ChrisC

sorry wrong end of the stick. Now disconnect your reverse light switch

Sorry re-read what you posted, both connections to the reverse light are earth with the bulb removed?

Fuse and switch?

Have you disconnected everything, if not the bulbs will show a low resistance reading with earth. It’s why I said disconnect the rear lights and the reverse light and the fuse, so we can start ruling stuff out

I guess that’s lead not led

I suspect the switch as well, maybe the loom got caught during engine install.

If you discount the rear light (both) and the reverses light, disconnect the switch, and test the two wires (green and green and brown) if either are earthed you have a loom problem. Discounting the lights and the fuse should isolate the wires.

Either my post at 21;21 or boss hog at 21;22 will work ( boss hogs will be easier )

Disconnecting the light will prevent false earth readings through the build filaments, after all the are very low resistance until they heat up.

Remove your brake light bulbs (or disconnect the rear lights) disconnect the reverse light and remove the fuse. Then test your G37 and GN137 wires, are they earth? If they are disconnect the reverse switch, if the wires are still earth, then the loom is the problem, if not then the switch it is.

G37 is the 12v supply (from the brake light switch / fuse box) B13 is earth if G37 or GN137 is earthed good bye fuse

Are your switch connections Green and Green Brown? If the are Green comes from the fuse supplying both brake switch and reverse switch, if the Green Brown wire goes to the reverse light. So if your switch wires are giving a good earth when reverse is selected then the switch is faulty.

Based on that information the switch is shorting to earth when reverse is engaged, which for me can only mean two things, fault switch or wrong connection, let’s hope it’s the latter because replacing the switch might be an engine out job on a Mazda box. Edit - maybe not if you work from underneath with a crows foot spanner

The bracket is screwed to the frame with three self tapping screws. If the bracket hasn't got a good earth, what about the screws? Assuming the screws have a good earth put a serated washer under one of the mounting screws to get the earth in the bracket and another under the eyelet to get the earth from the bracket to the eyelet.

Yes the LED rear numberplate light is new from August last year, and looks like the wire is pre attached, but it must be connected into the loom somewhere? https://caterhamparts.co.uk/rear-lights/6979-lampnumber-plateled-08-18.html?search_query=number+plate&results=118

As I suspected the wiring diagram I have shows an MFU, which controls the fan (via the ECU). The MFU isn’t fitted to our cars but it’s basically a relay unit, so it will have been replaced with a relay. Sorry I can’t help with which one :-(

Yep Jim is right brake light switch adjustment would be my starting point for brake lights not working, and I have seen confusion on blogs about which wires to connect for the reverse light switch on the Mazda box. Your going to need a multimeter to check the earth of the rear lights to resolve that brightness difference, and I bet the number plate light. As for the fan I will check the last published wiring diagrams, however I know they are a little out of date.

Its not uncommon to get electrical issues sorted in PBC, my ignition switch was wired incorrectly when the ignition was switched on. Obviously I assumed it was something I had done while wiring the starter, but it was the person that wired my ignition switch that got it wrong, and I had no wires at all going to the start button. Problem for you is its not going back to CC for PBC. As a side project I replaced all my fuses with light up units. A small LED is built into the fuse which lights up when its blown, very handy for that quick check under the dashboard.

Yer it’s very tight getting a 105c stat plumbed in a S3

I think the fan and light are unrelated.

I find the gauges are a guide and not accurate enough to base any diagnostics on, after all the sensor and it’s earth are in the submarine tube, not on the engine. The ECU temperature is the only real guide but you can’t get to that without easymap. My car reads about 10C above the ECU on the gauge. I also think there is probably nothing wrong, but that will depend on the thermostat fitted to your car? Any chance you could post a picture of it. If you look at the CC parts website you will see two Duratec thermostats the 82C or 105C, the 105C has much longer plastic hoses on the housing. The 105C stat is what expect to be fitted to your car, it was mine. Since mine was an early 360R the ECU was programed to switch the fan on at 95C and off at 93C, which meant the fan was running pointlessly because the stat had not opened and the bottom hose was cold. If you haven’t got that situation then I suspect you have no problem. If you are confident you have no got an air lock, wait for the bottom hose to get hot, I.e. the stat to open, then wait a bit more for the fan to come on. If your not confident on the air locks, get hold of a IR thermometer, test it on some boiling water in a pan, then let it run up to temperature checking with the IR thermometer.

Just think of the damage that salt is doing to the unprotected skin, and impossible to clean joins between skin and steel. Hate salt with a passion.

Just a quick looks at the CC parts site, looks like the bracing goes all the way to the top mounting hole, where as you original is only braced to the bottom hole, so looks like changes have been made. I may be wrong, but it looks like the recessed holes are because the design has changed to add more strength around the join, i.e. it doesn't look like a butt joint anymore.

I am in no doubt CC are responsible for components supplied to me, and since I fitted all the components supplied, am I at fault for not checking the quality of my Bilstein nearside rear shock? It was fault free during the build and IVA, but failed at 2500 miles, how could I have spotted that. How could collidog (or the builder of his car) test at 12:30pm + speeds? Main stream manufacture don't check the quality of every parts being fitted, they just test samples. And I am sure if a new suppler comes on stream supplying batter leads to CC they will check the components they are purchasing, but that doesn't stop a fault batch leaving the supplier and ending up in kits or on cars after an establish supplier has a problem. Not sure I checked the crimps (under the heat shrink) on my supplied battery leads. If you follow that logic, you would have to dismantle the loom to check all wire joins. It's easy to blame CC, and in a perfect world every part would have a full QC process with sign off, but how expensive do you think that would make cars? Imagine a world without Takata airbag recall style scandals.

Do you think they make the leads? If the car cranked and fired I would have thought the batter connections would have been fine, so that would not have been on the top of my list when checking for poor engine running problem. In my book finding that seemingly unrelated component failure is good work. Obviously some people like to blame CC for all faults, but the truth is our cars are made up of many components from many suppliers. I had three warranty claims during my cars first two years, gearbox, shock and calipers, each component was supplied to CC in a box and then supplied to me in good faith. If the component had been manufactured to spec then my cars would have been warranty claim free, but it wasn't. And before anyone says obviously CC cut suppliers margins to the limit, and this is the reason quality control is poor with parts suppliers, think of the buying power of CC, then think of the buying power of main stream car manufactures. I know Ford buys starter motors for about £10, the same starter motor on our Duratec cars, but try and replace our starter motors for that.