Thanks.
So anyway, I'd heard the MX5 wiring is a nightmare, there's all sorts of weird stuff about switched earths that I didn't understand, and others like the fact you need to keep a dimmer switch in the loom otherwise the fuel pump doesn't work (exaggerated for effect, i think).
However the standard loom is huge and heavy, especially with my donor being a fully specced Sport version, so it had wiring for heated seats, powered mirrors, rear screen, electric aeriel, etc that just won't get used.
So, in for a penny and all that i went to a company called Stafford Vehicle Components who do a modular loom for the car side of things. So for the best part of £300 I ordered their front engined modular loom and then hit Amazon for some wiring tools, waterproof connectors, multimeter, etc and set to learning stuff.
First off i laid out the new loom and went around it checking what wiring went from where to where and identifying the various branches, disappointingly they weren't labelled, and though it should have been a quick job working them out, there were a couple of errors on the wiring guide they sent...
The cluster of fuse boxes and relays in the bottom left were a new thing to learn about, but i got my head round it, it's just like programming little VBA routines with IF statements given the way my mind works.
At the same time i started to unpick how the standard wiring worked using the Haynes manual and the internet to teach myself to read the diagrams and then physically going through and unpicking the standard loom. I didn't need to do that for the build as such, but that's the way i learn, rip things apart and understand the concepts in practical situations.
Eventually, the loom looked like this.
Plus another couple of piles for the rear loom and dash loom, above is basically just the heavy electrical work, lights, seats, heated window etc.
So more confident i knew where i was going, i started making up the waterproof quick connects, basically i want to be able to remove any body or ancillaries easily, so for example the rear fuel tank shell will have lights mounted, so i can quickly disconnect them from the main frame where the loom will be routed.
Still need to work on my crimping..but getting there and the connections have continuity so all good so far.
The rear lights, indicators, reverse and fog lights all good to go.
So then it was downstairs to the garage and start putting theory into practice.
First was laying it all out and then connecting it up to the main engine loom and fusebox. I'm hoping like hell that i can just leave the engine side of things, it's running a custom MS3 ECU with sensors for IAT, wideband, etc and was wired in by a local MX5 race team when they supercharged it, so I'm hoping to not have to unpick that.
Again, a little bit of research on the way the battery and earths need to be set up and i got that sorted, then i wired in the steering column controls and tested the lights and got nothing. At this point i realised that the MX5 lighting system works on switched earths, whereas the new loom needs switched positive. Not a problem, after a bit of head scratching I just provided a live feed to the earth in the lighting switch and then the switch effectively gave me a switched positive to use. This does pose 2 problems, i think i'm sending too much juice into the switch now (and don't fancy ripping the column apart to fit more suitable wiring) and because i need a permanent live for the side lights, i've used a permanent live. However IVA says that your main and dip lights must be ignition switched.
So, although i'm yet to do it, what I'm going to do is take a low voltage permanent live into the switch, and then output that to a little relay set up for the side and main lights that will take the required power where it needs to go depending on light switch and ignition switch positions.
However, while keeping a close eye on things, i had to test the progress and to see if my workaround had worked.
