I see this question a lot.
This is for if you have swapped a VTEC engine into your car (or done the mini-me swap), but don't want to have to use a whole new engine harness in order just for a couple VTEC wires to work.

Here's a write-up from HondaSwap:
This is something that I see come up, and sometimes people get confused by the written instructions, so here's one with pics. This can also be used for wiring just about anything you need, like a knock sensor, IABs, 02 sensor, whatever. I HIGHLY suggest have a manual with a wiring diagram and the pinouts, for your ECU, you don't want to screw up now that your motor's in right?

Ok, assuming you have a vtec motor in a non vtec car and you need to wire in vtec y0! here it is...

Our demonstrator model is a 95 CX with a OBD I B16A. So you have your motor in the car, and you are using XXXX engine harness, as long as you have the plugs (usually come with motors harness, even JDM, just remove the whole thing from sensor/solenoid, to canon plug from the harness)) you're good. First you need to run the wires...

BLU/BLK and GRN/YEL from here...



To the canon plugs (shock tower connectors)...



Now, if you are using the vtec harness there's no need to remove them as there should be nothing plugged into the connector on the other side (on a vtec car, such as a VX, or 92-93, this part is over, as it will have them already) the wires should match up to empty slots. But if there is something on the other side, simply remove them (vtec wires) to an empty slot with nothing on the otherside. For the cabin side of the canon plug, you need to get the pin from the canon plug, to the ECU (junkyard). you need to get enough pins from a junker to connect whatever you are connecting.

Anyway now you have the wires going from the vtec solenoid, to the canon plug and out the other side (note, I have both YEL/BLK, be smart and use different colors so you don't have to guess which is which at the ECU)...



Now, make sure the wire coming out of the cabin side of the canon plugs is long enough to go through the firewall, and to the ECU.

For the ECU connections same as the canon plugs, you need to acquire the pins. You can pull these out of a junker also. All the pins from the same generation are the same (there are two different sizes in each plug, you'll be using the smaller ones), and I was told that they are all the same from any model, and probably all generations, but I won't swear to it.

Here's how to remove the pins from the ECU...



If you want to take the time, you can pull the wire al the way from the ECU plug, to the canon plug, but I just splice a couple together, it saves a lot of time.

Here is what you should have...



The ECU slots on the non vtec models should have nothing in place, just a hole. At this point you should know where the pins go BLU/BLK (in the engine harness, maybe different if you used a different color wire) to D6, GRN/YEL (same as the other) to A4, so what are you waiting for, plug them in already...



Any time you need to splice wires together, I suggest soldering them when done, if you can't, at least use a good male/female plug, I like these... (soldering your wires...no, really, do it)



Now, you should have vtec y0!, drive around let your car warm up and then let it rip (provided you aren't still throwing a CEL code). If everything is kosher, bolt in your ECU, wrap everything up, and blend it into your harness for that nice clean look.

You can also by pass the canon plug, and run a hardwire all the way from sensor to ECU, this works to, but doesn't look as clean.

Here is some more wiring pics, to give you some ideas. In the first one, I am using a VX harness (5 wire o2) on a B16A (four wire o2) in a CX (1 wire o2) so I had some issues . Anyway, after figuring out what wires were what, I used my handy connectors and connected...



For the switched 12V, I used the plug full of YEL/BLKs on the driver side that goes to the main relay (thanks Poison), and spliced into one of the wires, then ran it to the o2 taping it into the harness once it was all connected, running right...



If anyone found a mistake, or has something to add feel free. I hope this can help someone that like me isn't real confident in their wiring abilities. All in all you are only limited by how much work you want to do. You can go for a quick get it going job, or undo your whole harness and rebuild it better than OEM.

A funny antidote that happened during this, so, my car even though it was a CX had a VX motor in it, so it was wired for vtec, sort of. Anyway there was no vtec kicking in, and I was throwing CEL 21, so I looked, and realized the guy that had swapped in the VX motor, had mix up the vtec wires, so I unplugged the canon plug and made sure what was where, and undid the wires, and switch the two of them right. Well, I get in the car and go to start it, and it's cranking, but nothing, like it has no fuel. So I was like "****" pull the codes. I get 6, 15, 21, 41, so I am thinking that switching the wires really screwed something up, so I go and re wire them like they were, and am looking at it, and then realize, duh, I didn't plug the canon plug back in :P , So I plug it in and get no codes, I was right, they were backwards, so I went for a cruise to make sure all CELs were gone, hammered it, and all is good.

(Original Post)

Mre information on VTEC wiring:
http://hybrid.honda-perf.org/tech/info.html#ECUpinout



(image from Clubeg6)

(D6 and A4 also apply to any D series VTEC engine that you will be using an OBD1 ECU with)
(Original image location)