VDO Classic tacho Hay Wire

Hi Guys
Have had problems with my VDO Classic tacho since installed when completing the hot rod.When the car is first started the tacho works great but within a minute or so the reading starts to rise and after about 3 to 5 minutes the tacho is reading about 5000 rpm when it's only about 1800 rpm.
The distributor is a electronic Accel 7100 breakerless.I have tried the MSD TACHO convertor and a few others with no solution.( The tacho has been bench tested and is fine ) I have also wired in a cheap tacho to the car and it operates ok and the vdo classic works fine on my sons car with a standard distributor.Any help would be much appreciated.

It sounds like you have a poor ground -

I believe that your tach has a modular connector on the back with 8 pins. Make absolutely sure pin 3 is grounded. If need be, run a wire to the negative post on the battery to test. The only other pins that are used are:
Pin 2 - goes to switched 12 volts
Pin 4 - goes to your tach output put on the MSD box.

Hope this helps,
Glenn

Additionally, there are two different MSD adapters, the 8910 and the 8920 and for the VDO, you need the $60 version(8920) (http://store.summitracing.com/partde...5&autoview=sku) and then it still might be marginal from my limited experience with my VDO instruments.

Thanks Guys I'll look into both idea's.I have tried one of the MSD tacho convertors but I 'll look to see which one it was and I've tried an auto meter tacho convertor as well.
The ignition system does not have an MSD it only has the Electronic ACCELL distributor

Nick