OK, I've been chewing on this one all night....
I understand the theory behind PWM. However, in this case, we're still dealing with modulating the pulse width on a 12V DC voltage. So, no matter how much you modulate the pulse width, you're still going to end up with an effective voltage somewhere between 0V and the supply voltage for any givent current draw.
However, the exact effective voltage will be a function of the current draw of the item downstream. Pulse-width modulate to a dead short and the voltage will be zero. PWM to a resistor, and until you exceed the currenty carrying capacity of that resistor, the measured voltage will vary. Exceed that current carrying capacity, and the measured voltage goes to Vmax and the current remains constant (which is exactly what I'm seeing in 4high and 4low).
The amount of power is proportional to the duty cycle which is the percentage of time that the current is on.
http://en.wikipedia.org/wiki/Pulse_width_modulation
I understand what you're saying, but I believe that once the current carrying capacity of the resistive load downstream of the PWM source is exceeded, the voltage maxes out and the current through the circuit remains constant. I believe that's what we're seeing with the clutch coil here. Otherwise, when we apply a direct 12V to the coil, wouldn't the current through the circuit be three times greater than the current measured through it with a 33% PWM power supply?
Look at it another way: If I lock in 4high using the OEM system, and it calls for a 13% duty cycle, the system moves 4.31A of current through the clutch. Now, if we apply a constant 12V source to the system, shouldn't the clutch consume 7.5 times that amount of power?
We know it still flows 4.31A of current with 12V applied directly, so the clutch coil isn't consuming any more power. 4.3A is 4.3A no matter what the voltage, and in this case, we already know that the effective voltage as measured at the BWM switch 12V regardless of the source, so isn't the net effect the same power consumption by the clutch and, therefore, the same function?
Putting it another way, amperage flowing through the clutch is the same. (Effective) Voltage input to the clutch is the same. Therefore power consumption is the same.... isn't it? Is there an EE in the house??