Hello, a few years ago, the speedometer in my ‘88.5 coupé started intermittently failing, for a few seconds at first, but eventually the needle fell and would come back maybe 1% of the time.

We have installed a new transducer in the diff., and tried multiple instrument clusters compatible with my year, all of which behave exactly the same: the speedometer needle doesn’t move, the mileage doesn’t change, and the trip computer doesn’t get updated mpg data.

Any thought about what we can try next?

Thanks in advance,
Rhett

 

Hi Rhett

On the assumption that you have cleaned all the Contacts on the back of the Instrument Binnacle, then it could be a bad Earth, where it has become fairly Normal to add an Auxiliary Earth wire to the back of the Binnacle and so that is the first thing I would try

But since none of those other 'Gizmos' appear to be working (Trip Computer etc) then it is even more highly likely that it could be the 'Black Box'

So where is the 'Black Box' ?

If you follow the wire from the Transducer in the Diff, all the way into the Boot/Trunk you should then be able to see where the wire disappears over the top of the inner Wheel Arch/Fender and down a gap just big enough to get your hand in and although you won't be able to see it without the Aid of a Mirror

Somewhere down inside that slot is the little Black Box and that could be the thing that needs replacing

 

Mistaken post.