'89 Volvo 240 DL doesn't start in the rain

My Volvo 240 DL has had trouble starting in the rain for about four years. It has recently gotten much worse (usually I can start it after a while). It always stalls at traffic lights, but once I get it going for maybe 10 minutes, it drives fine. I just took it into the shop because the alternator lost all of it's charge. They put jumper cables on it for a long time to give it a charge, but it still wouldn't start (it had been pouring rain all day). They then replaced the distributor cap and the spark plugs, but it still wouldn't start. They told me it might be the fuel pump, but they don't know and aren't sure about working on it anymore. Does anyone have a suggestion of what it could be?

 

It is a good idea to replace with OEM spark plug wires. Check the fuel filter and fuel pressure. Have a look at the timing belt..condition.