I've seen a few posts on here (admittedly mostly old) stating that import vehicle seats have a different electrical connector on the underside compared to the UK spec ones. Moreover, the import seats have an extra wire.
e.g.
l viewtopic.php?f=9&t=50557 (http://www.mr2roc.org/phpBB3/viewtopic.php?f=9&t=50557) l
l viewtopic.php?f=11&t=46910 (http://www.mr2roc.org/phpBB3/viewtopic.php?f=11&t=46910) l
l viewtopic.php?f=8&t=32538 (http://www.mr2roc.org/phpBB3/viewtopic.php?f=8&t=32538) l
I haven't seen anyone saying for certain why the difference exists though (if such a post exists, please point me to it). I think I know why the difference exists but I'm having difficulty googling something more authoritative than just what I have worked out from my own experience.
From driving a few imports, Japanese Domestic Market vehicles often seem to have a sort of seat belt tension reducer device to make the belts feel more comfortable. It makes the belt feel slightly looser across the chest.
From m http://www.takata.com/en/products/seatbelt02.html (http://www.takata.com/en/products/seatbelt02.html) m
Quote from: "takata.com"The tension reducer is a device that lessens the feeling of restraint and confinement when the seat belt is fastened. It helps reduce the force applied to the winding of the webbing around its spool.
I first noticed it with my Mazda M X 5 import (more accurately, a Eunos Roadster). When I got the car, the seat belts felt normal. However, I noticed a wire had been disconnected to prevent an annoying buzzer sounding if you started the car with your seat belt off (lots of Mk1 M X 5 owners do this). Reconnecting the wire made the buzzer work but it also made the seatbelt feel a bit different; a bit looser, perhaps a bit more comfortable? Other than that, the seatbelt worked like it was meant to.
Spin forwards a few years to my MR-S. When I got it, I noticed the same kind of feel to the seatbelts as I had in my Eunos and in a few imports that friends had owned which I had driven since my Eunos. After a while, I decided to change the cloth seats in my MR-S with leather ones from a donor UK spec MR2. As other people have described, I noticed that the connector on the JDM seat was different to the UK seat and that the JDM seat had an extra wire. Based on my experience with the other cars, I had a hunch what the extra wire was for. I also had both the male and female connectors from my donor car so I grafted the UK spec connector on to the loom of my JDM car, leaving the original one in place, so that I can now plug in either a JDM or a UK seat.
Anyway, long story short, after fitting the UK seat, the important stuff worked as it was supposed to: the seatbelt operated normally and the dash light telling you to put on your seat belt worked as expected too. However, the seatbelt now felt more like a normal UK one. i.e. the slight tension relieving effect had gone.
So, I'm pretty sure that's what the difference is and that's what the extra wire is for. It's for a tension reducer device. Quite why these don't seem to be in UK spec cars, I don't know (or maybe they are and are just not connected). There seems to be precious little information about them that I can find but there will be thousands of cars out there with them and I'm guessing many owners haven't even noticed (the effect is quite subtle). It also seems that removing the connection to the tension reducer doesn't affect the safety of the belts in any way. Without the tension reducer connection, the belts work just as they should: a sharp tug on the belt and it locks, otherwise it pulls out and retracts as you'd expect. I'm aware of cars with tension reducers connected and disconnected going through MOTs numerous times without issue.
Following as I feel my seatbelt is uncomfortably tight across my shoulder. It would be interesting if you are correct and if something could be retro-fitted to the UK spec cars
Just to add to this. At the time I wrote the above post, I had only ever fitted UK spec seats into a Japanese spec car. Because the JDM spec has the extra wires, the plug in the car is bigger and so requires a bigger socket on the underside of the seat. Therefore, a little rewiring is required to put UK seats into a JDM car - either to put a smaller plug on the JDM loom or a larger plug on the UK seat (or bypass the issue entirely with your own connections I guess).
I have now looked at what happens when you put a JDM seat into a UK spec car. It's much easier. The UK plug just goes right into the JDM socket and the seatbelt warning lamp (etc) works just fine. The JDM plug/socket is basically the same as the UK on but with an extra set of pins. The UK plug in the car goes into the JDM socket on the seat, attaching to the two pins at the top (nearest the retaining clip - which the UK plug also fits into) and the two lower pins remain unconnected. I shoved a bit of rigid foam in the unoccupied space inside the JDM socket just to ensure that the UK plug didn't wiggle around but it seemed pretty secure anyway.
Rough diagram of seat socket...
(https://i.imgur.com/lwC8skq.jpg)
Don't know if this is related but I've got two seat belt assemblies here. Both for passenger side.
I need to have a closer look because it seems that there are two different parts: 2002-2004 and 2004 onwards
73220-17151-C0BLACK, TRIM1*, 2*, 3*, 4* (08/2002 - 01/2004)1€ 200.38
73220-17220-C0BLACK, TRIM1*, 2*, 3*, 4* (02/2004 - 08/2005)1€ 200.38
The boxed one I have is the latter, the unboxed is the former. I'll have to inspect them for differences as well.
Would be ever better if I had a jdm one to compare