Hi David,
The circuit is in the 1997 wiring diagram page 60
The relay 2/53 pin 1B gets it's switching voltage from the ECU pin 38
It's a Blue -Pink wire You can check this wire for continuity.
Do this first.
You can check/service ECU power and signal grounds:
31/50 power ground
31/51 signal ground
and the engine power and signal grounds
31/32 engine power ground
31/33 engine signal ground
see 1996 manual page 51 (PDF page 127) for pictoral locations
The 97 manual indicates the circuit description for your engine management is:
(SFI) Sequential Fuel Injection, Motronic 4.4 (B5254S)
Look for your exact engine on the Volvo id sticker to confirm the exact engine you have.
I found a discussion of the SAS here:
https://volvo850wagon.wordpress.com/2013/03/08/73-secondary-air-system-fault-vacuum-leak-p0410/
There's some input to the ECU, some sensor to switch the SAS maybe the O2 sensors?
Somewhere there should be a circuit description for the air pump from Volvo.
Bill
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