Gremlins - Washers, High-Beam, Boot Release and Dome Light Don't Work (Intermittent)

Technical Area Electrics & ICE
1
  1. My model of MX-5 is: 2017 ND RF
  2. I’m based near: Manchester
  3. I’m looking for technical help or recommendations on: Electrical Funz! :upside_down_face:

Hello, I have been having some “fun” lately with an intermittent problem on my ND and was hoping someone might be able to provide some advice.

I believe original symptom I encountered was the boot opens when starting the car. When this occurred I had not been in the boot before starting the car and the key was in the center cubby so the button wasn’t pressed.
Sounds like the opposite of this: Mx5 ND, Boot opens when turning off engine (Edit)

I have since had more developments which are a little more worrying, namely 4 symptoms that occur together:

  • Boot buttons don’t work
  • Interior (dome) light doesn’t respond to doors/turning the car off
    • The light can be turned on using the switch so the bulb is fine
  • Washer doesn’t work
    • Wipers are fine
    • Washer bottle is brimmed
    • Fuse is fine
  • High Beam doesn’t work
    • Dash displays indicator
    • Fuses are fine

The really annoying part is that it is intermittent and sometimes just works!! So I know that everything works but at some point during a drive they will just stop functioning and even when I stop > car off > car on, it doesn’t always fix it.

Recent scenario: Opened boot, deposited items, closed boot, started car, back to boot (forgot something), couldn’t get in, drove to Tesco, still can’t get in, test washer, doesn’t work, back from Tesco, check fuses, fine, notice interior light doesn’t work, drive ~45 mins, washers still don’t work, boot works on arrival as do washers and interior light.
Few hours later, test everything, all good, drive for 10 minutes, high-beam dies, washer no longer works, interior light has gone too, finish 45 minutes drive, tinker until everything works (wiggle interior fuse box, check fuses etc. all good) and I can finally access boot.

I have looked and believe they are all linked to the ESU but that seems fine and when everything works it all just works!
Haven’t had a chance to get a decent code reader plugged in to see if there are any errors.
I have fully disconnected and then reconnected the battery, it behaved for a bit upon reconnection and starting but when the car was next started to was all kaput again.

Hopefully someone has some thoughts as I am starting to pull my hair out over this as it is so frustrating and infuriating :rage:

Might be worthing noting…I have previously fired my main fuse which also killed the washer fuse (but after replacing it was fine for a good few months) and I have been caught in torrential rain with the roof down but I tried to do my best in drying everything out thoroughly

2

Have a look here Main Menu - MX5 Manual | Mazda MX5 (Mk4) 2015+ and see if there is any commonality between your problems.

If it were a Mk3 then damp in the fuse box would be a favourite and as you say you have had rain inside may be a good look at the passenger nearside footwell would be in order. It is easy to remove the plastic door sill and then the trim so you can have a good look round.
:heart:

3

Hi Malc, I have already been through the whole manual and the only commonality I can find is the ESU but they are on different plugs and I have inspected that and the interior fuse box and not found any evidence of water annoyingly.

4

Why was the main fuse fried? And was the cause attended to?

5

I can’t be exact here but at the bottom of the windscreen behind the panel where a glove box would be on the passenger side there is a connector that can get water in it. Condensation from the windscreen can run into it from memory. Probably worth checking connectors it that area for signs of water ingress.

6

Main fuse was fried down the starter/alternator side when jump starting
Having spoken to Rodders it isn’t that uncommon

7

My guess would be a bad earth as I know your car has done a few miles……

8

May have just ticked over 97k :see_no_evil:
Had a more thorough check of the connections in the passenger footwell today, everything seems good, no evidence of water ingress etc. and since then it has also been fine… :crossed_fingers:

9

Replaced the ESU today and everything appears to be back to normal :tada: