Prepare the chassis.

Drill a hole centered in each of the two "short" sides of the case sized for the CG-16 cable gland. Drill a hole sized for the L6-20 receptacle. The hole should be centered horizontally on the panel, but the top edge should be as close as possible to the top of the chassis - 1/4" would be ideal. Once the hole is drilled and sized properly, remove the two mounting bolts from the receptacle's mounting wings and discard them. Hold the receptacle up to the outside of the chassis and mark the holes in the wings on the chassis. Drill 9/64" holes for the mounting hardware.

Drill holes sized for the pilot lamps in three of the four corners of the lid.

Prepare the mounting plate.

Lay the plate on your work surface and position the relays as close as possible to one of the long edges. The three relays should have about a half inch gap between them for air circulation, and the middle relay should be centered on the panel horizontally. Mark the 6 mounting holes (2 for each relay) and drill them with a 9/64" drill bit. Mount the relays using 6-32 x 1/2" bolts, lockwashers and nuts. The 240 volt relay should be on the right side, the two 120 volt relays on the left and in the center.

In the bottom left corner, drill a 1/8" hole for the self-tapping screw that comes with the ground bar. Make sure there's enough room around the ground bar so that it doesn't impinge on where the 220 receptacle will be, nor the incoming cable (through its gland) on that side of the chassis. Mount the ground bar in the hole and screw it down tightly.

Install the mounting plate in the bottom of the chassis with its supplied hardware.

Cut two 2 foot lengths of the SOOW cable. Prepare each by stripping 6 inches of the outer jacket on one end and 2 inches on the other end. On the short end, install a 120 volt plug. Be sure to connect the black wire to the hot prong, the white wire to the neutral prong and the green wire to the ground prong. Run each cable through a cable gland, making sure the loose 4 inches of wires are on the inside and the plug is on the outside. Attach each gland to the chassis.

Strip the outer jacket off the remaining 2 feet of SOOW cable. Cut a 4 inch length of each of the white, black and green wires. Attach them to their respective terminals on the L6-20 receptacle. The green wire goes to the ground terminal (which has a green screw), and it doesn't matter which of the other two is black or white. Install the L6-20 receptacle in its hole in the chassis. Make absolutely sure that none of the wires or any metallic parts of the receptacle contact the mounting plate!

Connect each of the green wires - one from each of the 120 volt plugs and the one from the L6-20 socket - to the ground bar, trimming them to length in the process.

Strip 1/2" of insulation off of each black and white wire from each 120 volt cable.

Cut a 3" piece of 22 gauge wire and strip a half inch of insulation off of each end.

Strip 1/2" of insulation off each of the two wires from each of the two pilot lights that share the same long edge of the lid.

Take a 12 gauge QD crimp terminal and insert one of the white wires and one of the wires from the associated pilot light. Crimp tightly.

Take another 12 gauge QD crimp terminal and insert the black wire from the same cable and one of the short 22 gauge wires into it. Crimp tightly.

Take the other end of the 22 gauge wire and the remaining wire from the pilot lamp and insert them into a 22 gauge QD terminal. Crimp tightly.

Connect the QD terminal with the 22 gauge wire and the pilot light wire into one of the coil terminals of the associated 120 volt relay. Connect the QD terminal with the black 12 gauge wire into one of the two line side switch terminals. Connect the QD terminal with the white wire and the pilot lamp wire to the other coil terminal of the relay.

Repeat this step for the other cable, pilot lamp and 120 volt relay.

Designate one of the 120 volt relays as the "white" relay. Designate the other as the "black" relay.

One of the line side poles of each relay should have a single switch terminal connected at the moment. From the load side of that pole to the unused line side of the other 120 volt relay, measure for a piece of 12 gauge wire from the wire set aside earlier. Trim 1/2" of insulation off each end and insert into a QD crimp terminal and crimp firmly. Use white wire for the white relay and black wire for the black relay. Again, you're connecting the load side of the relay terminal coming from the 120 volt cable to the line side of the unused pole of the other relay. This step is a little tricky to describe, so refer to the schematic.

From the remaining unused load side terminal on each 120V relay, measure for a wire to reach over to the line side terminals of the 240 volt relay. Cut the appropriate lengths of wire and strip 1/2" of insulation off each end. Cut two more 3" pieces of 22 gauge wire and strip 1/2" of insulation off each end. Take one 12 gauge wire and one 22 gauge wire and insert one end of each into a QD terminal and crimp firmly. Crimp the other end of the 22 gauge wire in a 22 gauge QD terminal, and the other end of the 12 gauge wire in a 12 gauge QD terminal.

Connect each of the two "double wire" QD terminals to the line side switch terminals of the two poles of the 240 volt relay. Connect each of the 22 gauge wires to the coil terminals of the same relay. Connect each of the 12 gauge "single wire" QD terminals up to one of the remaining unused load side terminals on the primary relays.

Trim 1/2" of insulation off each of the wires of the remaining pilot lamp. Trim 1/2" of insulation off each of the two hot lines coming from the L6-20 receptacle. Insert each hot line and one of the two lamp wires into a QD terminal and crimp securely. Connect each of the QD terminals to one of the load side terminals of the 240 volt relay.

Take a moment to inspect the wiring. Follow the high current path from each hot line in the input cable to the output. Make absolutely sure that at no point the high current path is run through one of the 22 gauge wires - those should only be used to transfer power from a switch connection over to a relay coil. Insure also that there are no loose crimps, stray wire strands or short circuits.

Attach the lid with the supplied hardware, insuring that none of the wires are pinched between the lid and the chassis.

Testing

Plug each 120 volt cable - one at a time - into a 120 volt power strip that is switched off. Switch the power strip on and observe that the associated relay clicks on and that the pilot light lights up.

Next, plug each cable into outlets on separate circuits. You may have to hunt to find two that are on opposite phases. You may need an extension cord to make them reach. Make sure to use a heavy duty cord for this purpose.

When you find two outlets that work, the third pilot light will light up. At this point, the device should be operational.