Electrical
One way to think of a modern cars electrical system is to break it into 3 parts, the engine harness, the car harness, and the power distribution system. The engine harness connects all the various engine related sensors and controls to the ECU, which is the main computer which controls the engine. The car harness talks to electrical components in the car like lights, doors, switches, climate control, radio, etc. The power distribution makes power available via the battery/alternator to everyone. So in a swap we must make some connections from the engine harness/ECU to power and various systems on the car that the ECU needs to know about like ignition state, oxygen sensor output voltage, as well as allowing the ECU to control or send signals out on the car harness like the instrument panel, fuel pump control, and a few other things. In the grand scheme of things it is really not that hard, conceptually, it's just figuring out those dang wiring diagrams and how to match them up and were to get at things. A nice summary of the CRX-KSwap wiring interface is given by Hondata here. They also have a lot of other important and useful information here. So you can wire it yourself with some patience or you can buy any one of a number of conversion kits that will make the job simpler. But don't be deceived, they will all require that you do some hand wiring although they certainly make life easier.
The ECU is the other thing you will have to deal with. The stock ECU is not swap friendly as some of the systems the ECU uses are not present, including, if you have a USDM engine, the ignition immobilizer, which must be disabled. The solution for this is to reprogram the ECU (hey, its just a computer) and the people at Hondata make an elegant solution in the form of the K-Pro ECU. The K-Pro is simply your stock ECU which has been modified with a piggy back board which allows easy access to virtually every feature in the ECU that controls the engine. The piggy back board provides a USB interface which can connect to a Windows based PC. Hondata provides a software package running on the PC (Hondata KManager) which provides a comprehensive and easy-to-use interface for reprogramming the ECU. For example, to disable the immobilzer you just clear the menu option to for the immoblizer. It also has special support for controlling things like nitrous injection, boost control, and you name it. In addition, and perhaps most importantly, it allows you, or an experienced tuner, to tune the fuel, ignition and cam angle tables to optimize your engines performance and keep everything within safe limits. Hondata provides you with lots of base maps for many different engine/header/intake combinations to ease the tuning of your specific setup. This is not a cheap setup, it runs about $1000 and you need to supply your existing ECU. But if you think of the R&D that went into it, including the software development, it is a pretty fair deal.
Finally, once everything is up and running, bring your car to a reputable shop to dyno-tune your engine. It may cost a couple of hundred bucks, but considering the investment in the swap, it is chicken feed. It also insures 1) your engine is running under safe conditions and 2) you engine is running to it's maximum potential. Just check out my before and after tunes on the dyno.
Power distribution and grounding
In our setup we decided to relocate the battery and the main fuse box which both normally sit in the engine compartment. I thought this would make for a cleaner setup. The plan was to pull the main fuse box into the passenger compartment and mount it on the firewall behind the glove box, since the AC was gone there is now lots of room there. I borrowed Brian Collier's method of battery relocation which I thought was pretty elegant. He uses a small sealed drycell Odyssey battery (PC680) and mounts it behind the passenger seat in the existing storage bin. Since this is a sealed battery, it does not emit fumes and is safe to mount inside the passenger compartment. In addition it can be mounted on its side and is about half the size and weight of the stock battery. Despite the small size, it has plenty of power to crank the motor and run the electricals and to date I have had no problems. I do not generally run the car in the winters here, so I do not have any experience with the batteries cold weather performance.
Relocating the battery requires paying careful attention to a couple of things. First is your grounding and power cables must compensate for the extended distance from your high (and low) current systems. Second, you are now running unfused high current primary power through your passenger compartment and the danger of a short anywhere in the system could be disastrous. People fail to realize how much power is in a car battery, you can literally weld with it. The solution is taking great care in routing and protection of the battery cable(s) and finally you should fuse the battery so that if there is a short, your fuse blows instead of your car blowing up. We wound up using fuses and connectors design for high powered stereos in cars, they are affordable and easily interface with heavy battery cables. We used an ANL type fuse holder from Rockford-Fosgate, it can use fuses up to 500Amps, we found that for our application 150amps works well (don't forget to cary spares!). The fuse gets mounted as close to the positive terminal as possible, you can see this in the Pics. We used 2 gauge wire for the cabling, which is probably overkill. The cable was sheathed in heavy polypropylene spiral wire wrap for further protection and run under the passenger door sill to a power distribution block (again Rockford-Fosgate) under the dash from where one run goes to the main fuse box and the other to the starter. Pay attention to the routing and secure everything carefully. Finally, some brackets were fabricated to mount the main fuse box behind the glove box and the main electrical harness was pulled into the cabin and wired up. You can see how it all looks below.
Grounding is critical, a poor ground can reek havoc. Our battery ground goes to what I think was a rear seat belt mount point on the chassis next to the battery. Clean the contact points to the chassis to bare metal and use copper or brass fittings. The engine ground is important as well and the folks at Hondata discuss this in detail. I have large grounding wire on the transmission, engine manifold, cylinder head, starter and alternator. They all connect together to a common ground on the front right side of the chassis along with the electrical ground for the lighting. Hondata also recommends not relocating the battery for a variety of reasons including a problem with charging. I disagree here and in my implementation I have had absolutely no problems. Also, don't forget to ground your radiator as the temperature sensor needs a ground.
ECU and wiring
Some additional brackets were made to mount the K ECU into the existing CRX ECU location under the passenger foot plate which is now directly below the newly relocated main fuse box. We wound up using an adapter harness from Rywire to get it all hooked up. You still need to splice in a number of wires by hand but it does make it easier. We also found things were not quite right in the harness for the ELD and Fan control. But we traced it through and corrected those problems. It's not too bad, the hard part is just familiarizing yourself with the wiring diagrams but once you do you can troubleshoot just about anything.
Instrument Cluster
One issue with this swap is that the CRX instrument cluster uses a mechanical driven speedo and the K is electronic. The solution is swap the cluster for one from a CRX JDM type SiR or adapt an EG panel. I also had the issue that my cluster was for an automatic, and had a lot of idiot lights specific for the automatic which was esthetically displeasing to me. So I found an SiR type cluster on EBay. Of course the wiring is very different so you need to do a lot of rewiring as you can see in the Pics below. Unfortunately the original resources on the web I found seem to have disappeared so you might want to do some googling. It works great and even all the idiot lights are functional. One problem I did have was the illumination for the panel was not very bright, so we replaced all the bulbs with LED type bulbs, looks cool too.
