I have a JVC KW-M730bt installed now (into my Mk3 NC2), and there’s a weird problem. When I turn my headlights on, the stereo screen gets brighter. It’s meant to be the other way round - When I turn the headlights on, the screen should dim, to reflect that it doesn’t need to be so bright at night.
The adapter I’m using seems to be correct in the wiring it’s linked to, but I’m assuming that the MX5 signal on the illumination wire is backwards compared to what the stereo is expecting. Is there an easy fix for this? I have seen one or two other threads regarding the older MX5’s having reversed illumination signals, but nothing for the MK3. There only seems to be a single illumination wire (blue/white).
Anyone found a solution to this?
After looking at some wiring diagrams, the MX5 default wiring seems to have both a “TNS (+)” wire and an “Illumination (-)” wire. I’m not sure which wire the adapter I am using taps into though. Would it be as simple as swapping the adapter wire from one to the other?
Ah good, you’ve found the Mellens diagrams. They are mostly correct apart from some LHD to RHD differences.
The TNS+ wire is switched by the Tail/iNstruments/Sidelights relay, and applies power to the hot side of all the T and S lights, and via the ‘Illum’ fuse to the Instrument lights AND to the dimmer switch module (Instrument Cluster Illumination). The Illumination (-) wire is the earthy end of the Instrument lights, and is controlled by the dimmer which has a Pulse-Width-Modulated switch (microcomputer on the drawing). So the dimmer system is expecting to see both ends of each light bulb. This system is shared by a lot of cars.
In my car the only interior light normally on during daylight is the screen on the radio. When the sidelights are lit then the panel lights light and the radio dims and all are controlled by the car’s dimmer - as one might expect.
However there is another system widely used by some other car manufacturers where the PWM switch is in the hot feed to the instrument bulbs and the earthy end of all the lights is hard ground.
Most radios are aware of both systems and just need the appropriate input pin selected for the system in use.
Here you might have to make a choice, and it depends on if the radio supports two option pins as suggested above for external dimmers, or just one for lights on.
You might be able to connect the Grey/Red Illumination (-) wire to a pin looking for an ‘earthy dimmer’ wire if the radio supports an external dimmer signal. If not then alternatively you might have to use the Red/Blue TNS+ signal and hope the radio can do its own dimming thing from its internal menus when told about the lights being on.
I’m afraid this is all very general, and I don’t know the connectivity detail of your particular radio, nor the adapter harness you’ve been given for it. Fortunately the MX5 is still very simple.
Thats the PDF instructions for the stereo I have, but the wiring instructions only show “A-6 = Orange/White = Dimmer”. The stereo menus for the dimmer control have three options: ON, OFF, and SYNC, where SYNC is the one that changes the dimmer depending on what the car lights are doing.
Dimmer ON means the screen is bright, Dimmer OFF means the screen is dim… which is weirdly backwards to me as well but its JVC so who knows.
At the moment the screen is going bright when the lights are on, which is obviously backwards.
That’s the wiring adapter I’m using, which as far as I can tell is the same as all the other MX5 adapters (connects2, etc) so I assume they all link to the same wire.
I can’t find the wiring diagram for it though, so I’d have to remove the stereo from the dash to figure out which wire the loom is connecting to - the TNS or the Illumination.
However from your explanation I’m still none the wiser as to whether swapping that wire over will work or not, or end up burning out all the electronics in the car.
I’ve just had a quick look at the Kenwood manual, and I think you need to use the Red/Blue switched TNS+ wire connected to the Orange/White. If there is a problem the Illum fuse will pop. However I expect the Kenwood will have a high impedance input there and take almost no current at all.
Thanks, I’ll have to wait until I can remove the stereo to find out if thats where the cable is already plugged into or not. However if it is attached to the dimmer line, I will swap it over and see if it works. I’ll have to report back, though I dont know when i’ll get time to do it… either be tomorrow or saturday. I’ll report back though!
The orange/white illumination wire needs to be connected to a dedicated sidelight/dash pod wire that is not controlled by the dimmer.Are all the dash lights on the dimmer circuit? What about the light in the cigar/power socket? Is a sidelight fuse easily accessible in the cabin fusebox?
Pass on all fronts. No idea. I assume all the lights are on the dimmer circuit. I don’t think there;s anything obvious that I would be happy to splice into.
All the wires required are in the Mazda connector intended for the Mazda fitted radio. No other splicing is needed. Normally the Mazda (loom connector) to ISO socket (in new radio) adaptor harness is sufficient.
And in this case it seems to be OK apart from the dim function, choice of the one wire from two already there.
I mean yeh… all the wires are in the mazda connector, the problem seems to be that the voltage is inverted compared to what the head unit is expecting. Seeing as all aftermarket head units use a standard input for illumination, it would seem that Mazda use a different format.
But not sure why you’re saying splicing isnt necessary. In order to get the lighting working properly, at the very least I would need to cut a wire from the current loom adapter and splice it into a different wire/socket, in order to get the feed from a different wire. Plugging it into a different socket on the adapter is probably the tidiest option, but I’m not sure if the adpater will be that easy to dismantle.
I was in there today to fix my steering controls, and moving those wires around will involve removing the entire stereo from the dash again and starting from scratch at the very least. So I just fixed the steering controls and reassembled the dash. The illumination will have to just wait, at least until I get a solid answer on what will work.
The Mazda Red/Blue switched wire is there in the plug; IF SWITCHED ON, ie high, it tells the Mazda radio to listen to the dimmer (clever logic inside the radio) and the mark to space ratio on Mazda Grey/Red dimmer wire tells the Mazda radio how bright the bulb should be. The new JVC radio will respond to the Mazda Red/Blue switched wire going high with its own dim setting.
Ignore the Mazda Grey/Red dimmer wire, it only confused the radio.
Yeh but I think the stereo is already recieving this signal from the Grey/Red wire, but the problem is that it is making the stereo brighter when the lights are on because the signal is the inverse of what the stereo is expecting…