Here is a question for those of you that are a lot smarter about electronics and/or electrical stuff than I am (which is probably the vast majority of you...
).
My '94 Honda VX is not OBDII, so no handy-dandy port to plug into so that I can access the plethora of wonderful engine stats coming and going...
Of course, I do have an ECU, so there is still a lot of that good info coming into the passenger compartment from the engine compartment... and a lot heading back out again too.
I'd like to tap into that information for a variety of things, not the least of which is to get the VSS and injector pulse width for the MPGuino... there are other things that (over time) I'd like to read or possibly even over-ride ... for instance, I might like to be able to stop the crank position sensor signal so that I have a "quick & easy" engine kill mechanism without having to switch off the ignition.
I am not really a fan of stripping the insulation off wires so that I can tap into the signal that way. Nor am I a fan of those 3M "guillotine" style connectors that provide a "brute force" approach to tapping into wiring... I've had too many of those cause the original wire to break at the tap point over time.
So my preference is to go to the wrecking yard, get myself an old ECU along with the section of the wiring that plugs into the ECU, pull the wiring harness socket out of the ECU, and build a "breakout box" that goes between the car's current wiring harness and the ECU.
I know that Honda has these in order to do diagnostics at the dealership... I also know that they would charge me ~$800
if I wanted to buy one from them.
So my question for you experts would be: What is the right way to build the circuits inside this box so that I can tap into the various signals (both analog and digital) without screwing up the signal that the ECU sends and receives? For instance, I recall a vague reference in college to the fact that introducing an alternative path to ground via some resistance could drop the voltage sensed by another portion of the circuit. I don't want to try to detect that voltage, and by doing so, screw up the voltage the ECU receives. Nor do I want to accidentally feed in a "digital" signal that confuses or overrides the ECU. And I certainly don't want to toast the ECU accidentally either. For some reason, I have a feeling that simply doing a "T" connection for each signal (digital and analog), I won't get that protection I'm looking for.
For the basic power and ground connections, I'd likely just pass those through the box without trying to break them out. Similarly, there are probably several signals I'm not even going to bother with and so will send straight through.
As an additional advantage, this approach would allow me to keep the original wiring "unmolested", which is another preference of mine.
Thank you in advance for your comments, suggestions, and thoughts.