CJ750 toolbox

Installing a 12V solid state regulator by Rich Hahn

The purpose of the article is to install the 12 volt solid state voltage regulator part number SMP124 or its equivilant VR650. The same part is available from other manufactures under different part numbers. The standard CJ unit has two wires attached to it. Since there is no consistancy to the wire colors, a method is required to identify each wire and where they go to correctly install the new solid state unit which has three wires.

The new unit has three wires, black (or dark brown),red and green in a three prong plastic jack. Cut the jack off and prepare the three leads. Remove the headlight and locate the indicator light for the alternator. Identify the two wires that connect to the indicator light. One wire is the hot lead that picks up voltage from the screw terminal strip (hopefully). The second wire from the indicator light connects via a "push on" connector to another wire in the harness within the headlight shell. Do not go further until you have identified these wires.

Disconnect the wire from the "push on " connector. Again, this is not the hot lead that goes to the screw terminal strip.

Using an OHM meter or any other device to check for continuity, insert one probe into the female "push on" which is part of the harness and the other probe to one or the other wire ends that connect to the old voltage regulator. When you find the one wire that has continuity, connect this wire to the red wire of the new regulator. Connect the second wire to the green wire and the black wire to ground. Reconnect the indicator light lead and you done.

As additional information, The red wire is the D+, also known as the "dynamo armature". The green is called the DF or "dynamo field" which goes to the rotor.

The indicator light is an intergal part of the charging system. Unlike any other bulbs that ground back to the frame, the alternator indicator light picks up positive voltage from the terminal strip but instead of grounding to the frame, the voltage travels thru a wire (the one you just identified above) and goes to energize the electromagnets in the alternator via the diode board. Once the engine starts and becomes self energizing, the voltage regulator senses this and shuts off the voltage going to the electromagnets by opening up the crcuit.

Once the circuit is interupted the indicator light goes off. The point being, if you have a dead bulb, the alternator will not charge.

One additional step in preventing charging problems is to install a wire from the diode board chassis to the engine block for a good ground. Over time, corroision may interfere with the diode board being grounded properly which will create problems.