Hi Glen,
Like Spook says, the bulb sensor relays are all the same, basically all the later 900/700/240s in the late 80s and beyond use the same sensor (the 3rd brake light becoming standard caused the changeover).

As far as your bulb indicator going out after touching the brakes, there's really only three likeloods.
1) If it's a KAE relay then absolutely swap in one of your others. I've had nothing but problems with two KAEs in my two '95 940s, and lord knows I've done enough swapping around, cleaning sockets and changing bulbs to convince myself they're oversensitive to something about my lighting systems.
2) Given your symptoms then more than likely, actually extremely likely, the relay currently installed is suffering from micro fractured solder joints. This so common it's almost laughable. Re-flowing the main (brake light) solder joints on the two tiered PCB boards inside the relay would almost certainly fix it. In yoir case with a box full of spares, just swap it out and put a felt penned ? Question on mark on the old and throw it back in the box.
3) Cleanup the brake light bulb sockets, including the 3rd brake light) and make sure the bulbs are the same brand and equally aged. This won't be your problem, but clean them up anyway niw that your working this area. If this was the only source of your problem then it would be different. The indicator would only be coming on when you touched the brakes.

I'm jealous of your box of spares. I'm using a bridged bad sensor in the car that needed the KAE, so no longer have the bulb sensor feature in that 940. Next time I trip over a cheap used Volvo one I'll grab it and restore functionality.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now