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I had a short circuit in my 89 740 in the #5 fuse circuit; it handles interior lighting, radio, power aerial, trunk and engine compartment lights, etc. It was there for a long time because the previous owner could not find it. He lived without those luxuries. I bought the car two weeks ago with the short included in the price. So I pulled apart trim panels, pulled out lights, pulled the door panel off one side and after about ten hours of looking around basically decided that I could not find it. I got a post back from a gent who suggested that I build a short circuit detector; so I checked eBay and found one for $15 plus shipping.
I found the short in ten minutes!! The gadget really works well. You plug one side into the blown fuse negative side and the other into the positive battery terminal; you must remove the positive cable from the battery. When you plug this thing in it fires up with an internal light and buzzer so you know you're on the right circuit. You pull the little mangetic dial indicator from its pod and run it along suspected harness areas. If you're on the right harness, when the console pulses - every ten seconds - the indicator needle jumps in the direction of the short. As you get closer to the short the needle jumps further. If you pass the short the needle stops jumping because all the current is going through the short into ground. The short was a pinched wire under the rear rocker panel trim where the trunk harness runs up along the rear wheel well. I would have never found it without this tool. Great gadget. It really works well and saved me many hours of work.
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