As i am modifying my 940 turbo ... i am removing the dash, but i need to know whether i can just hook up an aftermarket tach straight tot he tach input on the volvo dash. i tried this in my 740 and it didnt work so i am dubious about trying it this time.

Also i want a new fuel guage and odometer (speedo). I am sure i can find the wire feeds for these using my haynes, but a little more info is needed for the compatability issues that might arise.

There is no problem with all the warnign and indication lights as i have a T shape rally style cluster with blinkers and all the usual handbrake (ahem which is mostly on) main beam oil warnign etc...

Matt

replying to my own thread hmmm ...

I understand from reading various articles in my research that the ignition amplifier controls the negative switching on the coil to initiate a spark to the plug.

because this is negative switching i am not sure wether the aftermarket tacho's use negative or positive switching. I have a bog standard aftermarket one, quite cheap and is registers nothign at idle and only begisn to register at like 100-200rpm when the engine is at around 3k!! I have it set to four cylinders also.

The only thing i can deduct myself, with my reasonably limited knowledge of electronics and components is that this tacho may use positive switching so therefore needing an OP-AMP piece of circuitry to reverse the negative polarity of the car to positive for the guage ... This seems to me like hassles ...

Can anyone elaborate on that for me?

note: research was in various other forums, some turbo-bricks etc... My haynes manual guide to engine management and places in my haynes 940 manual aswell some 740 bits and a multimeter. I will see if i can get an oscillator from someone to really test.

Matt