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1977 620 coil/distributor wiring

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Hi all,  


I've searched for this and have found a lot close and all of the threads with schematics/files no longer work. 

So, I just picked up a 1977 620 (already had a 79KC) the '77 runs excellent at idle, but if you try to run it up to highway speeds it starts missing like crazy and looses power bad. Just started doing some thumbing around and noticed the coil/resistor/distributor seems wired incorrectly. I have black/white + wire that connects to the resistor. Then, from the same pole on the resistor i have a white/black wire that goes to the + side of the coil. Then there is a yellow (looks like a repair job) wire that goes from the coil - to the distributor (single point). This all seems ok, other than the fact that it's not actually using the resistor... The coil has verbage on the side of it stating that it must be used with a resistor. 

Do I simply need to move one wire to the other side of the resistor? It looks like the PO had recently put the cap/rotor/points in this thing and the points are already looking burnt up. I also checked base timing just because and its at about 18* (I believe 13.5 is spec.) and there is no vacuum line to the advance.


Anyways, I'm assuming I need to actually use the resistor, probably replace the points again, hook up a vacuum line and then get the timing adjusted right. Are any of the things done something that are a (trick of the trade) type fix that I should leave alone?


crappy night time cell pic for the inquisitive :)




Thanks,    Hillbilly

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There should be a power wire from the ignition to the one side of the ballast resistor and from there to the coil +. It will have power only in the START position.



There should be a power wire from the ignition to the other side of the ballast resisto. It will have power in the ON and START position.




a/ In the ignition key in the ON position... there is power through the ballast to the coil that is reduced to about 8 volts to prevent burning the points out and over heating the coil. 


b/ In the START positio,n power is fed directly to the coil, by passing the ballast. This gives a full 12 volts to the coil during cranking for greater spark plug voltage. 


When the engine starts, and key is released the ignition switches from b/ to a/ and voltage is passed through the ballast resistor.



I can post the wires that do this when I get home today if someone else doesn't.  


Yes running a full 12 volts will work but the points will only last 50-150 miles and the coil can easily over heat and fry itself.

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If this is a point coil YEs you need to use the resistor.


the blk wht wire always fees the resisitor then foes throw the resisitor to the + side coil.

the points wires should go to the - side of resisitor somw how.Depends on if dual point or single most like you can just route it to the - side coil.


the HOT start wire(key in START) will go to the + side coil some timer it might be on the balssta but long as it hooked up to the +side coil when in START then once started the key will go to ON and feed the power to the coil via the ballst to keep it from arching out the points(buring up) replace the condensorr also maybe.


remove starter wire then tun key to Start and see where the START wire is at. Unless this was a EI dizzy rig before then got converted back to points.



also 18 degs is a bit much at idle .

Hard to tell from my chair but make sure the dist rotor is pointing directly at #1 plug wire at Zero on crank. if not then a dizzy mount might have gotton swapped or what ever maybe a oil pump installed wrong.


olddatsuns.com has everything in the Tech section

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Non California '77 620...


a/ With the ignition key in the ON position... there is power on the Black/White stripe wire to and through the ballast to the coil + terminal. The ballast reduces the voltage to about 8 volts to prevent burning the points out and over heating the coil. 


b/ In the START position there is power on the Black/Red stripe wire fed directly to the coil + terminal, by passing the ballast. This gives a full 12 volts to the coil during cranking for greater spark plug voltage.


c/ There should be a Black/Blue stripe wire on the coil - terminal that connects to the distributor points that open and close to ground.




On one of your wires looks like the insulation is burned off.


Set the timing to 12 degrees and then connect that vacuum advance up afterwards. When working properly the vacuum advance makes the engine more responsive at part throttle.

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  • 2 weeks later...

Thanks for the help fellas. I got it all changed over and the timing set to 12* Took it for a little drive and the miss is all gone :) Still a little down on power compared to the KC, but I haven't done any other tune-up work to this one yet and the fuel filter has a nasty pile of rust sitting in the bottom so its probably been a little neglected and needs a good once over.


Thanks again.

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