Hi I have just finished building a MK1 Twin Cam and have fitted an Accuspark ignition system has any member any idea if it is possible to get the original tacho to work

I am putting together a twin cam instrument cluster for a Mk1 with a 2L pinto. The last time I played with this tacho with its original electronics, it didn't give a very accurate reading. It seemed to be effected by the dwell (which it shouldn't be). It worked intermittently and then I discovered that the circuit board was cracked.
 
On a side note, I gave up on the whole thing and decided to design a new twin cam instrument cluster from scratch. So I designed a printed circuit board that controls everything. I am keeping all the gauge faces and replacing the 2 mechanical gauges (oil pressure and speedo) with analogue versions (that use remote sender units) as well as replacing the coils for the temperature, fuel and voltage and controlling them with a microprocessor. This is obviously a far more complicated solution!

ive got a twin cam with an accuspark and my electrician got mine to work

Hi PlotJ - seems you are a bit of an electronic whiz- I'm looking to replace my tired old tacho and mechanical speedo with electronic versions, particularly the speedo. Mine is an MK2 RS.  Any suggestions for a late model conversion- a wheel sensor driven speedo in particular?
Cheers,
Len

Hi Len,
The short answer is, it's complicated.

Let's look at the tacho first: The tacho is simply an analogue meter with some electronics driving it that reads the signal from the ignition points. I am not sure if the electronics requires a fixed dwell (angle that the points remain closed) from the distributor. If it does, and you have new electronic ignition (e.g. Powerspark) then the tacho reading will be in error. This is because modern electronic ignitions limit the time that they effectively "close the points" for when the engine is at lower RPM. You can test this with a portable dwell/tacho meter hooked up to your car. Typically, tachos simply need to be calibrated to read accurately. There are probably some adjustments available but I don't have a Mk 2 unit so I couldn't tell you. Again, you can check the accuracy with a portable tacho meter.

As for speedos, this is a bigger problem. I used a tacho (yes that's right) gauge out of a some Mitsubishi instrument cluster that I found on someone's hard rubbish collection. A printed circuit board that I'm working on will drive this with some analogue electronics and a microcontroller like modern cars. I have constructed a speedo sender unit that attaches to the gearbox and sends a signal to the electronics which then drives the analogue meter (from the Mitsubishi). There is the added problem that you need an odometer as well.
So, this is a complicated solution. I'll post some photos when I get it going.

Cheers,
Peter.