$$$, oh yes definitely if you're planning on an almost complete restoration, it seems. I know you don't have the cars yet, but I'd definitely try and rule out the wiring itself as the cause of your electrical gremlins. I couldn't even imagine trying to rewire a w124, or any other benz for that matter. That s**t runs everywhere!! I'm definitely on your side as far as putting the money into it, though, if you're not planning on selling it. My receipts, including the purchase price, total nearly $40,000, including a $12,000 trip to the body shop to fix some collision damage, some rust, and do a full color sanded and polished re-paint. If I was planning on selling the car at some point, I'd be out of my mind to put that kind of money into it. But I'm not, so it's just for me
. It has never left me anywhere, not once, in 9 years, so I'm not going to leave it! Oh and btw, after a coolant flush, as everyone here will tell you, only use genuine MB coolant or zerex G-05
Moral of the story is, the easiest way to find problems is to start driving it. My car was only used as a "station car" before I got it, and never went more than 3 miles round trip daily. I started driving it 40 miles round trip on the highway every day, and in very short order the problems showed up, got fixed, and never came back. These cars love their exercise! Enjoy!