I’ve followed what I think is the standard wiring procedure for modifying a Eunos to use the Genuine Mazda 5 pin switch:
1 (top left) - from (dimmable) dashboard-light
2 (top middle) - from ‘lights on’ switch (+12V, fused)
3 (top right) - to earth (used for ‘on’ indicator-light)
4 (bottom left) - to earth (used for (dimmable) dashboard light)
5 (bottom middle) - to fog light
Doing that means that my fog light works when I click the switch on and off. All good so far.
However, as per the newish MOT rules, I need my fog light switch to illuminate when I turn the fog light on and it isn’t working.
Have I done something wrong with the wiring?
I followed the Mellens wiring diagrams which I know are for Miata/Mx5 (and there can be subtle differences with Euniiiii) however the wiring did correspond to what I could see.
I’m getting 6v at all connections apart from Grounds which are 0.
MX-5 or Eunos never had a fog lamp switch with the tell tail in the switch. MX-5 had the tell tail on the instrument cluster and Eunos Roadster never had a rear fog lamp so you’re basically wiring in the tell tail from scratch. Which switch have you got? A switch from (IIRC) a 323F has the inbuilt tell tail light.
I think I have an original MX5 foglight switch with telltale light. It certainly has a telltale light as have just replaced it with a soldered on LED; bulb blown. Why can’t the telltale positive feed straight off the fog feed and the earth pair with the switch earth?
yes, that makes sense but I can’t see how this works?
Sure, the dimming function would work off that but where is the ‘foglight on’ relevant feed coming from? Surely there has to be a feed from the foglight feed wire for the light to come on with the foglight? Hoping for a clever explanation here that makes sense to me
I have read a few of the supposed explanations of this and my fuddly old brain is not making any sense of it. A simple foglight with no telltale transfers power from a load to the foglight feed with an earth in place, three wires in total. The telltale obviously needs an earth that can be shared? or…
Is the earth the switched bit for the telltale and the live permanent from the dimming circuit?
Seems way over the top for a foglight.
It all depends on what is inside the switch, and how the connections are brought to the pins.
If it is wired internally the same as the usual Front Fog switch (only three pins used), then On merely earths one end of the Fog relay coil and one end of the internal indicator, the other end of which is connected across the Fog relay coil to Headlight relay output for B+.
Alternatively the indicator contact could be wired to to the panel light dimmer output but ONLY IF a back-feed stopper diode is added in the switched line to the Fog relay coil.
However.
If the switch has two independent switched contacts connected to four used pins, ie one switch pair for the relay and another switch pair in series with the indicator, then it is “easy” (he said, tongue in cheek), just find appropriate wires in the loom.
Appreciate your intelligent comment as usual mate but the only way I can see this independent switch working as it should is with dash wiring that has the tell tale light anyway. The pins are all independent on this one.
I have it for sale but will remove for use on our 1991 Eunos with the dodgy packed out switch, that has probably worked fine for 20+ years:-). Will just connect up the fog feed to the telltale +ve and the two earths and expect it to do what is required.
Famous last words that I really should have hindsight but will report back honestly, hopefully tomorrow.
A bit fiddly adding the extra wires but works as it should now. I think the comments/write ups on this are more complicated than they should be. The standard foglight added to a Eunos just taps into a switched 12 volt feed. The switch just transfers the feed to the foglight bulb, no relay involved. The third wire is just a foglight bulb earth. Using a meter on these wires is confusing because there is continuity through the bulb. Telltale just needs to tap into the two wires that go to the foglight. I still cannot work out how the theory of the dimmer circuit picking up a foglight on scenario could ever work?
Not the case!! There is no specification at all regarding what a fog light tell-tale is. These are the rules:
When my fog light switch is depressed, facing the driver a slim side of the switch becomes visible. That side is covered with a sticker coloured in with highlighter. It has passed every year without comment.
There is only 3 of the switch pin connections that need connecting for the switch to illuminate when the rear light is on , the other two are dusk/,night illumination.
M-m
Hi, I have the exact same switch and the exact same problem. This is an original OEM Switch as far as I am aware, it came with the car. The connector that connects to it however only has 4 pins connected by wire. So I need to figure out where and how to use the last pin. Did you manage to figure it out?
