what is the wattage of my headlights can handle, without blowing a harness.

 

Everything I've read here indicates that ANY wattage above what the stock bulbs draw will cause wiring harness problems. There have been a number of posts on a harness upgrade, but I can't tell you much about it. The search function should get you plenty of hits on the subject.

 

Go with an upgraded harness. The are plently of posts in the archives that will tell you how to make one yourself, where to buy a pre-assembled one, and where to get them.