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Got an early UMC from a friend with visible melted plastic between the connector and the 14-50 adapter. During charging the AMPs would drop to 20 and clearly was not safe to continue using it that way.

By the way, here is a disclaimer:
I shall not be held responsible for any damage to hardware or persons that may arise from following the post below. Use this post and the information herein at your own risk. What I describe here is a modifications to electrical and electronic device. Do not attempt to follow anything listed below unless you are competent to do so, as you could get a serious electric shock or even electrocution if you do not know what you are doing. If you are in any doubt about your ability to perform a certain task, then get someone else who is competent to do it for you. Make sure any item you are working on is powered off and unplugged from the mains before starting work. I repeat, use this post and the information herein at your own risk.

Many thanks to MPT for his advice.

Here is the patient...

Melted%20Connector.jpg

Instead of throwing it away, I decided to cut the melted connector away and replace it with a Camco 50 AMP replacement plug ($15 at Amazon).
61NG-3OFovL._SL1266_.jpg

After having cut the connector off, you are presented with the following:
2 Red wires
2 Black wires
1 Green/Yellow wire
1 tiny purple or maroon wire
1 tiny blue wire

The Red and the Black wires are the two hots and go on the two opposing blades while the green is the Ground and goes to the round prong.
There is no Neutral in the UMC so the bottom blade does not get connected to anything.

Now for the tiny wires; the blue is not needed but the purple/maroon wire is needed to signal the Amperage required.
This is the table: (Courtesy of various TMC members)
40 amps - 9.08k ohms
24 amps - 33.16k ohms
16 amps - 75k ohms
12 amps - 140k ohms

Since the gaps between steps are fairly large I figured that a 1ok ohms resistor would do and to be safe I looked for the highest wattage possible at Radio Shack and came up with this pack of 5
Resistor.jpg

They all measured about 9.7k ohms so I picked the closest to the desired value of 9.08k ohms

I simply twisted the resistor in line between Ground and the purple and wrap it with electrical tape but it would't be a bad idea to solder it.
Final%20Assembly.jpg


Once plugged in green light goes on (otherwise you'll get a red one)

Final%20Product.jpg


Charging well at 40 AMP 231V
40AMP.png
 

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How timely!
Last week my car started refusing to charge from my UMC and after reading this post I checked the plug end and it had the exact same issue with the adapter pins melting. This fix worked for me in 30 minutes incl cleanup. Thanks for posting it!
 
How timely!
Last week my car started refusing to charge from my UMC and after reading this post I checked the plug end and it had the exact same issue with the adapter pins melting. This fix worked for me in 30 minutes incl cleanup. Thanks for posting it!

Is your car out of warranty? Otherwise I think Tesla would have replaced your UMC.
 
Is your car out of warranty? Otherwise I think Tesla would have replaced your UMC.

Nope but I'd expect Tesla would take exception to the J1772 plug I put on the other end so I could charge both our MS and Fiat 500e (until our M3 arrives). Interestingly we installed a HPWC a year ago so this UMC was only used for 30A charging of the Fiat for the past year and still overheated at the plug end.
 
Got an early UMC from a friend with visible melted plastic between the connector and the 14-50 adapter. During charging the AMPs would drop to 20 and clearly was not safe to continue using it that way.

By the way, here is a disclaimer:
I shall not be held responsible for any damage to hardware or persons that may arise from following the post below. Use this post and the information herein at your own risk. What I describe here is a modifications to electrical and electronic device. Do not attempt to follow anything listed below unless you are competent to do so, as you could get a serious electric shock or even electrocution if you do not know what you are doing. If you are in any doubt about your ability to perform a certain task, then get someone else who is competent to do it for you. Make sure any item you are working on is powered off and unplugged from the mains before starting work. I repeat, use this post and the information herein at your own risk.

Many thanks to MPT for his advice.

Here is the patient...

Melted%20Connector.jpg

Instead of throwing it away, I decided to cut the melted connector away and replace it with a Camco 50 AMP replacement plug ($15 at Amazon).
61NG-3OFovL._SL1266_.jpg

After having cut the connector off, you are presented with the following:
2 Red wires
2 Black wires
1 Green/Yellow wire
1 tiny purple or maroon wire
1 tiny blue wire

The Red and the Black wires are the two hots and go on the two opposing blades while the green is the Ground and goes to the round prong.
There is no Neutral in the UMC so the bottom blade does not get connected to anything.

Now for the tiny wires; the blue is not needed but the purple/maroon wire is needed to signal the Amperage required.
This is the table: (Courtesy of various TMC members)
40 amps - 9.08k ohms
24 amps - 33.16k ohms
16 amps - 75k ohms
12 amps - 140k ohms

Since the gaps between steps are fairly large I figured that a 1ok ohms resistor would do and to be safe I looked for the highest wattage possible at Radio Shack and came up with this pack of 5
Resistor.jpg

They all measured about 9.7k ohms so I picked the closest to the desired value of 9.08k ohms

I simply twisted the resistor in line between Ground and the purple and wrap it with electrical tape but it would't be a bad idea to solder it.
Final%20Assembly.jpg


Once plugged in green light goes on (otherwise you'll get a red one)

Final%20Product.jpg


Charging well at 40 AMP 231V
40AMP.png
Awesome guide! I'm getting ready to try to turn 2 gen 1 UMCs into DIY corded wall connectors. Would really help to be able to see the rest of the photos, do you think you could reply with them? I know it's been a long time but thought I'd ask.
 
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My apologies. I was thinking / typing out loud. What I should have asked is if you know why the blue wire was ever included. Seems odd to run an unnecessary line. Guide was very thorough, appreciate it.
No worries, I hope it works out for you. I really don't know what the blue one was for. Post some pictures of your mod and final result.
 
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No worries, I hope it works out for you. I really don't know what the blue one was for. Post some pictures of your mod and final result.
Done! Replaced the plug on two Gen 1 UMCs today and they're both working wonderfully!
Sharing some details just in case someone else wants the info:

I decided to use a different plug than the one above. The plug was designed for a 1" cord diameter, so I used a small piece of dishwasher drain hose which allowed 1/16th" gap between the cord and the plug bushing. While not perfect, I think the result was clean enough and the cord is held quite securely.

I used a short piece of insulated wire from an old extension cord and soldered it along with the ground wire. I braided the stranded pairs together first then soldered. I used heat shrink to hold the pair together.

I also applied solder to each of the tips of the black and red wires before screwing them into the prongs to increase conductivity.

I picked a resistor at 9.83 Ohm and soldered it to the purple wire and the other end to the extra wire added to the ground wire. Used heat shrink to shield the ends. The plug has plenty of room along the edges to tuck the resistor out of the way of the prongs.

Not wanting to cut any of the four other small wires, I used heat shrink to cover them and tucked them under the wires and prongs in the plug. I'm sure they could just be cut but I wasn't sure so I kept them but shielded them.

Please note: if you use this same plug the holes holding the three thin screws are much much too tight. Pray to whatever God you believe in for strength backing them out. I used a 7/64th" drill bit to expand the screw holes before reassembly and it helped while still holding fast.

Parts used:

Parkworld 14-50p Replacement Plug:

1" inner diameter 5/8th" inner diameter dishwasher drain hose:

10k Ohm resistors:
 

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