Wiring for 2 plugs to replace a 2-in-1

Figure 1. (a) 3-wire circuit. (b) 2-wire circuit.

• You need a 3-way (as in "positions"), 2-pole, centre-off, switch for each blind. ( Note that "3-way switch" in North America means a two-way changeover switch as used in stairs lighting.)
• Figure 1a shows how to wire it with three wires assuming the end-of-travel switches are installed in the motor mechanism. As drawn, the motor will run until the open position is reached. The OPEN limit-switch will open and stop the motor. By switching SW1 the motor will run until the CLOSED switch opens upon which the motor will stop.
• Figure 1b shows how to reduce wiring to 2-wire by the addition of a pair of diodes. As shown, current will flow through D1 until OPEN opens, as before. When SW3 is reversed current can flow through the CLOSED switch and D2.

We have no idea if the switches or diodes are in your blinds mechanism at this time.

[$20 Innova 3320] is a pretty decent multimeter

See http://www.eevblog.com/forum/testgear/innova-3320-multimeter-teardown/

Consider 2nd hand fluke

what happened?

Any of

• You had the red lead in the 10A socket even though the dial was set to ACV~.
  • Unlike better multimeters, that socket is unfused in this low-cost meter because decent 10A High-Rupture-Capacity fuses are expensive.
  • Some better meters have a "jack alert" feature to warn of this problem.
• You didn't have shrouds on the probe tips and a tip slipped and shorted two contacts, not just the one you were trying to probe
  • Trying to hold two probes and a multimeter with only two hands can be awkward. This is why other voltage test devices integrate the electronics and display into a probe.
• It's a three-socket meter with mA~ and ACV~ measured from the same sockets. This is a common design issue in low-cost meters. It is too easy to have the dial set to mA~ instead of ACV~ or for a fault in the dial mechanism to leave the sockets shorted by the mA shunt. Four-socket designs are arguably safer.

one of my probe leads melted.

That shouldn't happen on a decent multimeter. The 10A range should be protected by a 10A HRC fuse and the leads should be rated for 10A. On the whole, it is better to blow a replaceable HRC fuse than to melt something you are directly holding while it is passing >10A at 120V.

one of the screws coming out the side of the switch got black from the spark.

It might be safest to replace the switch.

Related

• Electric shock - was I stupid, unlucky, or a combination of both?
• When doing electrical work, what do I use to check wires are safe?