Electrical problem in our van

Hi, I posted this query on misc.consumers.frugal-living since I know the folks there. I was directed to repost this here and hopefully get some ideas on
how to fix this problem.
Original post:
We have an electrical problem in our van. We are not sure if we should take it to a dealership to see if they can figure out the problem because our mechanic is stumped. So I thought I would present the problem here to help us decide what's the most frugal thing to do with it.
Our van is a 1996 Plymouth Grand Voyager, 79K miles. Since last Monday, it's had an intermittent starting problem. When you turn the key, everything works but the engine will not start. Our mechanic discovered that a fuse was blown in the part of the transmission that tells the car it's in park. Replace the fuse and the van starts fine until the next time it blows that fuse. We can't tell if the fuse is blown until we try to start the van (that is there is nothing unusual happening while we are operating the van). Our mechanic is racking his brains but hasn't be able to figure out what is blowing the fuse over and over.
Two weeks ago, my DH installed a new CD radio in the van. He's a very meticulous guy and followed the directions carefully. The odd thing was that the battery was dead the next day. It was an old battery - original to the van. It was so dead it could not hold a charge and we had to buy a new one. The van then worked perfectly for a week until this electrical problem popped up.
When the van didn't start last Monday, we had it towed to our mechanic. He replaced the fuse, checked all the systems and couldn't get the problem to reappear. We got the van back the next day. I drove it to Aldis, then to Tops (another grocery store). At Tops I couldn't start it and had to have it towed again to the mechanic.
Our mechanic doesn't think the new CD/Radio could've caused this problem but he took it out, checked all the wiring, drove it all around with the radio out and later put the radio back in. He couldn't get the fuse to blow again. So on Friday when I went to pick up the van, our mechanic said that he thought he solved the problem but just in case, he wanted me to take a spare fuse and showed me how to replace it. Good thing he gave me that spare fuse since the damn van decided not to start in the parking lot of the local copy store. I popped in a new fuse like I was shown and off we drove back to the shop. After I got back and turned it off, it couldn't restart. During our drive back, it had blown the fuse again.
I'm not sure who hates this van more, me or the mechanic. My suggestion that I drive around with a case of fuses was not met with much enthusiasm.
We are wondering if we should take the somewhere else. What are people's experience with electrical problems? Is the fact that he's not finding a solution a sign he's not competent or are electrical malfunctions always so complicated?
Chris
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Chris Jung wrote:

Could be just a coincidence, but I certainly would suspect the radio that was added. Try taking it out for a week or so of driving and see if the fuse still blows. If it does, then I suspect that you are somehow pulling power through the circuit with that fuse when you use the radio. Hard to say without seeing how it was wired.
I wouldn't call the mechanic incompetent just yet as electrical problems can be hard to diagnose, especially when they involve equipped added to the vehicle later.
Matt
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have your tech remove the left front wheel then the inner splash shield then carefully inspect the wiring harness that runs from the battery/pdc to the inner body by way of wheel well
Chris Jung wrote:

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