SRS

I have already looked and the wiring for the passenger side air bag is there .

Roverlike encapsulates my findings; with the correct devices it’s plug & play.
This was discussed at length a while ago & there were some dismissive comments which I ignore, going ahead irrespective.
I suspect you would be able to equip your car with judiciously bought items for little more than forty notes.
There was one ‘1600 ECU listed on eBay plus some brand new passenger ‘bags for coppers over twenty quid; a box of drivers ‘bags for a hundred & fifty.
These were being sold singly a couple of weeks ago also for around twenty notes.
Notanumber was looking to some brake master cylinders as a bulk buy, the drivers airbag would be worth considering but don’t count me in, I bought one earlier.
M

sworkscooper wrote:

I have already looked and the wiring for the passenger side air bag is there .

Do you have passanger side seatbelt pretensioner wiring in place?

If anyone is considering these changes I would recommend changing the under seat connector for a better example. A trip to a scrapyard to hunt for an improvement would be a good idea, I think my replacement came off a Rover 25.I think I’ve a picture on my phone, I’ll attempt to attach it. M

Yes . It's all there.

My last 115 didn't have a passenger airbag but had seat belt pretensioners (Inc wiring) for both sides. Would this have been standard for a single airbag setup or did most only have a driver's side pretensioner ?

I am of the opinion that pretensioners were fitted universally across the range.
If an accident occurs the system triggers the explosive charge in the belt buckle anchor point & it draws the belt in, taking up any slack in the system. In doing so it reduces to a minimum any lost motion within the network. This keeps both passenger & driver held firmly in their seat awaiting the airbag to thump them in the face.
As Roverlike has told up the SRS system is a stand alone network & the belt tensioners are part of that system.
The under seat connector is not the best & others could be used as I have said. It was not unusual for me to scrabble about under the seats persuading current to flow through the bloody thing & for the SRS light to extinguish, having changed them there hasn’t been a single instance of failure.
M