{Chrysler 300} mechanical one wire Voltage Regulator on alternator

[John Grady <jkg@xxxxxxxxxxxxxxxxx>]

Hi ,
Got into this pretty good today , thought I would share . 

May help someone —While needle jumps around some ,that is totally  normal , unlike modern electronic —  especially just after start , but continued wild fluctuations 30 minutes later are an indication of problems . Same unit is on all mopar 60 - 70 approx . And millions of them worked fine .  Electronic aftermarket upgrades were a disaster for me , 3 x , unless you also change to later two wire alternator design and its mopar silver box  regulator , —- using a 78 dodge truck listing  gets you those parts , you need pigtail too . . But you must add a wire for 12 v ( blue) to the feed in end of ballast R to one alternator  flag and use old wire for other flag to green wire of silver box . 

The one commonly sold as “electronic one wire  upgrade “ with red wire hanging out is the worst , total junk , fails by shorting which boils battery and can burn up alternator .The normal failure mode of a hot transistor is to short  , giving full charge .I cut one open , junk , tiny IC inside .  I have never used the mopar one , recommended with electronic ignition . Don’t  know 
So I like the mechanical one , Rock auto sells “standard motor parts”  , nice one seems identical to original inside and inside  . Good prices right now .. 
So after a few of these over a 100 k mile period , a relatively new one started acting up.
 .
I took apart and a crater had formed on one side and little peak on the other side of upper VR contacts .. The cause of constant crazy ammeter .  
You can check adjustment of assembly by the gap of arm contact to lower point it was .023 on mine . Don’t lose this (!) . Do not loosen 1/4” adjustment / clamp screw , in fact tighten it so it will not move at all . 
The upper contact on mine started to open( to reduce charge)  at 13.8 v , about right . That adds a resistor to field to cut the output , probably down to 5 A or less, so , once charged fully , it stays  open , hovering between upper and lower . In between it vibrates on and off on top one regulating current  output . It adds about 10 ohms ( the physically larger resistance underneath )— in and out . That arcing eventually burns points but over a long time  . An open 10 ohms will cause bad arcing and wild swings . My R  was ok. 
If , say on a sunny day with no load at all and the volts get too high on low charge  it pulls down all the way and actually shorts out field momentarily on lower contact and now vibrates on lower if needed  but that rarely happens . 
So although it sounds animal , the best way to fix this is to measure lower gap , we want to return to that number , mine was .023 . 
Then just just bend up the top contact with needle nose , for access and then with point file, file flat any peaks . Remove minimal amount of special contact   material , don’t worry too much about divot if near and edge  
this will slightly increase .023 , so bend back down to that number after “ surgery” or to your number and be sure to get contacts parallel and centered , and same number you had . Mine were  not centered , met at an angle  it was  burning at one edge = poor QC 
. The gap to magnet is super critical not just the points —why we do not touch adjustment screw . or take it apart . Same with lower point . 
The other skinny resistor is in parallel with the field and damps out a big spark when points are opening . I think it is about 20 ohms 
To measure resistors , put a piece of paper into upper contact , then measure each underneath ; actual value not critical , but if open ( high ohms ) it is defective . Without paper you get wrong readings . 

If you short the field wire to alternator accidentally , a thin wire inside VR acts as a fuse and melts ( obvious) . That avoids burning the harness . 
THIS one you can fix , and keep going … !
jkg 
Sent from my iPhone

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