1850HL 1975 factory fitted micro switch

[stevevx52]

Hi All - I acquired the above car last June, whose bodyshell is in amazing condition, thanks to plenteous wax oil, but with a very worn and tired engine and gearbox, let alone front and rear suspension bushing. I've spent this past winter rebuilding the front suspension, engine and gearbox. However, whilst removing the instrument panel to install a combined oil/water gauge I pulled on what I thought was a loom connector to find a small RS components micro switch came apart leaving three wires which were part of the main cable loom in tact. The switch itself being held in a very over engineered long square tube that was bonded to the underside of the dash. I can find no reference to this switch or wiring in either of the Factory/Haines manuals I have.
Does anyone know of this switch which I now believe to be some sort of ant-theft device to isolate the ignition?
I've just ordered a replacement switch from RS and would like to understand its intended purpose and where the three wires connected to it are linked to. White, I have found continuity to the ignition switch, Black I assume is earthing and Green have no idea!! What I do now know is that I cannot re-start my re-built engine until I either bypass this switch or replace it with new and correctly wire it.
Cheers
Steve

[Carledo]

I can tell you it isn't standard or original fitment for any Dolomite.

I would guess you are right and it's some kind of immobiliser, you'd have to trace the green wire to it's destination to work out HOW it works, but white is an unfused ignition live wire and black is earth, so the only wild card is the green (normally fused ignition live but may not be here)

I can imagine an "either or" switch where "either" is live through to ignition and "or" is earth, but earthing an unfused ignition live would be dangerous, at best it would run the battery flat quickly and at worst could start a fire.

If I owned it, i'd delete the circuit and return it to standard. If I lived in the sort of area that makes an immobiliser desirable, i'd engineer one so I KNOW how it works!

Hope this helps, Steve

[stevevx52]

Hi - many thanks for your input. However, having removed the instrument panel again today to trace the 3 wires from this micro toggle switch there is no doubt it was Factory installed and not either a Dealer added option or Aftermarket bolt on. I've taken some photos which I hope I can add to this message showing the wires in place as part of the instrument panel loom.
Referring to the wiring diagram for RH cars from the intro of 3mm pin harness, I now know that the light green wire is connected to the Tacho into a single spade connector which also carries 2 Dark green wires, one of which is fed power from Fuse 25.
The white wire is also connected to the Tacho onto a bullet terminal, which also carries a white and slate wire. The black wire definitely going to earth via one of the three instrument panel plugs.
It's a complete mystery to me and I feel sure there must be other Dolomites fitted with this switch but I can understand owners being oblivious to it as I was until I tried to remove the instrument panel, as the steel holder that house the micro switch cannot be easily seen or removed from its housing. I hope these photos may ring bells with someone!
Meanwhile I will be replacing the damaged switch with new and will see what happens!
Steve

[matt of the vivas]

Definitely not an original fitment, it's been put there by a previous owner. If it's connected to the tacho I'd imagine it simply shorts the ignition link to earth, cutting the ignition.
Matt.

[xvivalve]

Your white wire in the first picture has a crimped connection to the wire it is attached to; as others have said, definitely not OE.

[Carledo]

The white slate lead on the tacho is the pulse sensing lead from the coil, the 2 dark greens are fused ignition feed in and a further loop across to the voltmeter. Which is all as it should be.

So this very non stock abortion is creating a parallel circuit to earth the coil power as an immobiliser, which you can easily dispose of, since the original wiring is still doing what it's supposed to. Just cut back the light green and white wires as close as possible to the terminals on the tacho and the black one wherever convenient. Job done!

I presume the car is still running on points? If you put an electronic ignition on it, i'm sure this thing would blow it up in very short order. All my other thoughts on the dangers of shorting an ignition live to earth still stand as well.

Steve

[stevevx52]

Thanks Steve - for your thoughts. The car as purchased last June does run on electronic ignition with no issues.

I completely understand the comments made by you all about this matter, but I am adamant that the wiring loom on the rear of the Instrument panel is original Factory quality and untouched by any dealer/owner, until I made the mistake of pulling on the switch which fell apart, so I could remove the panel. Only at that point did I extend the white wire to re-solder to the switch as it was slightly shorter than the other two and was making the re-connection difficult.

The workmanship of the metal holder for the switch and how it was bonded to the rear of the dashboard frame is no lash up by a DIY'er. I have significant experience of working on many makes of classic cars over the past 50 years and as a retired engineer from the diesel engine and aerospace industries I do know a thing or two!

I have a replacement switch arriving today from RS so this saga will continue!
Steve

[soe8m]

Thanks Steve - for your thoughts. The car as purchased last June does run on electronic ignition with no issues.

I completely understand the comments made by you all about this matter, but I am adamant that the wiring loom on the rear of the Instrument panel is original Factory quality and untouched by any dealer/owner, until I made the mistake of pulling on the switch which fell apart, so I could remove the panel. Only at that point did I extend the white wire to re-solder to the switch as it was slightly shorter than the other two and was making the re-connection difficult.

The workmanship of the metal holder for the switch and how it was bonded to the rear of the dashboard frame is no lash up by a DIY'er. I have significant experience of working on many makes of classic cars over the past 50 years and as a retired engineer from the diesel engine and aerospace industries I do know a thing or two!

I have a replacement switch arriving today from RS so this saga will continue!
Steve

Well as said, it's not original and a home made DIY.

Jeroen