found extra 3 prong male plug heater only works on hi

[bd]

Sorry for the delay, been under the weather.

Just to be clear:  The blower only runs on high speed; and only when the blower switch is set to high.  It doesn't run at high speed on all switch positions.  True?

Unplug the blower relay.  Temporarily jumper the blue wire to the purple wire.  If the voltage measurements are the same, replace the blower motor.  If the voltage measurements change or the blower starts working, replace the bower motor and the relay.

Took voltage readings as follows... 11.68v on high and 11.62v at the other settings.  Very confused.  Is the speed controlled by reduced voltage or reduced amps? or both?

Voltage, current and resistance are related in a very exact way, represented by Ohm's Law:  Voltage = Current X Resistance (Volts = Amps X Ohms).  If resistance is fixed at a constant value, then a decrease in voltage will cause a decrease in current.  Similarly, an increase in voltage will cause an increase in current.  The resistor uses some of the voltage across the blower circuit, wasting it as heat, hence causes a decrease in voltage available to the motor.

With regard to an electric motor there are other considerations, because of the magnetic field - the interaction between the magnetic field and current flowing through the motor windings that causes the effective resistance (reactance) of the motor to vary from its measured resistance.  But, even with the added complexity, it still boils down to the mathematical relationship represented by Ohm's Law.

[pholliday1]

Correct motor only works when switch is on hi and it will not work at all in any other position. Here is a picture of the three prong plug sorry its sideways.

[pholliday1]

Looks like pictures shows up correct when i opened it. I for got to add that I could "hear" the blower motor relay sound like it was working when I changed fan speeds.

[bd]

The only concern with the blower relay is whether the low speed points are burned (usually, this isn't a problem).  Burned low speed points will produce lower voltage readings at the motor than when the relay is temporarily bypassed using a jumper.  Hence, that extra step.  Bottom line, I think, is a bad blower motor, but now you have a way of checking the relay, too.  Let me know how it turns out.

[pholliday1]

How about my mystery plug?

[bd]

I tried resizing the image to get a closer view of the housing, but there's not sufficient resolution to see details.  The housing hints at being cobbled to add a 2-speed resistor.  I don't recognize its intended purpose or recall ever seeing that configuration.  Perhaps one of the other fellas can offer some insight.  Open a pole:  1) Factory, 2) Aftermarket.

[pholliday1]

I think I figured it out I believe it's for a suburban rear air setup.

[bd]

That could be - strictly for use with rear heater, not A/C.  Driver had control over the rear heater fan through an accessory switch mounted next to the ashtray.

[pholliday1]

Your correct extra plug is for rear heat. Problem turns out that the blower motor relay was bad. Thanks for the help BD