6 replies to this topic

[r1mcnally]

Greetings from Tennessee, USA.  I own a 1989 Rover Mini 1000 (RHD, air conditioning, automatic transmission) that appears to have, at some point before I bought it, had a Lucas tachometer added to the drivers' glove box door.  Two years ago when I started working on dash ducting I thought I took photos of which wires went where before I unplugged things, but alas, it appears I did not.

 

The back of the tach has three male spade connections: one marked +12, one marked 6, and a third with no apparent marking.  Wires running to the tach's mounting location are a green wire, a purple/white wire, and a white/black wire.  For clarification, when I say purple/white I mean a purple wire with a white tracer.

 

At the coil a green wire and a white wire are connected to the positive terminal, and the negative terminal has two white/black wires.  The white/black wire at the tach's mounting location does have continuity with both white/black wires at the coil.  The purple/white wire is a mystery.

 

With this info, my question is two-fold.  First, any idea where which wires should go where at the back of the tach?  And second, is there a way I can test the tach to make sure I didn't damage it when I hooking it up the way I thought it originally went?  While the tach did work correctly before I unplugged everything, when I connect it now it doesn't work.

 

Many thanks for any help.  I haven't been able to find anything about this Lucas tach, though there's plenty of info out there about Smiths tachs.  Apologies if I attached files incorrectly, my Photobucket account is ancient and it seems I have to upgrade (pay) to share newly added photos.  -R

Attached Files

•  tach0.jpg   43.59K   2 downloads
•  tach1.jpg   39.84K   6 downloads
•  tach2.jpg   65.84K   7 downloads
•  tach3.jpg   52.43K   7 downloads
•  tach4-wires.jpg   21.88K   2 downloads

[gazza82]

+12 could be the 12v feed

but I can't see a terminal on the +6 position ... might therefore be a 6v circuit


It's weird one though ..



Green/White would normally be an ignition activated circuit.

Purple/White would be permanent live

White/Black is possibly the coil pulse/feed as White is the ignition circuitry

[KTS]

looks like it may be a Lucas branded VDO unit 

 

according to the link below +12 terminal should be 12v in (possibly the green wire :  does that have 12v with the ignition on?), the 1 or I terminal would be the signal wire (White/Black from coil), and the last terminal would be for an earth.

 

http://www.914world....hp?t230715.html

 

 

purple with a white trace is the colour used for the interior light circuit.  i would expect that wire to be in that location, but would normally connect to the passenger door light switch.  if you earth that wire do the interior lights come on ?

[r1mcnally]

looks like it may be a Lucas branded VDO unit 

 

according to the link below +12 terminal should be 12v in (possibly the green wire :  does that have 12v with the ignition on?), the 1 or I terminal would be the signal wire (White/Black from coil), and the last terminal would be for an earth.

 

http://www.914world....hp?t230715.html

 

 

purple with a white trace is the colour used for the interior light circuit.  i would expect that wire to be in that location, but would normally connect to the passenger door light switch.  if you earth that wire do the interior lights come on ?

 

Thank you for the replies, everyone.  Gazza82 is right, there is no spade connection terminal at the "6" position. 

 

The green wire does get 12 volts when the ignition is turned on.  So, I connected the green wire to the tach's +12 terminal, the white/black wire to the tach's 1 terminal, and to the 3rd tach terminal I connected a jumper directly to the negative battery terminal.  I started the engine and no luck, the tach did not move.  I checked all connections to make sure they were well connected and no change, the tach was unresponsive.

 

As for interior lights, the only one I know of in the car is the little ceiling light above the B pillar on the passenger side.  It's never worked, even with a new bulb.  Maybe because that purple/white was never connected correctly?  Regardless, I dropped the light assembly from the ceiling and did not have continuity between the purple/white wire at the ceiling light assembly and the purple/white wire behind the dash.  I also didn't find any voltage on any wire at the light assembly, so I must have a break in the wire(s) or a blown fuse.

 

What signal should I expect to see on the white/black wire at the tach connection when the engine is running?  And, is there any way to test the tach to see if its still good or been damaged?  

[KTS]

with the engine running you should get a 12v spike on the black/white wire with each spark - with a DC voltmeter connected I would expect to see a slight reading that increases with RPM

 

Apologies; saw your location and assumed it was a left hand drive car !  the usual routing for the purple/white wire is from the interior light down the passenger A pillar to the passenger door light switch and then daisy chained across the back of the dash to the drivers door light switch

 

power to the interior light was usually from an inline fuse in the engine bay - i'm more familiar with the wiring on the older cars so yours may be a bit different in places

[cal844]

If there's no pwer on the Purple/Orange wire at the interior light then check the inline fuse on the same wire colour in the engine bay

[r1mcnally]

Thank you for the info about what to look for on the white/black wire, KTS.  With my voltmeter I did see voltage that increased with engine speed (good).  However, the tach didn't move (bad), so it seems that I indeed zapped it somehow.  I think I saw a place online that said they fixed tachs; I'll have to look them up.  Oh well, at least I can say mystery solved.  Many thanks to everyone for all their help.  

 

Now I can work on the unconnected purple/white wire I found back near the tach mounting area, as it would be nice to have interior lights.  I'll look for a fuse issue under the bonnet - thanks, cal844.  A handful of wires under the bonnet seem to change color as I trace them out - my '76 from NZ had no such wire shenanigans going on, so it looks like there were "repairs" done by a previous owner.  Wish me luck!  -R