accurate.
To add a bit....they basically did away with amp meters for safety reasons and the fact that it was not a real good indication of overall charging health.

In the old days (as Jim Lou remembers) cars had Generators (vs alternators). Voltage was not a good indication of health...so you had an amp meter to show you how much current the generator was putting out.

My advice would be to scrap the amp meter and just use a voltmeter. By knowing the reading is before you start the engine, you will be able to tell if it's charging or not.

If you really want an ampmeter, get one of the new types that uses a clamp on probe to measure the Eddy current.

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post #4 of (permalink) Old 12-12-2007, 12:31 PM Thread Starter
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OK. Thanks!
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post #5 of (permalink) Old 12-12-2007, 02:47 PM
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Actually I have both ammeter and voltmeter, and have caught more problems with the ammeter. If the system quits charging or an excessive load comes on line, the ammeter tells you immediately that the battery is being discharged. After discharging for a while the voltmeter will tell you that the system voltage is down.

But I would do without if I couldn't have a remote-shunt unit. JD is right about them being dangerous. Having two un-fused 10-gauge or larger wires running through the firewall can cause exciting fireworks.

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