Richard Hobbs

After levelling off the steering wheel as part of the track rod/drag link replacement a few weeks ago I reversed out of the garage, heard a sudden crunching noise from within the steering wheel as I turned it and the SRS airbag light came on!

I had crunched/snapped the “rotary coupler” (also known as a “clock spring”) which sits behind the steering wheel to allow the airbag, horn and cruise control to maintain connectivity with the wiring behind the dashboard as the steering wheel rotates.

I then sourced a used replacement (part number YRC100350) from Land Rover Spares for £37 including VAT and postage (seen above). Brand new ones cost over £200, so pulling one from an old vehicle seemed like a good idea in this instance.

Also, I suspect the following isn’t perfect, but upon investigation I think this part number is fine in the following vehicles:

• Discovery 1 (300Tdi and V8) from 1994-1998 (from VIN WA762769)
• Discovery 2 (Td5 and V8) from 1998-2004
• Range Rover Classic (Soft dash models) from 1994-1996
• Range Rover P38 (All models) from 1994-2002 (from VIN VA346794)

Please Post a comment if you spot a mistake in the above.

Anyway, I stuck the multi-meter on all the pins in the new coupler to check for continuity and I found what I thought to be a fault. Both airbag pins had continuity with both other airbag pins at the other end (both red plugs). Basically, the entire airbag circuit was shorted out.

It turns out this is normal (when it is not connected, at least)!

Inside the plug which connects inside the dashboard there are a pair of shorting “clips”. These are designed to prevent the airbag going off as the coupler is disconnected underneath the dashboard (I think!).

You can see them clearly inside the plug in the photo below.

As this particular rotary coupler was knackered, I smashed the plug apart with a hammer and extracted the shorting “clips” to check that they really were there for that purpose and seeing them outside the plug shows that they are indeed for this purpose!

So basically, as you plug it in, the plug pushes the shorting “clips” away from the pins to break the short circuit and turn it into two separate connections as it is shown on the vehicle’s wiring diagrams.

So, for those who need to know what the other plugs look like here are a few more pics.

Above you can see the horn/cruise control plug which connects behind the steering wheel in the dashboard.

Below is the other side of the same plug, showing which wires connect to which pins.

Below is the horn/cruise control plug which connects inside the steering wheel itself.

The above plug and the airbag plug connect directly to the plug shown below.

Above is the plug on the “outside” of the rotary coupler (already mentioned just above). This is the plug that rotates with the steering wheel and it cannot be unplugged.

Here we can see the red airbag plug which connects to the airbag itself.

This plug has a coil inside it, which I’m told is to filter out any high frequency noise thereby preventing unwanted discharge of the airbag (which is discharged simply by providing a voltage to it I believe).

Above you can see the plug from a different angle so you can see which wires line up with which pins on the plug itself.

“What’s actually inside the rotary coupler?”, I hear you ask…

A 14ft/4.26m (roughly) coil of ribbon cable which tightens and loosens as the coupler rotates back and forth.

The coupler will handle roughly 5 complete turns, but the steering wheel only does around 3 turns from lock to lock, so there is plenty of slack built into it (as long as it’s centred properly before it’s fitted).

Above you can see the steering wheel side of the coupler. This is the part that rotates with the steering wheel.

Here you can see the dashboard side of the coupler. This is the part that remains stationary and does not rotate with the steering wheel.

Above you can see the entire coupler opened up with all 14ft of ribbon cable spread out.

And finally the part number and barcode, the part number being YRC100350.

One last thing to mention is that I was of the understanding that on a Discovery 1 the SRS light does not reset itself automatically, unlike the Discovery 2 and other more modern vehicles. This turns out not to be the case with my vehicle. I’m told that the Discovery 1 was of a time when they were still playing around with SRS (“Supplementary Restraint System”) and early Discovery 1 models had different SRS units to later Discovery 1 models.

Therefore, as I have one of the later Discovery 1 models, mine is capable of resetting the SRS light automatically once the connections are all back in place, but earlier models must have the diagnostics computer plugged in to clear the error code in order for the SRS light to go out.

It is likely that my SRS unit will keep the error in its logs, but it figures out that things are fine again all by itself and turns out the light. Earlier models also keep the errors in their logs, but do not reset the light automatically.

As of 1 Jan 2012 I believe this becomes an MOT advisory, and after 1 April 2012 it becomes an MOT failure (in the UK, of course), hence me deciding to fix it!

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