NC Heated Seat Fault?

  1. My model of MX-5 is: __MX5 NC 2012
  2. I’m based near: __ East Midlands
  3. I’m looking for technical help or recommendations on: __Heated Seat staying on

Hi, my drivers heated seat has started staying on permanently. I have just took the heating level control dial off thinking I might be able to swap it around to test it but the fitting is handed so you can’t. It also still comes on with the switch removed.

Has anyone experienced this?

I guess I can pull the fuse but would be good to understand what would need replacing so I can fix it. I can’t understand what else it might be if it’s not the control dial.


What’s your VIN?

Hi Robbie,

It is


I’ll have a look at the wiring diagram and give you some pointers. Won’t be today though :beer:

Thanks, appreciate that.

The first check would be to remove the 20Amp seat warmer fuse and check that the seat warmer turns off, I assume that it does and only the driver’s side seat warmer is on constantly.

As you say that the warmer stays on even with the switch disconnected, then I’d first investigate a short to ground between the Green wire from the connector under the seat to where is arrives at the heated seat plug. Take care working around the under seat connector as there are air bag wires in it. If that checks out OK, I’d suspect a fault with the seat warmer itself.

Is there a chance that someone has been working in the area of the radio and trapped/cut the Green wire for the seat heater?

Hi, yes I have removed the fuse and it stops working.

It is only the drivers seat that stays on.

No one has been working on the car, it just never turned off one day, has been working fine for the last two years since I bought the car.

Can I deactivate the air bag wiring to allow me to investigate?

Proper way is to remove the 12 volt negative battery terminal and wait 10 minutes before working in that area. If you’re poking about with a multimeter in that area take extreme car not to probe an airbag wire by mistake. The connectors are usually yellow. To be honest, if no one has disturbed the wiring I’d be more inclined to suspect a faulty seat heater.

Ok, thanks for the advice. I will find some time to carefully have a look in case something obvious has happened. I assume that the faulty heater unit is a case of changing the seat or is it a seperate unit?

Just a thought - but if the heater unit is staying on when the switch is unplugged - I would be looking at the wiring or the relays - the heater element is clearly working.
The issue is - it is getting power to it somehow when you don’t want it to.

The heating elements are permanent live and the ground is switched by the seat heater control module. It must be an earth side or heater fault.


Didn’t look into what’s available separately. If you’re buying new then I would guess that you could get the heater part separately (looks like it comes with the controller). If you’re buying used, probably not worth stripping the seat to get the heater parts out.

Of course!, been a while since I done anything to do with wiring. I will see what I can find

Thanks guys