I found that the wires to the sender connector had been poorly
repaired, and both had corroded through, breaking connection. But
after repairing the connector, the speedometer still doesn't work. SO
now I need to get to the connections at the back of the instrument
cluster and check continuity through the sender circuit. I don't know
anything about what a good sender is supposed to read...if it reads
open, I will put a jumper in the sender connector and then I should
read continuity if external wiring is good.  Do you know of anyway to
test the sender...perhaps it is supposed to read so many ohms static?
No doubt in operation  it is generating some type of pulses, maybe a
scope is required.  If the wiring to the sender checks out good all
the way to speedo, then probably it is the speedo itself, I guess.
A rebuilt one for my Mercedes was about $150....would it be about the
same for Volvo?