It would be easier to just replace the fuse holder with a new one that has a sealing cap in the same location (what I did).

Your wet weather problems are a rotted wiring harness. If you're going to pay someone to replace it; get ready to spend at least $700.00usd. The harness cost is around $350.00usd. You can do it yourself or repair the old harness and save a bunch. The insulation falls off the individual wires inside the loom (the outer covering) when two wires in fairly close proximity have lost their insulation; water condenses inside the loom and makes partial contact between those wires and can give false readings to the ignition ECU that will cause rough idling, stalling, poor performance, etc. When it dries out the computer (sometimes) won't reset untill you re-start the car.

When I was going thru this I noticed that if I warmed the car up during wet weather for 20 minutes it still ran like crap sometimes, however: When I shut it off and re-started everything was AOK.....sound familiar?

I'm driving a 1986 240DL with 900k miles.

You can go to a local parts store and check out the trailer accessory/electrical area. They have waterproof fuse holders for around $5.00 that you can wire in. I had the same problem with mine and it is less than a 30 min job to solder and heat shrink the new fuse holder into the wiring harness.

Also check the wiring where it runs down fender. It is subject to abrasion wear and after time will short out, most often when it is raining.

ipdusa.com sells a waterproof replacement fuse holder for this location.

You should take a look at the other connectors around this area as well. Around the coil, under the power steering reservoir, etc. Clean them all up with sandpaper and put them back together with dialectric grease.

I have always had a problem with this fuse. I fixed it when I had to get a new wiring harness. The wires got brittle with age. I agree it is in a poor location, just make sure it is covered. There are too many 240's out there which have the plastic cover missing and then when it gets wet the fuel pump just stops.
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95 850, 88 245

Can't tell ya why they put it there, but it's the main fuse for the fuel injection system, powers the relay for the fuel pump.
It's a 25A blade type, the only one used on the car by the way, and the fuseholder is available at your local dealer for about $3. That ought to cure that problem- it's a common failure.

A lot of folks have replaced it with a waterproof fuseholder from an autoparts store. Make certain to disconnect the battery cables when servicing- that one wire can deliver a lot of current.
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Rob Bareiss, New London CT ::: '87 244DL/M47- 229K, 88 744GLE- 218K, 82 245T-181K Also responsible for the care and feeding of: 88 745GLE, 231K, 87 244DL, 239K, 88 245DL, 246K