Amp meter reading backwards

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Don K

Don K

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Recently picked up a 74 duster and been working out the bugs. I found it was not charging replaced the voltage regulator and fixed the problem. About 14 volts to the battery but when I looked at the amp meter in the car it is reading discharge. So before I start tearing things apart any ideas? Amp meter cross wired?
Thanks in advance.
 
The ammeter, is really a charge / discharge meter.

There are two wires on the back.

Reverse them and the meter will read correctly.

Disconnect the battery FIRST!!!!


THIS ALL ASSUMES THERE IS NOTHING ELSE MESSED UP WITH THE WIRING.
 
You can change the wires going into the bulkhead in the engine compartment. A bit easier then climbing under the dash.
 
Valkman said:
You can change the wires going into the bulkhead in the engine compartment. A bit easier then climbing under the das
Click to expand...
Agreeded, BUT then down the road you have just confused the issue if you have to trace out wires.
 
Diagnose it first. If the wires are reversed, find out WHERE they are reversed. They could be reversed at the gauge, or at the firewall connector. If it was mine, I would want it RIGHT.
 
^^^^^^^^^^^This^^^^^^^^^^^^^^

Can also do some quick testing to confirm its a wire crossed and not some other issue.
1. Engine off.
Open the door (dome light) and step on the brake (brake lights). It should show about 5 amps discharge.
if the needle movement is hard to see, shut the door, turn on the headlights.

2. Engine running at fast idle. (anywwhere from 1250 rpm to 1600 rpm depending on the step)
Check the voltages at the battery post, at the alternator output stud, at the ballast resisitor ignition terminal (blue wire).
At the same time check the ammeter.
This is just to eliminate the possibility the alternator output wire isn't well connected to the main splice.
 
'74 with a standard setup is basically wired like this.
upload_2020-4-19_19-27-19-png.png

'74 has the seatbelt interlock and other differences. The point is; the run from the alt out to the main splice should be a direct run with one connection (at the firewall).

However, if the car was equipped with a rear window defrost grid, the ammeter's post was used a distribution point for the alternator output wire (R6).
upload_2020-12-27_22-14-19.png

More about that setup here How rare is electric rear defrost?
 
RustyRatRod said:
Diagnose it first. If the wires are reversed, find out WHERE they are reversed. They could be reversed at the gauge, or at the firewall connector. If it was mine, I would want it RIGHT.
Click to expand...
You mean you don't like when the headlights all sudden get as bright as the sun as you start to smell melting wires as the amp gauge pegs? LoL

I agree.
Had my share of 'messed with wiring' on a few of my cars. You can always tell a bad re wire job, repair or addition.. because the car will go through regulators and even alternators like toilet paper. The amp gauge is always leaning toward the charge+ as well.
 
There is no possible way the ammeter wires can be anything eXCEPT reversed. Otherwise the charging system would not charge and the bat. would not read 14V

DISCONNECT the battery before screwing with those. They are large wires and ARE NOT FUSED except for the main fuse link which is uh...................undependable...........
 
You can pull out the cluster pretty easily and see if the wires are backwards the red side is marked with a big R! If that post has the red wire then you know the problem is something else. If its reversed you can fix it while you're there. To pull the cluster simply loosen the the two nuts that hold up the steering column, not all the way just enough to lower it to clear the cluster. Then take put the 6 screws the hold the cluster in. Reach in and pop the speedo cable loose and the cluster will slide out far enough to inspect the wiring without removing anything else.
 
Bypass that thing!
Or at the very least, always keep a 1/2" wrench in your center console or glove box to be able to quickly disconnect the battery when it eventually shorts out and putrid white smoke starts pouring out from the gauge cluster.
Don't ask me how I know.
Read this twice then do it.
MAD electrical ammeter bypass link
Catalog
 
Don K said:
Recently picked up a 74 duster and been working out the bugs. I found it was not charging replaced the voltage regulator and fixed the problem. About 14 volts to the battery but when I looked at the amp meter in the car it is reading discharge. So before I start tearing things apart any ideas? Amp meter cross wired?
Thanks in advance.
Click to expand...

Also know that the red wire goes toward drivers side of the gauge.
Just an FYI, if your gauge shows discharge at idle that’s normal.
At 1k in the rpms it should show a positive charge on the gauge.
If the more rpms you give it the more it moves to discharge then the gauge is hooked up backwards as discussed.
 
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