Tachometer Conversion Pt2
After that it’s fairly simple. I cut down and used the aftermarket plastic mount to hold the RVC module itself, with 2 small bolts as shown to fix it into the Lotus casing. I spaced these to fit the two holes already in the steel casing used to mount the OEM RVI module and also retained the OEM rubber gasket.
The photo shows the 3 screws that mount the RVC module in the plastic shell. I suspect the two small gold screws are for adjustment, but as this seems at least as accurate as the current tachometer when I tested it, I haven’t touched them.
Now to wiring it up
New unit ready for mounting in OEM casing
The OEM circuit incorporates an induction loop with the wiring going from the ignition switch to the +ve side of the ignition coil. Obviously when you remove the OEM tach you’ve got to join the two wires from this feed together to make the ignition circuit.
Wiring for the new unit
The new circuit is equally simple although you have to run a lead from the tachometer through the car and into the engine bay. You need an earth, an ignition switched +12v supply and an ignition system detector which in this case a green wire connected to the -ve side of the ignition coil.
On this tachometer there is a fourth wire for the internal illumination, white in the previous photograph and shown as purple in the schematic, which is connected into the panel light circuit if required.
And this is the finished conversion.
I must confess that the photograph is better than the real thing because you can still see the shadows of where the original dial mounting screw holes were if you get the lighting just so, but in this shot the flash has hidden them.
The same photograph angle appears to show the dial off-centre but it’s not. Having the two mounting bolts in oversize holes allows you to center it up quite reasonably.
And once mounted in the Europa binnacle the shadow marks will be much harder to spot, and I certainly won’t see them !
The converted tachometer ready to go
Originality fetishists will note that the screw spacings are different, plus the screws themselves are larger and more obtrusive than the original Smiths ones. I must confess that’s not going to worry me too much, I’m more interested in the instrument working for the next project, which is “Electronic Ignition”