The other day I was doing some electrical troubleshooting, and thought I would check the fuse box. Confronted with various size fuses, I compared the fuses that were in the box with the ones listed in the owner's manual. Lo & behold, several had different amperages than they should have. I used a combination of some new fuses and old ones found in the trunk-lid tool tray, buttoned everything up, and turned on the ignition. Everything worked as it should, EXCEPT the power to the radio was coming on and going off at intervals (every 1-second).
It turned out the culprit was an old fuse (not blown) which had been in the tool-tray for several years and had gotten corroded inside the plastic casing. The cure: out with the old, and in with the new. Check your fuses not only for correct amperages, but do a visual inspection for any corrosion inside the translucent plastic fuse casing that might keep the fuse from working properly.
Notes from Chris Behier: For cars with Fuses under the hood, (BMW, Porsche, etc...) the combination of heat and humidity makes it hard for the insulation to keep corrosion at bay. Therefore, checking your fuses and using some light sandpaper (330 grit) to freshen up the fuse terminals is not a bad maintenance item to do. Depending on the level of humidity and heat of your area, you may have to check after the first year, and then at 6 months intervals if you decide to skip the cleaning part.
Author: Rick Sparks
Sonnenflecke, May/June 1999
Sunbelt Chapter BMW CCA