Lindsay and Harold...
Here's the wiring diagram.
As you can see by tracing through the circuit, it is in 2WD in this diagram, the limit switch has it stopped, and it will do nothing.
When the switch is turned on (4WD position), the indicator will light showing that the 4WD is on, and relay one will activate.
this will send current to the limit switch and activate the limit switch relay, and will result in grounding the polarity reversing relays.
At the same time, the center two polarity reversing relays will come on, and will send current polarized correctly to make the motor turn the 4wd on.
When the 4wd actuator reaches the end of it's travel, it will change both limit switches.
This will turn the limit switch relay off, and kill the ground to the polarity reversing relays, stoping the actuator motor.
The indicator light will stay lit showing 4WD is on, but no other action will take place untill the switch is turned off.
When the switch is turned off (2WD position), the indicator will go out, and relay one will return to the static position.
This will send current to the limit switch, and because it was switched to the "4WD" position, it turns the limit switch relay on.
At the same time, the outer two polarity reversing relays come on and send current that is polarized to cause the motor to turn the 4WD off to the actuator motor.
When the actuator gets to the end of it's travel, it switches both limit switches and kills the limit switch relay.
This stops the ground to the polarity relays, and everything shuts off.
This circuit will work. It duplicates the original system. because there are no momentary controls, this system does not allow partial engage or disengage of the transfer case.
It also offers redundant safety against a stuck relay because it turns off the positive AND the negative to the motor.
I know that this schematic might seem a little complicated to those that are not used to looking at wiring diagrams, but trust me- it's really a series of simple circuits. The whole trick lies in building the harness.
When completed, the harness willl be layed out like this:
There will be a switch and an indicator in the cab mounted to the dash with one small harness going through the firewall. If desired, the switch on the shifter could be used and the indicator in the speedo assy too.
There will be a set of relays mounted neatly under the hood, and a set of power and ground wires. These will come from the same harness.
There will be wires attached to the actuator motor and limit switch on the transfer case.
Done properly, most folks will not recognize it as being home made.
Let me know when you're ready to build it, and we'll get after it!
After staring at this schematic for a while, I realized that the limit switch is rotary and may have both switches in the "on" position at the same time.
To avoid back feeding into the unused pair of polarity relays, i will add diodes.
These will appear on the diagram as soon as I can get it modified.
Diodes added to eliminate possibility of triggering all four polarity reversing relays.