940 93 speedo not working, circuit board corrosion

[olov]

so I'm trying to get my $200 93 940 turbo running, speedo doesn't work, the wire was ripped out of the sensor on the diff, but I tried the "shorting the wires at a pace of 4-5 shorts per second" from https://www.volvoclub.org.uk/faq/ElectricalSpeedometerRepair.htm and nothing, I traced the wire back to the dash and tried and still nothing.

so then I pulled the cluster, and the back of the speedo looks different from the one pictured. and then one corner of the back of the speedo has what looks like corrosion. this is the corner of mine https://imgur.com/ijqBAiS with the corrosion and the picture on volvoclub.org https://www.volvoclub.org.uk/faq/ImagesSpeedometerRepair/Speedo5A.jpg

there's not a ton of clusters on ebay(and I'm not paying $200 for one), junkyards around here don't have them. I'm thinking this is the problem and I'm going to solder wires and bypass the circuit board - sound ok? anyone done that before? or am I barking up the wrong tree and the problem is somewhere else?

tried to solder but at 450F I couldn't get solder to stick. just going to buy a cluster off ebay when I find a cheap one

 

[84B23F]

speedo doesn't work

1994-940 shows a ground is required, and its found to left of of your left foot...pull off panel there...maybe BN-GR wire...clean them grounds.

1993-940 shows differential sensor feeds speedo and ABS using same wire color coding. Might see if cruise works, when a differential sensor is replaced.
GRN-WHT
BRN-WHT

I sometimes use a Tach for Speedo, when my speedo is not working. A smartphone app can give a GPS based speed.