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Submitted By: offroader_dodge
Date: May 8, 2010, 09:47:08 PM
Views: 6503

Summary: After diagnosing a bad computer that wont turn on the alternator,here's what a person can do to save a few dollars. Starting with 1988-up efi/diesel vehicles (excluding 1988 carb 360) the alternator was controlled by the pcm. If it fails to charge, you may have to pay $300 for a new pcm. Furthermore, if you convert to carburetor, the pcm will no longer work to control alternator. Here is the $20 long term fix, by converting to external regulator found on 1987 and older vehicles.

External Voltage Regulator Conversion -(offroader_dodge)

So,if you are reading this i assume you have proved your truck's computer refuses to excite the alternator.

What my intentions are is to give you my version of regulator retrofit and you can comment/improve on it from there.

You will need:
  • 1987-older external regulator
  • pigtail connector for regulator
  • misc wire/connectors for splicing

You can buy the connector and regulator from most any auto parts store or online. The colors on the pig tail will match, being green and blue.

The alt has 2 small wires on the back of it. The blue is + from a switched source, and a green -. The green originally ran to your pcm, but will now run to your external regulator. A + wire is also added to the external regulator as well. This wire senses battery voltage and tells the regulator how much - to apply to the green wire.

I pulled the alt connector and determined it had the 12v source,then full fielded it to prove the alt worked. This is done by grounding the green terminal on the back of the alternator while the engine is running.

I then verified wiring to computer was intact,which in fact it was.the blue wire is B+ and the green wire is the charge trigger wire.or regulator controlled ground.

I chose to inline splice the wire in case it didnt work and it was easier to return to original.

mounted regulator.

found ignition power and connected regulator wiring. If you still have fuel injection, the ASD fuel pump relay next to here is also a suitable place to hook up your blue + sensing wire.

with connections made i started truck and tested for charging voltage

secured wiring and took it for a 200 km gravel road test.

things i may consider next time: mounting reg to firewall instead of inner fender.
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