- My model of MX-5 is: __nc2 MK3.5 2009 Sport Tech
- I’m based near: __Reading
- I’m looking for technical help or recommendations on: __Unable to open boot via fob or cabin switch. I do not hear any clicking sound from boot lock relays. My model doesn’t appear to have an over ride switch that is talked about in some threads - or if it does, I haven’t found it yet. I don’t see a fuse that is just for the boot - the central locking for the doors works fine. The only way to open the boot is currently via physically turning the key.
Has it ever worked? You are pressing the button for long enough aren’t you?
Hi Robbie, yes, it was working up until yesterday morning. When I tried to open the boot in the afternoon it didn’t work. I am holding onto the button long enough, I have two keys and the inside cabin button stopped working at the same time. Is there an override switch I haven’t found? Could it be one of the two relays under the lock? Is there a central locking module I may need to replace that controls the boot latch?
Always check plug-in relays if there is any doubt.
They are much easier to change than the lock solenoid!
If a pair have the same type number written on them, you could swap them over and see if the fault moves with the relay. eg. B110 is the type number in the relays below this boot lock, so these two could be swapped.
Contacts tend to age where they plug in as well as inside. Also the springs and pivots wear out.
Anything with moving parts (eg a relay) is more likely to fail than a solid state system, no matter how reliable they are intrinsically.
I will try swapping them over now as they are both B110, like yours. I just tried to see if I could measure voltage across the coils of both relays while pressing the boot remote button but I didn’t get any reading 
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I don’t think it can be the relays. I just tried swapping them around but no change. Both relays don’t recieve voltage when actuating the boot button and both relays read 100 ohms across their coils, so seem OK in that respect.
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That becomes more complicated.
Have you checked the ROOM fuse? That supplies the +12V to the pins E and C on the lower relay.
Grounding pin A will operate the relay and power the solenoid from pin D. (Don’t ground pin D!)
Hmm if no power on pin E then you have a PRHT and that module is acting up.
You lost me a bit there as I’m not sure where you get the pin lettering from and I’m not sure where to find the ROOM fuse. How do I get the relay pin out? Is it the lower relay that operates the boot solenoid? What is the upper relay for? However, on the lower relay, I do have a perminent 12v on the green wire and the red/blue wire seems to connect to ground. It is a PRHT car.
I found the 15A ROOM fuse, it is OK. Pins C and E are marked in the Haynes manual and they both are recieving 12v. It looks like the keyless control module isn’t operating the relay. Anything else I can check?
Problem fixed!! Actually it wasn’t a problem at all, just user error. Thank you so much for your time Richard. It was your comment about PRHT that made me check the roof. It turns out it wasn’t fully closed. I believe the boot solenoid gets disabled by the hard top controller if it isn’t fully open or closed, as you don’t want your boot lid hitting the hardtop while it is in motion.
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Ah good, you found it. Simplest results are always the best ones!
I was in the process of writing a clear explanation!
So I’ll post it anyway for anyone else who has the problem
ROOM fuse is under the bonnet in the fuse box next to the bonnet stay. It is a 15A fuse and if you look inside the fuse box lid it has a map of all the fuses.
The top of the fuse has the ends of the contacts visible so simply putting the +probe of your meter on both of them (-probe on ground) should show 12V if the fuse is intact. I’m guessing it is OK if other things in the car are working.
In my photo above the lower relay is for the lock solenoid, but its position could have been swapped with the other relay. I don’t know what the second relay does, but as a wild guess it might be for the rear fog light.
The lock solenoid in my photo has a black wire to ground and a blue wire from the relay pin D.
Wires in the above picture on my 3.75 PRHT car’s Lock Relay socket are then;
. Violet on pin A (relay coil).
Needs 0V to operate it, VIA either Dash Push Button and/or “Keyless Control Module” (remote control receiver behind the left end of the dash where the rain leaks in from the scuttle grommets).
. White/Red on pin E (relay coil).
Comes from the ROOM fuse VIA a switch in the PRHT module. Should be permanent +12V.
HOWEVER, if the PRHT module thinks the roof is neither fully up nor fully down this switch will be open to prevent you opening the boot, and then it will be indeterminate unless 0V applied to pin A.
. Blue/Red on pin C (relay normally-open contact)
Comes from the ROOM fuse. Should be permanent +12V
. Blue on pin D (relay common contact)
Goes to the solenoid.
With the -probe of your meter connected to ground, measure the voltage on the relay base by pushing the +probe in to touch the insert from the loom side. Don’t risk damaging the socket contacts in the base by stretching them with a probe.
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