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I have a 1940 120 Club Coupe. I have been running through electric components on the car. While operating the heater, I discovered the fan forward and reverse function for floor or defrost. I'm lucky that the switch does operate both ways and lights up too. However when you switch to the farthest position either way, the switch light not illuminate nor will the fan run. So is it the switch or the fan that's the problem?

Ask your voltmeter 😀

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It sounds as if you have the rotary style deluxe 2 speed reversing switch which I believe came along in 39 and was probably used with a different mounting in later models too. From the symptom you describe, chances are problem is in the switch.

The far position in either direction is for slow speed and that is controlled by having the voltage for those positions go thru a resistor which is selected and placed in the circuit by the switch. The resistor goes in series with the voltage being fed to the motor so the voltage is lowered. Since motor works at hi speed which gets direct battery voltage but not in the low position which needs the resistors, there is a good possibility the resistors are damaged, missing, or for some reason the wiper inside the switch is not able to connect and bring them in the circuit. I believe the light bulb is wired to be in parallel with the motor voltage feed so it would be bright at hi speed and dimmer in the low speed position. Since it too is acting up I doubt the switch is passing any voltage when at the second positions.

For starters, you might take a look at the rear of your switch and check for the presence of and condition of the resistors. I have one of the switches where a resistor for one direction is completely missing and here is a blurry photo of another forum members switch. His switch still works but the resistors (wire coiled objects in red circles) appear to be in poor condition.




EDIT: I just found a slightly less blurry photo of the deluxe switch on a Max Merritt deluxe heater and switch listing currently on ebay. The resistors on that second switch are not in great shape either with one completely missing the ceramic inner support and the other one looking almost ready to fall out. Make sure you have resistors and their wire ends are securely connected to the switch at each end. If that looks good then chances are the problem is internal or possibly something in the wiring is hooked up incorrectly. The field and armature are separately wired and brought out to the switch which places them in series so motor can run. The switch keeps direction of current flow thru one item the same in both directions but changes direction of current flow thru the other depending on side of switch the knob selects. That flow change in only one item alters the magnetic relationship between the field and armature to get the reverse direction.

For anyone interested, here is the heater motor electrical pathway thru the 39-42 ?? deluxe two speed multi position reversing rotary switch.

Referring to the second photo in the group, the battery is connected to the 4 terminals shown at the top of the switch, Direct battery voltage to the two labeled as BAT Hi and thru resistors, to the two labeled BAT Lo.

The wires to the motor armature go to the two semi circular contacts in the center of the switch labeled ARM 1 and ARM 2.

One wire going to the field connects to the long semi circular contact at the bottom. The other field wire connects to ground.

When the switch is off the small button on one of the two wipers (denoted by red dots) contacts dead space between battery Hi terminals so no voltage can be passed. Turning to the first notch in the direction labeled CW allows the first wiper buttons to connect direct battery voltage from BAT Hi to the terminal labeled ARM 2 which is sent to the motor armature. It returns from the motor via ARM 1 wire and armature is then connected via the second wiper contacts to the terminal connected to a field coil wire on the lower semicircular contact where it goes out to motor field coil and then gets ground thru the second field coil wire. The light bulb center contact is also connected to this second wiper so with the voltage at that point and the shell connecting to ground, it burns brightly. The motor turns one direction at hi speed.

Turning to the second notch just inserts the resistor into the circuit thus lowering the voltage and speed but everything else stays the same except with the voltage lower, the bulb is dimmer but motor still turns in the same direction.

To reverse direction, the knob is turned to the CCW side where the process is repeated except the pathway thru the armature is now changed. Power to motor is now via ARM 1 wire and back thru ARM 2 wire and then to field. This reversal of current flow direction thru the armature causes it to change magnetic polarity but with the field effectively staying at the same magnetic polarity since current flow is still via the same wire being connected to the lower terminal, the motor changes direction.

Here is the switch internals as well as a drawing showing how the deluxe heater is wired. NOTE: the wire colors on the wiring drawing are what another poster found on his heater but I cannot personally verify this is the way they are all wired because there were different versions of the heater and switch. For convenience I arbitrarily labeled the switch sides CW and CCW. I have no idea if this will be the direction the motor turns when installed.