My 2007 100 series did not come with a trailer hitch. I also didn't have it in the budget to add a custom aftermarket bumper/tire carrier/ladder just yet. I did need a trailer hitch attachment immediately so I bought an aftermarket hitch bar and attached it to the rear of the vehicle. Unfortunately mounting that aftermarket hitch bar required me to remove the mount for the 7-blade, round trailer wiring plug. Having other more important fires to put out I just let the plug hang down for over a year which required me to reach under the truck and find the dangling plug each time i wanted to connect a trailer. I only had 4 flat connectors on both my trailers at the time so i always had to use a round to 4-flat to 7-blade adapter when I needed to pull one of my trailers. As my trip to Yellowstone and Teton got closer and with plans to pull an enclosed trailer, I wanted to permanently mount a trailer wiring plug with both 4-flat and 7-blade connections. I did a cursory search for a write-up of how to use the OEM plug under the rear bumper to mount a new adapter and wasn't able to locate what I thought would be the best solution. Of course now that i did all this work, and made a write up of it i'm sure someone will post a link to a part on Amazon or AliExpress for $4.95 with FREE Shipping! I decided to make exactly what I wanted by taking the OEM plug on the vehicle, adapting it to the new aftermarket 7-blade/4-flat vehicle connector and mounting it to the rear of the vehicle.
Requirements:
1 - Use the Toyota OEM 7-pin gray plug on the vehicle side as the source for the power/light connections.
2 - The trailer connection will be a dual 7-blade/4-Flat connector.
3 - The wiring harness will be long enough to connect close to the trailer hitch and mount to the underside of the hitch bar AND hopefully be long enough to adapt to an aftermarket bumper/tire carrier (SLEE, BIOR, etc).
Definition of Terms:
OEMR = OEM Receptacle = The permanently wired square, plastic, gray 7-pin Toyota Male connector mounted on a bracket under the rear bumper.
OEMP = OEM Plug = The square, plastic, gray, 7-pin TOYOTA female connector which connects to the vehicle wiring harness under the bumper.
OEM7 = OEM 7-blade = The round, 7 blade, vehicle side connector which originally mounts under the bumper. It was stock on my vehicle.
OEMH = OEM harness = The entire Toyota-manufactured ~12" wiring harness from the OEMP to the OEM7
NEW74 = New 7-Blade 4-Flat Plug= New Vehicle side Hopkins Connector with 7-blade and 4-flat receptacle.
NEWH - New Harness = final assembly of the NEW74 to the OEMP with an 18" extension
Material
12 gauge stranded wire, at least 12 feet
3/8" or larger wire loom/tubing, 24" or more
Electrical tape, ½ roll
Hopkins 47185 Vehicle Multi-Tow Wiring Kit (7-Blade & 4-Flat)
Flux
Solder
Heat Shrink, 10-12 gauge should be fine
Cotton Balls
Rubbing Alcohol
Tools
Continuity tester or Voltmeter with the ability to continuity test wire connections
Exacto/Razor Knife
Wire cutters
Wire strippers
Soldering Iron
Zip ties
Removal
First, reach under the rear bumper and find the OEMH. I found it on the rear driver's side, almost directly under the driver's side tail light. The OEMP was connected to the OEMR, which was mounted on a bracket with another similar plug, which I believe goes to the brake lights (?), though I didn't check the wiring diagram. Disconnect the OEMP from the OEMR and unmount the OEMH from the truck by removing whatever fasteners are used on your vehicle. Take the entire OEMH inside to your soldering work bench.
Prep Work
Cut open the factory wiring loom by using your razor knife to cut the electrical tape and expose all 7 wires for the entire length of the OEMH. Using your wire cutters, cut all seven wires at about the half way point, or a little close to the OEM7. I wanted to leave enough wire on the OEM7 in case I even wanted to put it back on the truck or use it for another project. Use a cotton ball and rubbing alcohol to clean up the OEMP and electrical tape residue from the 7 wires. Strip 3/8" off the cut-end of each of the seven wires from the OEMP.
Cut 7 wires from your 12-gauge wire at a length of 18". I mixed up red and black wire. Doesn't matter which color. I would not go shorter than this but longer would be ok. I will stress that it is important that all 7 wires be exactly the same length. You will see why at a later step.
Strip 3/8" from both ends off all seven wires.
Cut one piece of 12 gauge wire at 12" long. Strip the first two inches and then pull 7 strands completely out of the wire. Cut them in half so you have 14 single strands of wire. Set them aside where you can reach them easily with one hand.
Cut the wires on the NEW74 to all be exactly the same length and strip 3/8" off each one. You will need to cut off the 4-flat connector on the wire end of the NEW74.
Now at this point you have a choice, you can choose to go the easy route and use butt-end crimp connectors or solder and heat shrink. I do not like to use butt-end connectors if I can avoid it. They look cheap, invite problems with connections wearing and disconnecting later with vibration. They are not water tight. They are bulky. I could keep going and going. If you want to do it once and do it right use solder and heat shrink. It will take longer and you need to have a good soldering iron or you won't be able to heat up the wire enough to get the solder to flow, etc. But a good soldering station is a lifetime investment and can be had for less than $100. There are also soldered butt splice connectors with built in heat shrink if you choose to go that route, but they average over $0.50 each, and they are not available at Walmart. Choose your method to splice.
The Soldered Butt Splice
Attach a large flat tip to your soldering iron and turn on the soldering iron to a fairly high temp.
There is more than once way to skin a cat when butt-end connecting wires with solder, but I think the best way is using the process I illustrate below.
Take one piece of your 18" 12 gauge extension wires and pick any wire on the OEMP.
Slightly fray the stripped wire on each connection to be made to make the individual strands come apart. Press the two bundles of wire strands together until they nest over the full length of the stripped wires. Press the "wild" wires back down into the bundle and make it round and neat again. If you let it go at this point the wires will simply slip off each other and you will have to do it again. So grab one of those 14 single strands of wire and then wrap it around your new bundle of nested wires in this new wire junction. This wrapping strand is what will hold this connection while you solder it. Make sure there are no wires sticking out in such a way as to cause a sharp point after you solder. Sharp points will puncture heat shrink and cause a very difficult to locate short. Take your time now and it will save you hours later.
Apply flux to the wire joint, clean the tip of your iron, and heavily solder the tip of the iron.
Completely Solder the joint until you see solder flowing into the stranded wire on each side of your nested connection.
Do this for all seven connections on the OEMP. At this stage it makes no difference which wires connect to anything. As long as you have seven 18" extensions soldered to the OEMP at the end of this process you are fine. We will sort out the labeling and correct wires at the next step.
Once the soldering is done you need to cut 7, 1.5" pieces of heat shrink for the OEMP connections.
Slide the heat shrink on and use a lighter to get it down to size and a water tight connection on each of the seven junctions.
At this point you should have 18" extensions soldered to each of the seven wires coming off the OEMP with heat shrink carefully applied so that no connection will puncture the heat shrink.
Now this is where you want to check, double check, and triple check to make sure you get this right. Using your continuity tester you must map the OEMP wire colors to the individual blade connectors on the OEM7. This practice is what I know as "ringing out the wires". My OEM7 did not have a wiring diagram on the cover. The NEW74 does and that is a standard configuration. So I tested the color of the wire on the OEM7, found the exact and only single corresponding blade on the OEM7 and used the NEW74 to label its function. So you need to compare your trucks wire colors coming off the back of the OEM7 and VERY carefully make a color coded list. I used the instruction insert in the NEW74 box and simply listed the OEM wire colors next to the NEW74 wire colors and functions. I've included a picture of my wiring labels though I will stress that this is potentially only particular to the later 100s and possibly even my particular VIN. Do your own due diligence.
Remember to slide your second set of heat shrink tubing peices on at this time. Also, note that you will possibly be connecting different gauges of wires (yet another reason to solder vs. crimp connectors) so one size of heat shrink may not be sufficient. In my case I slid on the standard heat shrink i used on the vehicle end of the wiring, then i slid on a smaller piece of heat shrink to the smaller wire. Do it in this order so that after soldering you put the small piece on first, followed by the larger piece to go over the shrunk smaller piece.
Once you have your heat shrink and you have correctly matched the colors of the wires on the OEMP/OEMP (they will be the same) to the correct wires on the NEW74 you can make the connections to the wires on the back of the NEW74. Using the same method above nest each connection and wrap it with a strand of wire. I would recommend that you ring the wire one final time before you solder each connection. Soldering in the manner is difficult to undo neatly. Once you solder the connection it will be difficult to desolder without removing some of the length of the wire which will prove problematic when it comes time to wrap up the NEWH with wire loom/tubing and electrical tape.
Do all seven connections and then apply heat shrink, again being mindfull not to create any sharp point which could puncture the heat shrink.
Once you have completed the heat shrink it's time to wrap our splices with electrical tape once to create an added layer of protection from shorts at the splice locations. I wrap each individual heat shrink location once or twice, then without cutting the tape, simply add another splice, and continuously wrap the splices together making sure there is at least one or more layers of electrical tape between each splice. Once completed you should have two fat (but NEAT) humps in your NEWH.
The final step is to add the wire loom tubing. Cut the tubing to the correct length. I began by wrapping electrical tape around the very ends of the wire right next to one of the connectors, then continuously wrapping the electrical tape I slide the tubing into place and wrapped the end with tape. I made my way down the tape with a continuous run of tape, tucking wires and the large bundles into the tubing along the way. This step is where it can get frustrating if all your wires weren't cut the same length. If the wires are uneven then you will get stiff humps (hehe) in the wire There were some gaps in the tubing where the bundles of splices were, but that's why i used tape the whole way.
And when you are done wrapping with the tape, voila! Your NEWH is complete and ready for reinstallation. Mount the NEW74 to your bumper using the best method for your situation. I simply used self tapping sheet metal screws to mount to the underside of my hitch bar. ONce that is complete, connect the OEMP on the vehicle end of your NEWH to the OEMR, and test it on your trailer.
Hope you find this useful, and if you do this extension it would be useful to others possibly if you could post your wiring colors and labels so the community can get an idea of wiring variations between years. I would also like to know if any of you with ustomer bumpers have been able to connect trailer wiring connectors to your bumper and if so could you post a picture? Do you think an 18" extension of the OEM wiring would give enough length to mount the NEWH to a custom bumper in a convenient location?
EDIT: There is a five picture limit per post so I will have to come back later and move the sections of the instructions to the posts below to match up with the appropriate pictures.
Requirements:
1 - Use the Toyota OEM 7-pin gray plug on the vehicle side as the source for the power/light connections.
2 - The trailer connection will be a dual 7-blade/4-Flat connector.
3 - The wiring harness will be long enough to connect close to the trailer hitch and mount to the underside of the hitch bar AND hopefully be long enough to adapt to an aftermarket bumper/tire carrier (SLEE, BIOR, etc).
Definition of Terms:
OEMR = OEM Receptacle = The permanently wired square, plastic, gray 7-pin Toyota Male connector mounted on a bracket under the rear bumper.
OEMP = OEM Plug = The square, plastic, gray, 7-pin TOYOTA female connector which connects to the vehicle wiring harness under the bumper.
OEM7 = OEM 7-blade = The round, 7 blade, vehicle side connector which originally mounts under the bumper. It was stock on my vehicle.
OEMH = OEM harness = The entire Toyota-manufactured ~12" wiring harness from the OEMP to the OEM7
NEW74 = New 7-Blade 4-Flat Plug= New Vehicle side Hopkins Connector with 7-blade and 4-flat receptacle.
NEWH - New Harness = final assembly of the NEW74 to the OEMP with an 18" extension
Material
12 gauge stranded wire, at least 12 feet
3/8" or larger wire loom/tubing, 24" or more
Electrical tape, ½ roll
Hopkins 47185 Vehicle Multi-Tow Wiring Kit (7-Blade & 4-Flat)
Flux
Solder
Heat Shrink, 10-12 gauge should be fine
Cotton Balls
Rubbing Alcohol
Tools
Continuity tester or Voltmeter with the ability to continuity test wire connections
Exacto/Razor Knife
Wire cutters
Wire strippers
Soldering Iron
Zip ties
Removal
First, reach under the rear bumper and find the OEMH. I found it on the rear driver's side, almost directly under the driver's side tail light. The OEMP was connected to the OEMR, which was mounted on a bracket with another similar plug, which I believe goes to the brake lights (?), though I didn't check the wiring diagram. Disconnect the OEMP from the OEMR and unmount the OEMH from the truck by removing whatever fasteners are used on your vehicle. Take the entire OEMH inside to your soldering work bench.
Prep Work
Cut open the factory wiring loom by using your razor knife to cut the electrical tape and expose all 7 wires for the entire length of the OEMH. Using your wire cutters, cut all seven wires at about the half way point, or a little close to the OEM7. I wanted to leave enough wire on the OEM7 in case I even wanted to put it back on the truck or use it for another project. Use a cotton ball and rubbing alcohol to clean up the OEMP and electrical tape residue from the 7 wires. Strip 3/8" off the cut-end of each of the seven wires from the OEMP.
Cut 7 wires from your 12-gauge wire at a length of 18". I mixed up red and black wire. Doesn't matter which color. I would not go shorter than this but longer would be ok. I will stress that it is important that all 7 wires be exactly the same length. You will see why at a later step.
Strip 3/8" from both ends off all seven wires.
Cut one piece of 12 gauge wire at 12" long. Strip the first two inches and then pull 7 strands completely out of the wire. Cut them in half so you have 14 single strands of wire. Set them aside where you can reach them easily with one hand.
Cut the wires on the NEW74 to all be exactly the same length and strip 3/8" off each one. You will need to cut off the 4-flat connector on the wire end of the NEW74.
Now at this point you have a choice, you can choose to go the easy route and use butt-end crimp connectors or solder and heat shrink. I do not like to use butt-end connectors if I can avoid it. They look cheap, invite problems with connections wearing and disconnecting later with vibration. They are not water tight. They are bulky. I could keep going and going. If you want to do it once and do it right use solder and heat shrink. It will take longer and you need to have a good soldering iron or you won't be able to heat up the wire enough to get the solder to flow, etc. But a good soldering station is a lifetime investment and can be had for less than $100. There are also soldered butt splice connectors with built in heat shrink if you choose to go that route, but they average over $0.50 each, and they are not available at Walmart. Choose your method to splice.
The Soldered Butt Splice
Attach a large flat tip to your soldering iron and turn on the soldering iron to a fairly high temp.
There is more than once way to skin a cat when butt-end connecting wires with solder, but I think the best way is using the process I illustrate below.
Take one piece of your 18" 12 gauge extension wires and pick any wire on the OEMP.
Slightly fray the stripped wire on each connection to be made to make the individual strands come apart. Press the two bundles of wire strands together until they nest over the full length of the stripped wires. Press the "wild" wires back down into the bundle and make it round and neat again. If you let it go at this point the wires will simply slip off each other and you will have to do it again. So grab one of those 14 single strands of wire and then wrap it around your new bundle of nested wires in this new wire junction. This wrapping strand is what will hold this connection while you solder it. Make sure there are no wires sticking out in such a way as to cause a sharp point after you solder. Sharp points will puncture heat shrink and cause a very difficult to locate short. Take your time now and it will save you hours later.
Apply flux to the wire joint, clean the tip of your iron, and heavily solder the tip of the iron.
Completely Solder the joint until you see solder flowing into the stranded wire on each side of your nested connection.
Do this for all seven connections on the OEMP. At this stage it makes no difference which wires connect to anything. As long as you have seven 18" extensions soldered to the OEMP at the end of this process you are fine. We will sort out the labeling and correct wires at the next step.
Once the soldering is done you need to cut 7, 1.5" pieces of heat shrink for the OEMP connections.
Slide the heat shrink on and use a lighter to get it down to size and a water tight connection on each of the seven junctions.
At this point you should have 18" extensions soldered to each of the seven wires coming off the OEMP with heat shrink carefully applied so that no connection will puncture the heat shrink.
Now this is where you want to check, double check, and triple check to make sure you get this right. Using your continuity tester you must map the OEMP wire colors to the individual blade connectors on the OEM7. This practice is what I know as "ringing out the wires". My OEM7 did not have a wiring diagram on the cover. The NEW74 does and that is a standard configuration. So I tested the color of the wire on the OEM7, found the exact and only single corresponding blade on the OEM7 and used the NEW74 to label its function. So you need to compare your trucks wire colors coming off the back of the OEM7 and VERY carefully make a color coded list. I used the instruction insert in the NEW74 box and simply listed the OEM wire colors next to the NEW74 wire colors and functions. I've included a picture of my wiring labels though I will stress that this is potentially only particular to the later 100s and possibly even my particular VIN. Do your own due diligence.
Remember to slide your second set of heat shrink tubing peices on at this time. Also, note that you will possibly be connecting different gauges of wires (yet another reason to solder vs. crimp connectors) so one size of heat shrink may not be sufficient. In my case I slid on the standard heat shrink i used on the vehicle end of the wiring, then i slid on a smaller piece of heat shrink to the smaller wire. Do it in this order so that after soldering you put the small piece on first, followed by the larger piece to go over the shrunk smaller piece.
Once you have your heat shrink and you have correctly matched the colors of the wires on the OEMP/OEMP (they will be the same) to the correct wires on the NEW74 you can make the connections to the wires on the back of the NEW74. Using the same method above nest each connection and wrap it with a strand of wire. I would recommend that you ring the wire one final time before you solder each connection. Soldering in the manner is difficult to undo neatly. Once you solder the connection it will be difficult to desolder without removing some of the length of the wire which will prove problematic when it comes time to wrap up the NEWH with wire loom/tubing and electrical tape.
Do all seven connections and then apply heat shrink, again being mindfull not to create any sharp point which could puncture the heat shrink.
Once you have completed the heat shrink it's time to wrap our splices with electrical tape once to create an added layer of protection from shorts at the splice locations. I wrap each individual heat shrink location once or twice, then without cutting the tape, simply add another splice, and continuously wrap the splices together making sure there is at least one or more layers of electrical tape between each splice. Once completed you should have two fat (but NEAT) humps in your NEWH.
The final step is to add the wire loom tubing. Cut the tubing to the correct length. I began by wrapping electrical tape around the very ends of the wire right next to one of the connectors, then continuously wrapping the electrical tape I slide the tubing into place and wrapped the end with tape. I made my way down the tape with a continuous run of tape, tucking wires and the large bundles into the tubing along the way. This step is where it can get frustrating if all your wires weren't cut the same length. If the wires are uneven then you will get stiff humps (hehe) in the wire There were some gaps in the tubing where the bundles of splices were, but that's why i used tape the whole way.
And when you are done wrapping with the tape, voila! Your NEWH is complete and ready for reinstallation. Mount the NEW74 to your bumper using the best method for your situation. I simply used self tapping sheet metal screws to mount to the underside of my hitch bar. ONce that is complete, connect the OEMP on the vehicle end of your NEWH to the OEMR, and test it on your trailer.
Hope you find this useful, and if you do this extension it would be useful to others possibly if you could post your wiring colors and labels so the community can get an idea of wiring variations between years. I would also like to know if any of you with ustomer bumpers have been able to connect trailer wiring connectors to your bumper and if so could you post a picture? Do you think an 18" extension of the OEM wiring would give enough length to mount the NEWH to a custom bumper in a convenient location?
EDIT: There is a five picture limit per post so I will have to come back later and move the sections of the instructions to the posts below to match up with the appropriate pictures.
Last edited:
