740 speedo sensor

AAARGH! I was advised at the MOT that my speedo sensor wire was is danger of being cut by the handbrake cables and so taped it up - whereupon the speedo stopped working. It turns out the original wiring to this was replaced at some stage. Although I have remade the connections the speedo doesn't work. I asssume it is a Hall effect sensor - if so, does it matter which way round the wires go? can't see why but I am willing to be corrected. Anyone know which fuse - if any - serves the speedo - nothing listed in the handbook. If so could the speedo itself have 'blown?' though a short? All contributions welcome. Thanks John D

Hi, well as you have had no replies here are my findings. All the instruments use the same positive rail for power (clock aside) so if your fuel gauge works then the fuse is ok for the rest. As far as the sensor is concerned I would rewire to the correct config, my records show you should have a brown and white and a green and white within that loom, these both go to the abs control unit (if fitted). The manual is vague on which fuse serves the dash instuments, it could be one of 5 - again its model dependant. Good luck Regards AF

My suggestion is that if the speedo worked immediately before you taped the wire up, that you have disturbed (or created) a bad connection. Check the plug at the diff (use switch cleaner as well). If that section of cable has already been replaced, check how well/badly it was joined.

All sorted. I gave up trying to check/repair the wires that had been spliced in at some stage with various cable connectors and just ran new wire straight from the boot to new connectors. Worsk perfectly now. I still find it irritating that there is so little advice given on testing and fixing instruments in workshop manuals these days. Or am I just getting old and grey......! Thanks to all who offered suggestions.