Have a 1999 Ford Explorer Xlt. I purchased used about 2 months ago. When I got it, I did not drive it often, but started it daily. I keep it in a carport so that it is not in the rain. There was no antenna on it just the case where one should be. I purchased a Scosche universal antenna and use the universal thread adapter to put it in. It is plastic and covers all metal pieces. I used the original parts that were still on the vehicle. I just added the antenna and 1 thread adapter. I did this about 3 weeks after owning the car. After a few days my car battery was dead. I have charged the battery and had an electrical test done to find out what would cause it to die. The radio fuse spiked really high amperage on the meter so we removed the fuse. It ran and stayed charged for 2 days the 3rd day it was completely dead again. A month later I removed the antenna that I put on and the tread was completely corroded. The battery light in the car is not on and shows it is right in the center where it belongs. The fuse in #1 slot says it is for a power antenna, but I do not know if the one that was missing was power or not. This all seemed to start after I put in the antenna. I do not know what caused the corrosion in the antenna or the battery drain. Could they be related? Where else can I look?
Remove the negative cable. Hook the voltmeter in between the negative cable and the battery. Put it on milliamp scale. The reading should be below 50 mA. If my remove the hood light bulb then remove the interior fuse that controls the door lights. Start removing the fuses and have someone watch the meter. When it drops below 50 mA that's the fuse your draw is on.