It is good practice to disconnect the wire from the positive terminal of the battery when doing electrical on a vehicle.
So the dash in your Mercedes is getting awful dim, what can you do!? Well there are a few different 'solutions' some of which are much better than others. The stock light bulbs are 3W (watts) each, some people like to put 5W bulbs in their place to brighten the dash. I do not recommend this route as it can create so much heat that things begin to melt. Remember you can solder with a 15W iron, so 2 5W bulbs put out a noticeable amount of heat. Well what should I do then?
First determine if you rheostat is working good enough or not. Now regardless of it you want to do it now or not eventually pulling the cluster (the set of gauges) is inevitable. While my rheostat isn't 100%, it seems to work fine so I went onto removing the cluster (you have to pull the cluster to change the rheostat BTW). If your cluster is loose you can simply jump from the one bar to the other, if there is a big difference you may want to either buy a new rheostat or solder a wire there permanently and just live with your dash always being set to high.
After removing the cluster from the vehicle I proceeded to clean each and every bulb off as in time they have accumulated some dirt which hazes the bulb. Just take some paper towel and put some isopropyl alcohol (rubbing alcohol) on it, the bulb must be free of ALL oils when you reinstall it so be sure not to touch it or let anything else pollute it. The lifespan of any automotive bulb is at least cut in half when the oil gets on the glass casing. I did this for all bulbs, and being that my backlight bulbs sometimes went out I decided to use a very minute amount of dielectric grease on the back of the brass tabs to stop this. Before you reinstall these bulbs you will want to clean the ‘prism’ so the light shines as bright as possible.
Basically the light bulb shines into a section of high gloss white plastic then at the very top some clear plastic routes the light around to the front of the dash where we notice the lack of light. By cleaning out or painting the prisms we enhance the light that the plastic can carry, hence increasing the amount of light on the dash. People have successfully used flat and high gloss white paints. I just cleaned the factory plastic by utilizing a Q-tip, dipped in isopropyl alcohol to help break it loose, then a dry Q-tip to wipe it clean. This seemed to work quite well on cleaning the prisms out. I also took care to clean the clear plastic piece which the light travels through. I did find a noticeable amount of dirt in the white prisms, so odds are it was on the clear plastic piece as well.
After cleaning these prisms, the clear plastic, and the bulbs (may be a good time to install new 3W bulbs) I took a little time and dabbed a little dielectric grease on all the pins that the harnesses plug into just to promote conductivity and make them disconnect easier. Afterwards I reinstalled the cleaned cluster into my car making sure that all the harnesses were plugged back in and the oil line was on snug enough to ensure it wouldn’t leak (it literally has oil in the line as it is a mechanical gauge).
The results I found were quite nice, I would say I had at least 3X more light after doing this as what I did before.
Removing the cluster, while it isn’t very complicated to do it does take some time and patience. On my 84 cluster there was one major harness, two smaller harnesses, a wire going to the tachometer, a ground wire, two dash lights, oil line (10mm nut), and a speedometer cable to disconnect. While there are hook tools which are designed to assist in removal of the cluster, they aren’t necessarily needed. One word of caution here, be careful to not pry the face of your cluster off, that is the way my 84’s cluster is due to a previous owner’s careless actions. The only tools you really useful here are a Phillips screwdriver (ground screw), 10mm wrench (oil line), and possibly either pliers or channel locks to help loosen a tight speedometer cable nut. You will want to have a shop rag handy when you break the oil line loose as it contains a small amount of motor oil in it. Back
Supplies:
Shop Towel
Paper Towel
Isopropyl Alcohol (aka, Rubbing Alcohol)
Q- Tips (or white paint)
Dielectric Grease
Tools:
Phillips Screwdriver
10mm Wrench
Channel Locks
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