Let me know how it goes. Also, the early volvos have a notorious problems with relays. Poor solder joints. I would also pull the fuel pump relay, behind the ashtray, I believe its the furthest to the rear and left. You have to pull the cig lighter and coin tray out. Pop the case, and exaim with a magnifying glass, you can resolder. Your year group is also a victum of engine wiring harness deteoriating. But don't look for a new one, around $400. You can get a used one for under $200. I have an 85 740, original owner. I'm posting another link that has a wealth of info for 700/900 volvos.
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