Took my '91 (92MY) for a quick spin last night only to find the check engine light on, speedo again not working along with the trip computer, the wiper washers. reversing lights and most prob a few more things....
Do the all share a cable plug or earth (ground) somewhere ?

 

I don't have the 91 electrical guide, so can not comment on the commonality of grounding in your harness.

The speedo and TC could be related. Other than that I would treat each fault separately to begin with. Start one problem and find the cause, fix it and move on. DO NOT shotgun the problems or you potentially will never fix them.

Work methodically and start at one end of the electrical guide and work through each connector and ground point.

 

They are all in the drivers foot-well if that helps.

 

When you say the trip[ computer is not working, do mean there is no display or that the speed/mileage is not workling?

If you get a display, try turning the key to on (do not start the engine) and see what codes show up.

 

Thanks guys for the help. Had another look at it today as I put her in the "naughty corner" for a couple of weeks....lol.
The all had a metal relay under the dash in common =. Bosch 0332014113. Same relay as the fuel pump. swopped out and all worked. So now to get another relay.
Agu 1068 is the new replacement.