Tachometer Wiring

[richardy8496]

I removed the dashboard of my early +2 to get it reveneered and I'm now trying to put it all back together again. I marked up all the wires and have refitted most of them but one of the wires connecting the tachometer pulled out from somewhere and I can't work out where it should go. Attached is a photo as it currently is - the mystery wire emerges from the rather strange plastic square on the back of the tacho. Does anyone know where it should connect? Car is positive earth.

[Baggy2]

Hi
The loose wire connects to the ignition coil. As your car is positive earth I would expect it to go to the negative side of the coil. Assuming the car was running before the dash change the corresponding wire must be there somewhere . I think it should be a red wire with a green tracer in it.
HTH

[HCA]

Your loose wire is result of a badly connected bullet connector imo. Look around for a wire with a female bullet socket and a male connector inside.

[ncm]

Hi,
This is the back of the dash in my early 68 Plus 2 . The wire you have should fit into the connector highlighted in yellow, the wire disappearing into the loom highlighted in white. My car has been converted to -ve earth, hence the tacho sense loop being the other way round.

Cheers, Brian.

[Rob1n]

Hi Steve
I would advise replacing any 5 amp connectors you have in your wiring. That was one of the reasons that I rewired my +2. They can cause major problems and especially a fire.

[Billmack]

It's a white wire you are hunting. I'm going by my elan S2 and every other british car I've wired with that type of tach. The direction it is threaded thru that nylon block is important so I usually put a couple of connectors in there so its easy to reverse direction. It is in fact the same white wire that powers up the coil.

[ncm]

It's a white wire you are hunting. I'm going by my elan S2 and every other british car I've wired with that type of tach.

I don't know the wiring in a S2 Elan but the tacho wire on the Plus two is red with a green trace as shown in the pictures and the wiring diag. in the workshop manual.

Brian.

[billwill]

There are plenty of topics on this forum about Tacho wiring.


It has an Earth and 12v power line switched by the ignition switch.

Plus the power to the coil goes through a simple transformer which on early tacho is simply two turns wound onto a squared metal ring, but on later tachos the transformer loop is inside and is brought out to a male and female bullet connector. The white wire to the coil is cut near the tacho and fitted with a male and a female bullet connector. This enables you to connect the transformer loop by separating the two parts of the white wire & plugging them into the bullet connectors on the back of the tacho.

There are also some wires for the indicator bulbs and the night-time illumination, but these are pretty obvious.

See this search for more information on the Tachometers:
https://lotuselan.net/cgi-bin/search/se ... Tachometer

[richardy8496]

Thanks for all the suggestions but I don't think I'm any further forward. The reference to white wires refers to negative earth cars (I think) according to the wiring diagrams I have. The wires in question are red with a green stripe. The end of this wire that is not loose goes into the wiring loom and I assume ends up at the coil as there is a red/green wire attached to it. Once the wire loops round the bit of plastic on the back of the tacho, what is it supposed to be connected to? My wiring diagram seems to suggest the anti theft switch but I don't have one of those. There are no bullet connectors that are missing a wire. There are some nasty domestic connectors that have obviously been bodged in the past but there doesn't appear to be any sign of a missing wire.

[HCA]

Maybe it is not a bullet connector as we know them, it could be some other connection method - maybe even the two wires were just twitched together (oh yes, I have seen these!). The wire in your photo shouts 'bodge'.

If all you have done is remove gauges and switches and not messed with anything else, then somewhere behind your dash amongst the jungle of wires is a loose wire looking for its connection mate! It has to be there! Do not get too hung up on the wire colour as there are many reasons the colour might have changed.

I cannot remember with the early RVI tachos if it is possible to unscrew the loop block - I presume yes as you would not have been able to remove the tacho.

[billwill]

British Auto Wires Colours:
https://www.autoelectricsupplies.co.uk/ ... rder_2.pdf


Green with a red stripe is supposed to be a Fuel tank type wire, so has no proper relevance to a tachometer, so a previous owner had bodged up a wiring loom using any old wires he has around. You'll get nowhere talking about wire colours.

You will just have to read all those other topics I pointed to above and really understand what the tachometer wires do & then bodge it your way.

Or buy a whole new loom and rewire the whole car.

The thing you call a plastic square is probably supposed to be a piece of iron shaped in a U which fits onto a similar piece just inside the back to form the 'core' of a transformer. Plastic won't work. It has to be magnetic, i.e iron.

[mbell]

I don't believe Red/green is not the correct color for ignition power/tacho for either positive or negative earth cars. It should be white.

From your photo it looks like the wire goes to a screw block connector. That is certainly a modification by a previous owner. So you need to understand what changes had been made, so you need to start tracing the connections to figure it out.

There not much we can do here as we can't only guess at the changes made which is likely just to confuse you. If you can trace the connections and draw them in a diagram then we might be able to figure out what is going on. I would focus on where is the ignition power coming (should connect back to run contact on ignition switch) from and how should it get to the coil, via tacho

From there you should be able to figure out correct connections to make.

[richardy8496]

OK, thanks, guys. If the diagram you have kindly drawn is the same for positive earth, all I need to do is connect the loose wire to the live feed from the ignition. The comment about the square block having to be metal is mystifying - the block is clearly made for the job as it is a very precise moulding that fits perfectly in the carrier - the tacho was working before I dismantled the dash (albeit about 40% fast!) with that plastic (maybe nylon) block. Also I am sure the wiring colours are right - see the wiring diagram for the early +2 attached - clearly RG for the wire in question.

[HCA]

Why do all simple problems here end up in masterclass theory of inner workings of the item!
Concentrate on finding the llost wire is all that is needed here! mbell makes a good point re the screw block connecter. Look for one maybe that has other wires in it and check these are switched live, as a po might have teed in somewhere.
Be careful abandonning it and starting again - there ‘could’, note could, be a lost wire that is bare, resting on an earth….,remember, it is an unfused cct.
btw, yes the loop block is plastic.