Hello,
I have a XJ6 Coupe, 4,2 1977 with a series 3 XK engine fitted with twin Su Carbs.
I was about to install an Accuspark Electronic distributor a few days ago and pre-checked the wiring and coil beforehand. I was disturbed to find that the coil was connected to the distributor from the Positive side. The book tells you 60% efficiency loss wiring up the wrong way. Accuspark point out you will blow their kit with this arrangement. I have a ballast resistor. Then I noticed that was wired up to the negative terminal on the coil and strangely connected to a single brown wire on its opposite end. Please see my labelled diagrams for clarity. Before and Now.

The car has been working many years with this arrangement. However, starting up from hot was becoming a real issue. I worked through timing and carbs and made a few improvements but couldn't solve the issue. By now the car was 'running on' after shut down and I decided to go for an Accuspark set up.

I have now rewired the car without installing the Accuspark conversion. I decided I had too many unknowns to deal with before doing that. I have switched the connections around so the distributor now connects from the Negative. What I assume to be the live feed from the solenoid starter is fed to the ballast on one side to connect with what I assume to be the start wire from the ignition on the opposite end of the ballast. The ballast and these brown wires now connect to the positive coil side.

The car is running without start up issues and no longer runs on. A big improvement. However, the tachometer (rev counter) no longer works. I read in the book that it is wired in circuit with the CB negative side of the coil and relies on a pulse from the distributor. Swapping wiring has stopped the Tachometer from working.
I have several questions.
How do I know which brown wire is which.... Start wire from ignition and feed from Solenoid? I don't know which is which.
Have I got it right with the wiring I have now? Hopefully someone can check their car and compare.
How do I get my tachometer working again? I suspect I have the wiring wrong seeing as the Tach has stopped. The car is however improved to the point were I think I won't bother with the Accuspark just yet.
Any help with this would be fantastic.

Many Thanks.

PerErs.