Depending on the connection, it is possible the circuit is running thru the motor commutator thru the motor coil back thru the commutator to the drum switch.  The motor winding could be read as a short circuit depending on how the Ohm meter is set.

On 8/31/21 12:37 PM, G K via groups.io wrote:

When checking continuity with my voltmeter, I am showing a closed circuit between T1, T3, and T2, T4.  Is this expected, or is there an issue within the motor?

On Tuesday, August 31, 2021, 08:43:13 AM CDT, Ray De Jong via groups.io <dejongray@...> wrote:

The Jumper terminal screws may have been a bit loose and arcing occurred and the resulting heat build up probably fried the wire. I have replaced many receptacles that fried not only the lead-in conductor but also the inside of the outlet, all from contacts losing their tension an/or a loose connection

On Monday, August 30, 2021, 6:34:26 PM PDT, G K via groups.io <bug_hunter2000@...> wrote:

Working on the SB9 tonight, and smelled a little burn.  Flipped the switch off. looked around and saw no issues.  Flipped it back on and pop goes the breaker, and smoke from the switch.  I believe the switch is the original (1942) drum switch.  Unplugged it, and took the cover off the switch, and the jumper was fried.  No idea why.  I'm not an electrician, but can use a voltmeter.  Suggested troubleshoot? 

120 volt circuit. Furmas R44, 6-terminal switch, Dayton 3/4 hp motor.

I'm planning on pulling it apart tomorrow and look for any additional burned wires, but I do not believe I will find any from a cursory look.  Then I'll wire a receptacle directly onto the motor to see if there are any issues there.  If were good there, I will re-wire the switch and see what happens.  Maybe some chips got inside and caused a short.  Not sure.  Any chance capacitor went back and caused the short?  The only burn smell is in the proximity of the switch, but that could be where the smallest gauge wire (jumper) is located.

Thanks,

Greg