As many of you know, the original ceramic fuses used in our car are a bit troublesome. The small contact areas mean that they are extremely sensitive to corrosion, and although the fuses are covered by a clear shield, they are still very exposed to the elements. I had enough of turning my fuses in the sockets and scrubbing at the contacts every other month. This, in addition to restoring the connections throughout the wiring harness, will greatly improve the electrical system in your car. You will notice brighter lights, more stable gauges, and for those of us running EFI, a more stable voltage in the system.
Notes: This guide uses a fuse box from a 1976 USA car. Your fuse box may be slightly different, but the same process still applies. Be sure to disconnect and remove the battery before doing any electrical work in order to eliminate the possibility of component damage or personal injury.
The first step is to remove the fuse box from the car. It is held in place with one sheet metal screw, and simply lifts out. Be careful to not damage any of the wires as you pull the fuse box from the cutout in the fender. You will likely only be able to pull the harness out a few inches; take note of where the connectors attach (they can be attached more than one way, but only one way will work), and be sure not to miss any of the individual connectors. If the connectors are difficult, you may pry on them GENTLY using a flat head screwdriver. Make sure they come off evenly so that they do not bind.
With the box out and on your workbench, take a picture to note which way the color coded insert goes.
Remove the card. Be careful; it is very delicate and tears easily. While it is out it is not a bad idea to laminate the card in order to insulate it and protect it. I don't know of anyone making replicas, but one of us should. In addition, it would be a good idea to determine which years and models had which cards; there is some variation.
Remove the fuses, and take a picture of the contacts before doing the work so you can see just how big the difference is later.
Begin by giving the fuse box a good cleaning with some mild soap and water, just to get out any dirt or grime that is present. Don't bother trying to clean the contacts now; you'll be wasting your time.
Sneak yourself a bowl from the kitchen, and steal the vinegar out of the pantry. Any kind of vinegar will do, but a white vinegar (I used apple cider vinegar) will be a wise choice. While you are in there, grab the baking soda and salt as well.
Begin by placing the fuse box in the bowl, sprinkling some salt on it, and pouring in the vinegar.
Stir it up, and shake the fusebox around in the mixture for a few minutes. The acidity of the vinegar and the abrasiveness of the salt will quickly work together to remove the oxidation from the surface.
Let it sit for a while in the salt-vinegar mixture while you prepare a baking soda neutralization bath for later on. Mix about a table spoon of baking soda and a cup of water. The concentration of the solution is not crucial.
Once the neutralization bath is made, we can go back to the fuse box. After sitting for this long, much of the oxidation has already been removed. We can do better though. Grab a chunk of steel wool, and start scrubbing.
Halfway through, the improvement is obvious.
With the scrubbing done, it is time to rinse the fuse box multiple times in water (deionized is preferred, although tap water will do just fine), rinsed in the baking soda bath, and then given one final rinse using water to remove the baking soda. Thoroughly dry the part using compressed air (or set out to dry if you don't have compressed air available).
Now it is almost time for re-assembly. Grab your di-electric grease. If you really don't have any available, vaseline will do, but you are really better off using the grease as it is far more durable.
Get your fuses. ONLY USE OEM GERMAN FUSES. Mercedes has fuses available for a fair rate; I grabbed a bag on ebay for cheap. They are the proper, high-quality ceramic units. Not only will they operate far better than anything else, they will outlast other fuses and look correct in the fuse box. Now take your nice, new fuses and throw them in the acid (vinegar) to remove any oxidation that has collected on them while in storage. You WILL notice a difference. Remember to neutralize them afterwards!
This looks better.
Tighten down the prongs so that they hold the fuses VERY snug, but do NOT deform the tangs. Bend the curved section of the tang, do NOT bend the whole tang as you will weaken the base. Make sure they all look about even, and coat either end with grease. Insert the correct fuses into the correct slots, being absolutely certain that the bases are sitting properly in the holes at the bottom. When the fuses are all installed, smear some more grease across the bridge in the fuse in order to coat the exposed copper section.
Reinstall the card on the back, and cover the nice, clean connectors with more di-electric grease.
Go back to your car and using a flat head screwdriver (as shown) deform each connector in the socket SLIGHTLY. Too much will damage the connector and prevent the male prong from entering easily. Only do enough to give the connector a fresh surface to bite onto.
Re-install everything and pop on a new cover while you are at it and enjoy your improved electrical system. For that finishing touch, find some compressible water-proof foam to replace the seal between the fuse box and the shell that has completely rotted away. This will greatly improve the life of the fuses and the performance of the electrical system. Short of converting to blade fuses, this is the best thing you can do.
PRO-TIP: If you can soak the connectors in the vinegar bath (and then neutralize using the baking soda solution), even without scrubbing, you will improve the connection. This is a good way to quickly clean many connections in the car.