Just wondering if I can use my spare 3W ignition for a 3W 150 with my DA 150??? or do I need one from DA

Why would you want to do that!!?? Get one that will work and stay with the DA unit.

If it is the old style 3W you should be able to use it, I let a buddy use my spare 3W ignition when his DA ignition went out and ended using a DA ignition on my 3W 150 when I plugged the battery in backwards and fried my 3W ignition. If the 3W ignition is the new style (the one with the tach lead) it will not work.

If you utilize the pick-up as well as the module and its earlier vintage its doable. The DA and 3W pick-up units are wired differently, that said one could rewire the pick-up connector if need be. The inverse is true too, a DA ignition system will work on a 3W. The latest 3W ignitions are not compatible for swap overs as the hubs require a different magnet orientation if memory serves me.