When scowering ebay for new clocks to replace my miss matched items I came across a set from a MK10 which looked in decent condition, pending a repaint of the bezel. My knowedge was lacking somewhat and I assumed the tacho would be a standard type that counted the pulses from the coil.
Oh, but that would be way too easy. Instead Jaguar decided to fit a generator to one of the camshafts and use the tacho as kind of a volt meter, the faster the engine ran, the greater the output from the generator and the higher the tacho read. Later the R&D department would decide that a gearbox driven speedo was way to simple and propose a new device which unravelled a piece of knotted string with a lead weight on the end, coupled with a sundial and an abacus….
The speedo and revcounter…
So did I have to junk the new and much prettier revcounter? No, thanks to Spiyda electronics
They have developed a clever solution to convert the tacho to read coil pulses. There are two basic types, one that goes inside the tacho and one thats remote in its own plastic housing. I went for the remote system and followed the single page instruction…
Firstly srip the Tacho and identify the control circuit board. junk it
This leaves just the two wires going to the tacho movement
I just twisted link wires to the Tacho and the Spiyda module
and connected it back to the module as instructed.
add a positive and ground the attach the supplied signal cable to the computer headphones socket, one wire to ground one to the module signal feed.
This last bit is used for calibration and uses an audio file at a given frequency to set the tacho needle via a small screw that can be seen top right of the module.
I elected the 100Hz file which needed balancing to 2000 RPM on the tacho (this from a table of frequencies vs RPM depending on number of cylinders)
This dry run was to prove everything worked. next step is to properly wire and solder the leads.
I soldered new leads directly onto the Tacho coil. Note – there are no other wires now, just the new leads straight to the tacho drive. I put a blob of silicone on the dial to hold the wires away from the movement and left it to set overnight.
I’d made a school boy error and snipped the old electronics from the board. The board is used to mount the drive at the rear via 2 screws and the bit i’d snipped off filled the hole where the old terminals were.
I used some duct tape (on both sides) to seal the hole and made a small hole for the leads such that they were tight to pull through.
next to calibrate the unit with the help of Spiyda’s downloadable sound file.
Then put it all back together again and put the unit back in the dash.
This conversion really is ridiculously easy, the instructions are as clear as day and theres some help videos on YouTube too.
Once re-installed it works like a dream.
Spiyda will do all this for you for a very reasonable £95, but its an easy DIY job.
Right, whats next?