Been taking all the redundant wiring out of the Honda loom to just leave the engine side, however I think I may off accidentally removed part of a wire.

The wire is brown and goes from pin D4 (SCS) to the diagnostic plug, however it is also spliced to split off elsewhere. It is this split which I appear to have cut and removed, where should it go to?

Other than that progress has started again, subframe finished, roll cage in. I will update with pics on my build thread when I get the chance.

I'd say to get one of them maintenance manuals on disk off ebay for a couple of quid - it should give you all the wiring diagrams.

Got one, but the wiring diagrams aren't as detailed as you would think. Got a couple of other diagrams, but believe they are for the earlier OBD0 wiring of the B16A1 and therefore don't have the diagnositc plug as the fault was shown through an LED directly attached to the ECU.

Managed to trace and sort all the other wiring its just this one wire, don't even remember cutting it (particularly as it is attached to the ECU and plug) but it definitely doesn't go anywhere at present.

You only need the one wire coming from the ecu, from memory its brown on my car too, it goes to pin D4, i use to leave this wire taped in the loom, ready to be earthed out if needed to the chassis to operate the diagnostics it does not need to be connected to anything, at the minute with my Hondata it activates my full throttle shift.

the only tim eyou need it it too read error codes and to set the ignition timing

WEST

Cheers for that West, had another look through the wiring. That brown wire is on a plug that also has a white/green wire going to pin D22 (sensor ground), there is another plug next to it, again to D22 but also a light blue wire going to D7 (diagnostic data link). Which of those 2 plugs do I short across to get the blink codes out of the MIL?

I've got a similar plug near where the loom passes through the bulkhead to the offside of the engine, it has a white/blue wire coming from the underdash fusebox and a green/red wire going to the offside of the engine. What is that plug for? Is it diagnostics again, as the loom where it attaches to the engine has the green/red wire with a detachable plug to the black earth wire. There is also a blue wire that is capped off, which I'm guessing is the tacho feed to an external sensor.