- My model of MX-5 is: __NB
- I’m based near: __Holmfirth
- I’m looking for technical help or recommendations on: __Heated rear view window.
Hi;
This weekend just gone I decided, having two fine days in a row, it was time to drop the roof for the last time this year and fit the hard top.
I think the wiring for the rear demister has had a bit of a bodge or two in its time but essentially this involves pulling a plug to the fold down roof and pushing on to the hardtop, two insulated flying leads.
The next day, whilst driving to work I discovered that the light on the dash wasn’t coming on and the window slowly became opaque.
Once I returned home I fumbled around in the dark checking fuses and eventually decided the issue might sorted by unwrapping that huge ball of insulation tape around the wiring where beneath the plug for the soft top that I’d unplugged the day before.
Oh dear! A bit of a look in the manual’s wiring diagram showed that, despite being fed from different fuses, both the control circuit and the demister itself all seem to work on a common ground. The wiring diagram showed a red and black cable as the +ve and a black cable as the -ve. This all made sense until the tape was removed showing both of the above along with a black cable with a white stripe. The negative from the window was connected across both of these. I lost my rag and hacked through the lot then stripped and put the lot into a wago which seemed to cure the problem.
What I really want to know is - what is the third cable (black and white? It was quite dark) for? It’s not there on the wiring diagram.
Thanks in advance of any reply.
Pete
Hi Peter, what issue are you having… Did it work previously?
I’ve done an edit, might explain better now?
Ah! Damn those balls of insulation tape! I think late NA and early NB are the same set up / very similar. We have an NA. Is the black & white wire go to a capacitor for radio interferance? Was the fuse okay in the boot? have read on another forum that there’s a 10amp in the mk1 and 15amp in the mk2 for heated screen and the10amp fuse if fitted can blow if screen on for a period of 10mins plus.
It’s quite a complex circuit for something that could be quite simple. The extra wire that your referring to is I suspect an earth jumper wire that means that the relay coil won’t find an earth without the HRW plug on the rear shelf (I1-03 in the diagram) being plugged in. If you have a B/W wire then you should also have the rear window defroster power cut switch that cuts the ground to the relay when the soft top is lowered. If you’re swapping the wires on the glass rather than using a separate loom for the HRW and plugging it in on the rear shelf, then the power cut switch will stop the HRW operating.
Does this diagram help at all?
That makes sense. I think I did something about a condenser.
Not aware of any fuses in the boot. Just a 10 amp in the interior dude box which does the rear screen and door mirrors.
Seems to working now.
It does, makes a bit of sense. There’s no switch on mine but the ball of black tape covering the dodgy scotchlock joints says quite a bit. Might need to think about a bit of a rewire come summer.
Thanks for that.
Glad to hear it’s back in working order Peter. We had to fit a fuse under the aerial in the boot for the heated screen and electric aerial. All the best
