Technical Reversing light switch types and conundrum

[fiat500]

I know it won't be a common problem here as the reversing light switch really belongs to the late-model 126. But there are some clever and/or experienced people here and someone might have some useful experience of this, (which I have posted elsewhere).

The switch I obtained for my gearbox is the correct thread and dimensions and is activated by the reverse selector-rod inside the gearbox. In neutral and any other gear than reverse, the plunger of the switch is normally depressed which closes the internal contacts and would provide a circuit to ground or to return a live feed.

When reverse is selected the selector-rod inside the gearbox moves away from the plunger of the switch and the contacts are open. This is the opposite (reverse ) of what I expected as I have wired a circuit so that this switch would activate a relay and supply a feed to the reversing light when reverse was selected. I presume I now need to obtain a switch that works the opposite way to this.

So I'm asking what is the terminology for a switch which when in its active position is normally open.....maybe I answered my own question?

Or is there a way I can make this setup work with the existing switch?

 

[giardini]

So I'm asking what is the terminology for a switch which when in its active position is normally open....

It's called a "normally closed" (NC) switch. The circuit is closed in the rest position.
As opposed to a more usual NO switch.

 

[fiat500]

It's called a "normally closed" (NC) switch. The circuit is closed in the rest position.
As opposed to a more usual NO switch.

I'm on the way to finding one now.[emoji3]

 

[fiat500]

For my own and for anyone else's future reference, I've ordered one for a Mitsubishi Pajero/Shogun; Lucas SMB769 Replaces ME581047. It has an M18 x 1.5mm thread and is normally closed. It might not have a sufficiently long plunger but I can get around that. It also has a fitted cable-tail and plug which looks to be a more resilient setup than the bare spade terminals usually fitted; the plug itself may have to be replaced with something more generic.

I still don't understand how the supposedly correct switch doesn't work the right way round.

I'll report back the outcome.

 

[Bigvtwin996]

For my own and for anyone else's future reference, I've ordered one for a Mitsubishi Pajero/Shogun; Lucas SMB769 Replaces ME581047................................

Well having experienced Shogun Reversing light switch....
I hope that it's replacement is much easier that on a Shogun, as it is located in top of the gearbox (possibly so it does not get soaked in oil!!) you need to be as dextrous as Eugene Tooms (lets see who can identify him without Google) to fit it.
The one I had had cabled attached, they are rather thin in comparison to most auto cable and rather inflexible... so keep an eye on potential oil soaking or cable breaks...

 

[fiat500]

I hope that it's replacement is much easier that on a Shogun,

.... it's a doddle to get at on the Fiat. I might just hold fire on the Shogun part though. Late news in is that the switch for the 0.7 Cinquecento and 126 BIS might be correct in every detail, (it would be wouldn't it?) :bang: I think the gearbox end-cover I'm using might be a really late one, possibly off a BIS which have a a long plunger. Earlier switches (which is what I randomly have) are shorter. I've got it to work by making an extension piece between the switch and the end of the reverse selector-rod. The Cinquecento part has a very long plunger which might just do the job.

 

[Bigvtwin996]

.... it's a doddle to get at on the Fiat. ....................................

Now you are really getting into this "modding Scene"
Are you ready to try....
VW Cylinders and 246 Dino Rods?

 

[fiat500]

Now you are really getting into this "modding Scene"
Are you ready to try....
VW Cylinders and 246 Dino Rods?

...:....no...then I would have to really start releasing the moths...I've got a phobia....spending money.

 

[Bigvtwin996]

...:....no...then I would have to really start releasing the moths...I've got a phobia....spending money.

I once saw a complete set of Ferves Ranger running gear for sale...
that would have made a superb conversion kit for a 500 to 4x4.. ideally suited to the Highlands....

 

[giardini]

Peter, I'm curious to see if you get what you're hoping for with your order, or if there's a semantic trap in the terminology I offered.
As I understand it, your original switch gave an open circuit when free-standing, but a closed one when mounted and inactivated (plunger depressed).
So does that make it NC or NO ?
If the "installed" state is the reference, and you ordered NC, then you'll get the exact same thing you had before, won't you ?
If so, I'm ready with the lame excuse: "But I was only trying to help".

 

[fiat500]

"But I was only trying to help".

...and you did. You obviously understood what was getting at, even if I didn't understand myself.:bang:

I can't even get clarity from some eBay sellers about this, so I resorted to self-help, assuming that a wiring symbol on the box, which indicates a closed switch will mean that the component will be in that state when the plunger is in its unactivated, undepressed position, which is what I want.

If the switch I have previously been provided with is correct in dimensions and operation it follows that the reverse-switch location and mechanism must be different on the earliest 126 models, because the plunger is too small and is open at its inactive position.

It may be delivered today so i'll report back.

 

[giardini]

Further "help".

What about an NC relay switch with your original gearbox reverse switch then ?
One that cuts the feed to your light when activated by the depressed plunger, and establishes the feed circuit when the plunger extends...
If such a relay exists... (it must).

Just trying to make sense of your weird gearbox switch Ahhhh

 

[fiat500]

Further "help".

What about an NC relay switch with your original gearbox reverse switch then ?
One that cuts the feed to your light when activated by the depressed plunger, and establishes the feed circuit when the plunger extends...
If such a relay exists... (it must).

Just trying to make sense of your weird gearbox switch Ahhhh

I considered changing the relay for one with an extra terminal which would be normally closed, but that would have meant that for all of the time, except when in reverse, the relay would have been powered in the active mode.

The switch arrived and is a fine specimen which fitted perfectly and does the job perfectly. I don't know what car the gearbox extension I fitted is taken from, but the switch intended for the Fiat Cinquecento 700, (a car which apparently was never sold in the UK), is the right one.

 

[ubot]

The switch intended for the Cinquecento 700 is compatible with 126 Bis.