Electric
 

I have a 1981 380sl, the electric is a little screwy. The windows don't go down, the turning lamps dont go on, the brake lights don't go one, the brights don't go one, and the horn no longer works. I changed the fuses, still no luck. I used a test light, there was no power going to the fuse. Tested the relays, they have continuity. Could it be a ground? I'm stumped right now.

since they all (some ) are on different fuses , I would say common ground issue. Check 12 V on both sides of fuse box ,on all fuses

My suggestion would be: Check under the center console. Former owners are not noted to being the best electricians around. Check your emergency flashers making sure that they are wired correctly.
Verify fuse power source for the windows, Verify power going to the switches under the console.
Check the power source or sources running from the + buss bar behind the radio. Check all grounding as panda says.

There should be +12V on each of the "supply" rails of the fuse box (down the center if I remember correctly). Take a voltmeter or test light, make sure you have one lead on a GOOD ground (bare chassis metal, tight body screw, no paint) and check with the other lead / probe. If you don't have 12V on one side, you need to find out where you are losing it. The older fuses are notorious for having a corrosion problem which 'opens' the circuit.

Because I've been an electronics tech for so long, I'm a strong advocate of purchasing and learning how to use a multimeter. They aren't necessarily that expensive, and can tell you a lot. There are online tutorials that will help you learn how to use them. But sometimes the $2.95 ElCheapo Industries (tm) test light can be just as useful.

Good luck

One of these days, I'm going to finish that Automotive Electrical Troubleshooting tutorial.

Scott