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TThere is no voltage supply to measure in the speed sender circuit. The sender generates a millivolt pulse as a magnet passes by the pickup head. Did you check for OBD codes as I previously suggested? You probably could have saved yourself a bit of time and effort getting at the sender connector if you had found no code present. A quick check underneath for damaged wiring at the sender is all I would have done.
Time to break down and remove the cluster.
There's a reasonable chance you can find and fix a faulty connection on your cluster without having to remove the speedometer unit. Ideally you will have a Volvo green electrical manual on hand to identify the associated connector pins to inspect and clean, also the connection from the flexible circuit board to the speedometer unit. I don't know of any '93 green wiring diagram manual that can be found online, but copies of the '94 (TP 3904202) and '95 (TP 3908202) manuals can be found with a bit of effort. They all use the same speedometer and will have the same cluster wiring. Note that the speedometer has it's own chassis ground wire that you should clean and remake. This is the brown/grey wire off pin 4 of the main connector -looks like it might be grounded to the side of the pedal mounting bracket. If the ground is okay then clean/remake sender circuit pins 3 (brown/white) & pin 5 (green/white) on the same connector. Next is to reseat the connector for the speedometer unit. After that you're following the circuitry from those pins on the main connector to the speedometer unit connector looking for damaged traces or a failed component. I see in the diagram a device on the trace between pin 3 to Sender+ speedometer connection which could be a failure point -it's not clear what kind of device it is, such as a diode, capacitor, small fuse or resistor -I'd want to check that out before deciding to replace the cluster. Carefully inspect the bottom edge of the flexible circuit board for a damaged trace. The bottom edge can get damaged during cluster installation at the wrong angle. A solder bridge across any broken trace is the fix.
If the problem is inside the speedometer unit then it's going to take a fair bit of skill and patience to remove it and get at the circuitry in order to do component testing. There are no circuitry diagrams for the speedometer unit. Procedures are in those articles I referenced for you. At that stage it's simplest to replace the entire cluster. You will not be able to change the odometer reading, so many people try to source one with similar mileage, especially if yours is a low mileage car. There is a security plastic tab on a back connector of the cluster that will reveal to future owners whether the cluster has ever been removed and possibly changed. Best to note original and replacement odometer readings in the owner manual or at least on the back of the cluster (I recall there's a place for that inside the cover of the owner maintenance manual).
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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