Dash amp meter gauge shows neg when engine at idle

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olddman

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My 65 Dart amp gauge reads negative when the engine is at idle. Idle is about 750 rpm. If headlights are turned on reading gets worse. As soon as rpm is increased the reading goes to positive. Battery and alternator (square back style) check out as good. Have replaced the voltage regulator, cleaned the plugins at the bulkhead, cleaned connectors at the start relay, cleaned battery terminals, cleaned grounds from battery to engine, engine to bulkhead. Took car to three different parts shops and had tester connected to battery and with engine running the tester showed no charging. What do I check/do now?
 
Does it put out adequately "just off idle?" This may be "normal" depending on which alternator and the size of the pullies.
 
Sounds like a normal Chrysler product if I ever heard of one.
 
olddman said:
What do I check/do now?
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Drive it, and enjoy it. Although an alternator SHOULD charge fine at idle, the old systems don't always. I guess if you got stuck in traffic for a REALLY long time at idle, it could be a problem, but as long as you are charging at off idle, I wouldn't worry too much about it.
 
ir3333 said:
that is normal...the fix is to convert to dual field alternator
Click to expand...

Curiously, are the newer style voltage regulator connectors available or would you need to find an old one?
 
Oaktree said:
Curiously, are the newer style voltage regulator connectors available or would you need to find an old one?
Click to expand...

not sure,it's been a long time since i did a conversion.They are probably avail. new but shouldn't be
too hard to find used.A worthwhile modification...idling at night your lights are pretty dim if you leave
it stock.
 
ir3333 said:
that is normal...the fix is to convert to dual field alternator
Click to expand...


"Dual field" is not technically correct, it's "isolated field." But that does not change a thing unless two conditions are met with this change.........

1....You need to use the improved "square back" design, as "round backs" were used for a few years after 1970

2....Not all squarebacks are created equal for low RPM output. Bigger is not necessarily better. I think the 46A unit is considered to be the low RPM "king." If you buy a rebuilt.........good luck on getting what they claim.

The fact is that mulluons and mulluons of these cars were driven bulluons and bulluons of miles, and they worked just fine, "back then."

billions-and-billions.jpg
 
OP already has the squareback alternator. It should work as well with the original Vreg, i.e. "high-side control" especially since the new Vreg is likely electronic (if no exposed resistors on underside). With a 1965, he doesn't need to worry about the notorious "bulkhead meltdown". Extra resistance in the sense and ground wiring will cause "too much" charging. Slight discharge at idle is fairly normal. If the battery stays charged over a week of driving, you have no issues. They stopped putting ammeters in cars in the 1970's because they confused drivers, and routing the high charging current into the cabin can cause problems (see "MAD Bypass").

For more diagnostics, buy a cigarette lighter voltmeter. My newer Mopars show 14.3 V at idle, but those have the high output Denso alternators, needed for radiator fans and such. Put one in an older Mopar at your own risk to the wiring. OK if you know what you are doing and add underhood relays.
 
Thanks to everyone for the help in trying to solve my problem/concern. The battery has always stayed charged, and it sounds like a no charge indication at idle is normal. Will just go ahead drive and enjoy my old Dart.
Should something else come up I will be back for more help as I have before.
 
ir3333 said:
that is normal...the fix is to convert to dual field alternator
Click to expand...

I digress. IMO, there is no "fix" since this is normal operation. These cars ran for decades before dual field alternators with no problems.
 
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