You can get to the yellow wire by removing the radio. Before you do anything I would verify where the switch is going, because if it is going to the yellow wire it could be the problem. If it is attached to the yellow wire then there is no need to cut the wire again...just verify the connection. If the car is starting sometimes and not others then it sounds like something is loose. Your're going to have to get someone around you to take a look at this to see what you got going on.
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