Ammeter NEVER shows discharge

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str12-340

str12-340

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1970 Dart. Long ago after seeing all the horror stories I installed an aftermarket ammeter below the dash, hooked the wires from the ammeter in the cluster to it and everything has been fine for 20 years. I had the system overcharge, as shown on ammeter and voltage gauges (regulator went haywire), and it melted connections in the bulkhead connector. I installed new terminals in a new bulkhead connector, and replaced any damaged wire (very little). Now the ammeter works fine and the electrical system seems to work fine, but with one small issue: when you start the car the ammeter shows charge and slowly comes down, but the ammeter NEVER shows a discharge. You can turn on the ignition, without starting the engine, pull on the high beams, turn on every accessory and no discharge indication. I thought I toasted the aftermarket ammeter, but tried two others and get the same result.

Suggestions???
 
str12-340 said:
1970 Dart. Long ago after seeing all the horror stories I installed an aftermarket ammeter below the dash, hooked the wires from the ammeter in the cluster to it and everything has been fine for 20 years. I had the system overcharge, as shown on ammeter and voltage gauges (regulator went haywire), and it melted connections in the bulkhead connector. I installed new terminals in a new bulkhead connector, and replaced any damaged wire (very little). Now the ammeter works fine and the electrical system seems to work fine, but with one small issue: when you start the car the ammeter shows charge and slowly comes down, but the ammeter NEVER shows a discharge. You can turn on the ignition, without starting the engine, pull on the high beams, turn on every accessory and no discharge indication. I thought I toasted the aftermarket ammeter, but tried two others and get the same result.

Suggestions???
Click to expand...
I think it depends on how you have wired the aftermarket ammeter. It sounds like the charging current from the alternator to the battery is going through the ammeter but the discharging current from the battery to the lights, ignition and accessories is not. There is no way to tell without knowing how everything involved is wired.
 
I just took the wires off the studs on the stock gauge cluster and put them on the aftermarket gauge
 
The factory ammeter measures all current flow in & out of the battery w/ a few exceptions. It doesn't measure transient under-hood loads - starter, horn, nor factory in-cabin options like spotlight or (I think) convertible top motor. Also, it wouldn't measure an add-on stereo which tapped the big BAT wire (red) before the ammeter.

Thus, as you wired it the same, you should see discharge w/ the headlamps on high-beam, but it won't be much say 5 A on a ~100 A scale, so you might have to look close to see the needle budge. Try actuating the brake lights at the same time. I have a neat clamp-on DC ammeter for easily measuring currents in various wires.
 
Bill, thanks for responding, but really this ammeter NEVER shows ANY discharge. I hooked up 2 other aftermarket ammeters that I had sitting around and still it doesn't budge on the discharge side, but shows typical reaction when you start the car with a big charge slowly coming down to just a continuous small charge as you drive it around. Go Figure...
 
Perhaps a prior owner did the "MAD Bypass" under the hood. Disconnect the "BAT" wire (usually thick red) from your ammeter and measure the resistance between BAT+ terminal and ALT+ (big stud). If <100 ohm, there must be a parallel path to the battery around the ammeter. If so, you might not see a discharge current, but would still measure the much larger charging current after starting.
 
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