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In an attempt to sort out the lit SRS light I have fitted new, good quality plugs and sockets to the under seat wiring and replaced the rotary coupling. The light is still on so the car is off to a local auto electrician who has a T4 reader. However I have been inspecting the coupling I took off the car. The yellow wire that connects to the air bag has a twin, female coupling that is plugged into the air bag. On the rotary coupling itself there are two sockets for plugs from the wiring loom. One of these is a multi connection which I think is for the horn. The other socket has two pins which I assume connect to the yellow wire. However these two pins are joined so in effect there is only a single wire going to the air bag. Does the return go through the steering wheel itself and if it does why the dual wires to the bag?

Jan T
 

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mg_tf
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The rotary coupler is a fairly simple device and in effect it’s a flat ribbon cable coiled up inside the coupling, it’s quite easy to test it with a multimeter. You say you’ve replace the plugs and sockets on the seats, are you sure the wires are connected the same way round as original? If you get one or both of these wrong the SRS light will stay lit. A T4 will pinpoint the issue, a Pscan is also good with these sort of issues and will tell you exactly what the issue is.

The result you get measuring the yellow cable that makes it look like it’s a single cable could be caused by the fact that some of these yellow SRS plugs/sockets have a short in them until the plug/socket is plugged in. I think I have a spare one I can measure later.

Bob
 

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mg_tf
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Regarding the apparent short between the 2 air bag wires, if you look very closely into the bottom of the socket for the air bag on the back of the rotary coupler, you’ll see both pins are shorted together by a metal link, this link is pushed out of the way when the plug is inserted, thereby removing the short. I suspect this is done to prevent any pickup or static triggering the air bag if the plug isn’t inserted. From memory the seatbelt pre-tensioners have a similar arrangement.
 

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There are several systems that run through the rotary coupler including the steppy switches or audio controls, the same coupler is used on most MGR models.
 
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