Just to cover myself. You are playing with a system that controls an explosive device so if you do
this and none of the airbags go off in a crash or your newborn is catapulted out the rear window,
I'm not to be held responsible.
I did this on a 2007 fortwo, I can't guarantee it'll work on any other 451.
So far, 2 people have tried this using the official switch and it hasn't worked (air bag light
on permanently no matter what position the switch is in). However, 2 people have bodged it
in the same way I did and it worked fine. This doesn't mean that bodging it will work though.
My suggestion is you don't follow this guide and get it done properly at smart.
Take off the silver dash end trim on the passenger side. Underneath are a few Torx screws that hold
the cover on. Remove the screws and remove the cover, you should now see this. Look in through
the hole. If you have a left hand drive smart, just look up under the dash on the passenger side.
This is the connector you are looking for. Yellow housing with 2 wires. Brown and Green/Black.
Pull the connector out. Here's a closer look for you to compare.
Once it has been pulled out you have a choice, fit a switch or bodge it.
Look at the plastic just to the right of the connector shown below you can see the cut out in the original panelling where the standard smart airbag off switch goes.
...and it's very obvious looking at the fascia panel where the switch would go.
I'm not going to recommend you bother buying a switch from smart. It's just a standard on/off
switch that you need and the smart one uses a key barrel that can only be turned with a key.
That sounds a hole load more expensive than a cheapo round toggle switch.
I found an airbag off switch from another car which could be used.
Fit the switch in the fascia, you'll probably have to Dremel the hole out to the size you require.
Cut the yellow plug off and solder them to the switch contacts or crimp on some female spade connectors and push them onto the switch terminals.
With the connector pulled out of the hole you can refit the fascia trim and the cover trim which leaves the yellow connector nestled nicely between the trim and the door rubber seal.
Get yourself a paperclip, unfold it and jam it in the only 2 holes that have connections in them.
With either of the above done, flick the switch or apply your paperclip and start the car.
The airbag light should go out and immediately come back on. This tells you that the passenger
airbag is now deactivated. Turn the car off, flick the switch or remove the paperclip and start the
car again. The airbag light will go out and stay out which indicates that the airbags are functioning.
If you spec the airbag off system, you get a light in the front roof trim that illuminates
when the passenger airbag is deactivated. On cars without the airbag off switch, there
is just black plastic blank in that position. I did try adding an LED as seen here.
However, even when wired up to the correct connection which was behind the roof trim...
...it didn't function as it should have done. It just illuminated no matter if the airbag was on or off.
I'll put that experiment down as a fail but not having the light doesn't affect the on/off modification.
Just for the sake of showing you, here is the position of the airbag controller.
and here is a nice close up shot so you can see the label and connections.