J Sweet: question on speedo sender

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?

 

It's a reluctance pickup, so all it is is a coil on an iron core, so it
will have some resistance but I'm not sure how much. If you get an open
circuit from it then it is bad, I'm not sure what could have caused that
though.

No idea how much a new one costs but given the exceptional reliability
of them, I'd look at a junkyard, any 700 series and probably any '86+
240 will have one that will work.

 

OK...great. Now that I at least know it is a coil I know how to
appproach troubleshooting it. Yea, it will probably turn out to be
something other than the sender. Geronimo