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post #1 of 1 Old 10-03-2005, 01:44 PM Thread Starter
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How To: External Voltage Regulator

How To: External Voltage Regulator w/pics.

I just installed an external voltage regulator (VR) on my 86 GLH. Is there any interest in seeing a how to with pics for dummies? I know there are dozens of posts on the topic with varying text instructions, but I have seen a lot of posts that people are still confused on how to do it. If there is interest, I will post some pics to go with the instructions.

External Voltage Regulator Install How To (1986 Omni GLH, other vehicles similar)

The Problem:
Alternator not charging (output below 12.8v volts) or alternator over charging (output 14.7+ volts). When the voltage regulator (VR) fails, in most cases it will fail “open” (no charge) but it can fail “closed” and cause and overcharge. Complete basic troubleshooting (a good outline of that is here: http://minimopar.knizefamily.net/charging.html#charging) to determine if the VR has failed.

The Culprit:
Your voltage regulator is located in your power module (PM, computer next to battery) in your 85-87 Dodge. (In later years, the VR is also in the main computer under the hood?). This built in VR seems to be failure prone, and renders an otherwise good power module useless.

The Solution:
Use a tried and true electronic external voltage regulator to control your alternator output. These regulators were used for decades on older Mopars, and are very reliable. Any VR from a 70’s or 80’s truck or RWD car will work. They are less than $20 new, and nearly free used. There are numerous regulators from different makes that will work, I used a Mopar one because that is what I had. By tapping in to the existing wiring, we will maintain the use of our factory volt gauge. It will also allow for easy switching back to an internal regulator should you happen to find a working PM.

Parts List:
  • Mopar Voltage Regulator
  • Plug with pigtails for regulator
  • 3 x 18” 16awg wires (preferably green, blue and black)
  • 1 x crimp loop connector
  • Electrical tape/ shrink tube
  • Solder
  • Zip Ties
  • Wire loom
  • 2 self-tapping sheet metal screws

  • Drill & 1/8” bit
  • Screwdriver
  • Soldering Iron
  • Volt meter
  • Wire stripper/knife
  • Crimping tool
  • Wire Cutters
  • Pin-out diagram as found in Service Manual

  1. Place VR on driver side shock tower next to relays. Mark and drill holes for mounting.
  2. Solder the blue and green wires to the blue and green leads on the VR plug. If your wire colours don’t match, don’t worry. As far as I know, these two connections are interchangeable. The green wire went to the center pin on my VR, blue one to the side pin on mine. Tape/shrink wrap connections.
  3. Crimp loop onto end of black wire.
  4. Screw VR to shock tower. Connect black wire w/loop to one mounting screw, and plug in your pig tails. Good grounds are important here.
  5. Examine the upper plug on your power module (or only plug on newer cars). A pin-out diagram is helpful here. Locate the 2 field wires from your alternator. Mine had one black, one green. Confirm by checking each for continuity to appropriate field terminal on alternator. Locate the J2 (key on hot) circuit on the same connector. Mine was a heavy dark blue wire. Confirm 12v at key on.
  6. Unplug the upper plug on your power module (or unplug your computer on later cars).
  7. Disconnect battery, even though it is dead anyway.
  8. Strip 1/2”-3/4” of insulation off each of the three wires you just identified. Do not cut them.
  9. Solder the green wire from the VR to the green field wire, the blue wire from the VR to the blue (“J2” switched 12v) and the black ground wire to the remaining alternator field wire. Tape connections thoroughly.
  10. Use the wire loom and zip ties to route and secure wiring.
  11. Reconnect computer and battery, start car and test for voltage.


With a working power module, my car put out 13.5 volts. With the external regulator, the car put out 14.5 volts.
The black ground wire attached at the VR mounting screw can be omitted if the untapped field of the alternator is simply grounded to the case. I chose to add the wire to the harness to make for easy switching between external and internal VR’s if required (unplug one, plug in the other).
I do not know what will happen if the external VR is installed in this manner with a shorted close or a functioning power module regulator (i.e., it may be necessary to cut or disconnect the field wires from the harness to the computer, rather than simply tapping into them).

Disclaimer: This is the procedure I used to repair my 1986 Omni GLH. Other power module equipped cars should be similar. This repair should also work on SMEC/SBEC cars, however I make no guarantees as to the suitability or safety of this modification for any application.

86 GLHT Santa Fe Blue
1989 Caravan Turbo

Last edited by Frank; 10-03-2005 at 03:22 PM.
william is offline  
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