How to adapt a Real Gear MIG135 to accept a Spool Gun

Disclaimer: I am not a certified welder or welder repairman.  I did this on my own and I do not accept responsibility if you damage your welder.

Several years ago I purchased a Real Gear Mig135 mig welder at my local GTS/Welco dealer.  They are now Praxair, but that is beside the point of this article.  6 months ago I was looking to do some aluminum welding, so I purchased the Real Gear Spool Gun, part number 102532, that is designed for the Mig140 (replacement for the Mig135) because I was told that it will work fine on the Mig135.  Well, it doesn't.  

Fast forward to this weekend.  I decided to see if the spoolgun could be made to work on the was either that or convince my wife that I need to purchase the Mig140.  

The adaptation was suprisingly simple.  Obviously, unplug the welder before doing anything.

First, remove the cover of the welder by removing all the hex head screws.  The cover will NOT come completely off the welder because of the wiring harness.  This is not an issue as you will have plenty of room to work unless you have hands like baseball mitts.

Second, remove the existing gun by disconnecting the trigger wires from the bulkhead separating the spool side of the welder to the circuitry side of the welder and then unscrewing the wingnut that holds the gun to the welder.  Remove the gun from the welder. 

Third, identify the trigger wires on the circutry side of the welder.  These are the wires that connect through the bulkhead from the circuitry side of the welder to the spool side of the welder.  These wires have 1/4 inch female spade terminals on them.  On my welder the wires are black and green.  Since the trigger is simply a normally open switch, polarity doesn't come into play with these wires.

Fourth, identify the wires going to the wire feed motor.  This is the motor that feeds the wire through the gun.  The motor is on the lower right of the welder if you are looking at the welder from the circuitry side with the front panel to the right.  On my welder, the wires are orange and purple with the orange wire being the positive wire.  Polarity here is important.  If you get the polarity wrong, the wire won't feed through the spool gun as the motor will be spinning backward.

Fifth, Cut the orange and purple wires going to the wire feed motor at a place where you can install 1/4 inch female spade terminals on the wires coming from the circuit board.  You may also want to install 1/4 inch male spade terminals on the ends coming from the motor so that you can easily reconnect the welder's motor if you decide to use the original gun instead of the spool gun at a later date.  You can also disconnect them from the motor, but that will take some extra disassembly of the welder because of the location of the terminals on the motor.

Sixth, take 4, 12 inch long pieces of 18 gauge wire and install 1/4 inch male spade terminals on 1 end of each wire.  Use different colors if possible as it will make things simpler to connect later.

Seventh, feed the wires through the front panel and connect 1 wire to each of the wires you disconnected, green, orange, and purple.

Eighth, disassmble the 4 pin connector on the spool gun and identify the wires in the connector.  There will be a yellow, a green, a red, and a white wire in the connector. 

Ninth, connect the wires from the welder to the wires from the gun as follows, (welder/gun)...
black to yellow, green to green, orange to red, purple to white.

I used the red crimp style butt connectors to make the connections at the plug on the spool gun.  I trimmed the insulation from the end I was connecting to the connector on the spool gun and crimped them slightly so that they would fit the pins on the spool gun's connector.

Tenth, reassemble the connector on the spool gun.  Tape any exposed connections to prevent short circuits.

Eleventh, install the spool gun in the welder and tighten the wingnut.

Twelfth, reinstall the cover and test it to make sure all your connections are good.  DO NOT PLUG IN THE WELDER UNTIL THE COVER IS REINSTALLED OR YOU WILL SEE SPARKS AND AT BEST, BLOW THE CIRCUIT BREAKER.

You are now ready to use your new spool gun with the Real Gear Mig135.
Everything is reversable so that you can disconnect the spool gun and revert to the original gun that came with the Mig135.  I will be purchasing the correct 4 pin socket and a 4 pin plug for the original gun, along with a DPDT switch, so that I can make the appropriate connections permanently attached to the welder and then swap between the spool gun and the regular gun without having to take off the cover.

I hope that this helps with the versatility of your welder.

Warning, Verify the wire colors on your welder before making the modification.  The spool gun book specifies the wiring, but the Mig135's book does NOT, so I had to trace the wiring and note the colors.  I can't be sure that the Chinese company that made the welder held to any wiring color code when they made these welders.