Speedometer troubleshooting... Please help!

[grant964cab]

Hi there,

I'm hoping someone could give me some good advice on troubleshooting a speedometer (and odometer) on a 1991 964 cabriolet.

I have cosmetically rebuilt a car that was abandoned 25 years, a LHD American import that is extremely low mileage. New interior, dash, paint and roof... I've not fiddled with the electrics nor major mechanics, though I suspect some of the forward electrics have been tinkered with at some point.

I've read loads of forum posts to try to work out why I have no speedo or odometer.

The wiring contacts: relays, fuses and connectors etc have been checked for corrosion (none anywhere).
I've checked the speed sensor Left front, it works seems to work correctly at roughly 1000 ohms and changes as the wheel spins.

I've replaced the large blue relay R52.

The Antilock idiot light illuminates on ignition on then goes out on startup.

And that's where I am...stuck.
Other info: the spoiler switch never worked, I figured as I've read that the signal goes "speed sensor>Abs>Speedo>spoiler" that this will not have any impact?

My questions are...

1/ Is there a way to test a relay? (sorry if this is a noobie question!) I can't just go around buying relay after relay to check them! Can you just work them out and then bridge the pins? Or use a voltmeter and power source to test their functioning?
2/ Is there a way of using a voltmeter at the plug for the back of the speedo? - that way I can say the fault is the speedometer itself if the signals arrive here correctly. <----- obviously this is the best test as it eliminates half the system!
3/ I saw a post of someone saying swapping the relays R33 and R34 worked for them. Why would this work, the connections look different!
4/ Is there anyway to reset the car without a Hammer?

Any suggestions or guidance warmly received, I'm in the Newcastle, UK area if that makes any difference!

Cheers
Grant