{Chrysler 300} Re: Non 300 12v power source

I don’t know that model mopar specifically but if two or 4 pin resistor on firewall one side of R is 12 v ignition feed hot — but usually only after starter is off . usually a blue wire in other mopars . Get vehicle wiring diagram . The other end of resistor went to + coil then after coil (-) to mopar orange box , or points — that is the wrong end to get 12 v . But there may be another wire there on the coil end of resistor on some mopar going back to start 2 , ign switch ——what this is about is on some mopar the blue ignition power goes dead on purpose during crank and power comes on at s2 of ignition switch ,they ran power during start direct to coil with no resistor . ( hot spark during crank ) .

That complicates all this . Crude way is short out resistor with aftermarket ignition but S2 will then power other ignition loads backward . It sounds like you went to wrong end of resistor as S2 / coil wire end goes to full 12 only during crank . Car would start, then stall . Other way , May not start well but will run .

Try just moving MSD feed wire to ign end of resistor . Note burned resistor , stock wiring also will start but not run …

Right way is add a relay , two 1 N 4007 diodes feed relay coil , bar end of both go toward coil + , the wire from S2 feeds one diode other diode fed by ign hot . That way full 12v out of relay is “on “ from either one . But no feedback happens Feed the relay arm with 20A fuse to alternator hot wire at ammeter or to stud on alternator . Going direct to battery will prevent the ammeter from reading ign current . This also gives a powerful “ign on “ new source that says on — start or ign on

This ignition wiring problem with Mopars confuses many people . Intent I think was to shut off everything else while cranking why S2 is on switch . S1 pulls in starter . Cannot use S1 for both purposes as 12 v on ignition wiring after start would feed back , make starter come in all the time .

Hope this helps you …

John
PS Bob , might put this info put in tech pages , errors around wiring resistor are common , involves VR wire/ alternator power 12 v too

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On Jan 4, 2023, at 1:07 PM, Dave Dumais <dave.dumais@xxxxxxxxx> wrote:

Hello John.

I have a 74 Dart with a 413 4 bbl.

I switched the 300 distributor and c oil with MSD coil and HEI distributor.

I need a strong 12v connection, hopefully inside the engine compt

The distributor connects to the coil, and coil needs strong 12v source for + terminal

Do I connect to the firewall resistor ?

Thanks,
Dave

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