My '73 Duster 340 has been going dead on me lately and I am assuming it is the Alternator or voltage regulator. I first noticed the headlights getting bright and then dim and now if I drive at night it's only a matter of time before she dies. I checked a bunch of threads but didn't really find any advice on how to simply check out the charging system with a meter. Can someone run me through it. The alternator is a three wire deal and as far as I know everything is stock or stock replacements. Also, I noticed on one of the threads that Moparts had a orange street/strip voltage regulator for $40.00. Is this worth looking into?
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Need help checking Alt and regulator on '73
- Thread starter spence340
- Start date
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nothingbutdarts
Well-Known Member
Multimeter tests. First start the car and check the alt. output voltage (the big wire of the three going to the alt.). A correct reading should be around 13.8 to 14.2 volts. It should have at least battery voltage otherwise you have a bad output wire to the battery.
If it's just showing battery voltage and nothing higher than: unhook both the field field wires going to the alternator (the two smaller push on connectors) then get two jumper wires. Take one of the jumper wires, put it on one of the field terminals at the alternator and the other end of that wire put it on a good engine ground. Take the other jumper wire and connect one end to the other filed terminal, start the car and have the voltmeter hooked up to the alternator output, then take the other end of the last jumper and touch it to the output terminal of the alternator, you then should see the voltmeter go up in voltage quite a bit and hear the engine load down a little. By doing this you are "full fielding" the alternator and putting it in maximum output which you don't want to do for a long time.
If this doesn't make the voltage go above non running battery voltage than the alternator is bad.
Check all leads going to the alternator and regulator as well as make sure the regulator has a good ground. You could unplug the regulator, with the key in the run position the blue wire should have battery voltage and the green wire if still hooked to the field terminals of the alternator should as well have battery voltage.
I know nothing about the voltage regulator you are asking about.
If it's just showing battery voltage and nothing higher than: unhook both the field field wires going to the alternator (the two smaller push on connectors) then get two jumper wires. Take one of the jumper wires, put it on one of the field terminals at the alternator and the other end of that wire put it on a good engine ground. Take the other jumper wire and connect one end to the other filed terminal, start the car and have the voltmeter hooked up to the alternator output, then take the other end of the last jumper and touch it to the output terminal of the alternator, you then should see the voltmeter go up in voltage quite a bit and hear the engine load down a little. By doing this you are "full fielding" the alternator and putting it in maximum output which you don't want to do for a long time.
If this doesn't make the voltage go above non running battery voltage than the alternator is bad.
Check all leads going to the alternator and regulator as well as make sure the regulator has a good ground. You could unplug the regulator, with the key in the run position the blue wire should have battery voltage and the green wire if still hooked to the field terminals of the alternator should as well have battery voltage.
I know nothing about the voltage regulator you are asking about.
nothingbutdarts
Well-Known Member
Thanks, when I go to the garage tomorrow night I'll check it out. When I check the alternator with the meter I am assuming one lead to the black large wire and the other lead to a good ground, correct?
Yes, the black meter lead to a good engine ground and the red meter lead to the large black alternator wire. Start your testing by checking the battery voltage before anything else. The red meter lead is the positive lead of the meter all the time. Next measure voltage at the alternator without starting the engine, the voltage should be the same as the battery voltage you just checked. Then do the "full field" test as I mentioned.
Kim
The battery reads a solid 12.31 but the Alternator is reading around 9 but the read out is all over the place. My tester is a Craftsman unit and may be messed up I guess. Also, I thought the voltage regulator was the chrome piece on the side of the fender but as I was cleaning up the ground on it I noticed the mopar voltage regulator on the firewall. What is the unit on the fender?
nothingbutdarts
Well-Known Member
The battery reads a solid 12.31 but the Alternator is reading around 9 but the read out is all over the place. My tester is a Craftsman unit and may be messed up I guess. Also, I thought the voltage regulator was the chrome piece on the side of the fender but as I was cleaning up the ground on it I noticed the mopar voltage regulator on the firewall. What is the unit on the fender?
If you are talking the drivers side fender it would be the engine ECU/electronic ignition ECU. The item that has been posted on here asking if the orange box is good or not! It should have a strange shape connector on it with five or four wires going to it.
Is that battery reading both running and with the engine off? Is it a steady reading? If so there most likely is nothing wrong with your meter.
Where were you taking the 9 volt reading at? The big black wire I would guess. If so you really should have gotten at least the battery voltage reading of 12.3 volts. Where did you have the ground clamp of the meter while reading the alternator?
Did you try running the jumper wires to the alternator field like I suggested?
Well, it looks like it was the regulator, lights and everything look fine after I changed it out. Nice to see the dash lights again. I am a little concerned about the battery voltage though, it seens to be around 15 volts now at idle. Is that too much?
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