You need a 12v 3ohm coil. These were standard on all the Volvo models between the demise of the armoured cable and the end of the 140/160 series. These will be plug and play. I can't say if 240 and later ones are suitable but if you've tried one of these and it gets very warm it's probably 1.5ohm. You need a 3ohm one which will measure 3 - 3.2ohm or so. Coils are usually reliable enough to get one from a parts car. The Volvo ones are Bosch black and similar ones are on VW aircooled. Bosch blue are fine too and are considered "sports" versions, but I doubt if you'll notice any difference. Take a meter to the pick 'n pull and meter across the 2 small terminals.