I removed all the dust. I'll get some of this for the corrosion. Thank you!

 

Let me start by saying I'm no motorhead - far from it. I just bought a 2003 F150. The battery was dead when I test drove it so I guess that should have been a red flag. They put in a brand new battery for me but after sitting for a couple days, it was dead. Figured I left something on but then it happened again so I started to troubleshoot by scouring forums. As many have suggested, parasitic battery drain can be caused by many different things (after market components, glove box lights/switch issues, bad batteries, GEM modules, bad ground, etc...). As suggested by many, I started by having the battery and alternator tested at local auto parts store. After all, it's free and easy to do. My battery tested fine (it was new so no surprise) but the voltage regulator on the alternator failed the test. I bought myself a new alternator and installed that morning. I thought great, this could have been a lot worse based on others experience. I tested the charge and it was at 12.8 volts. Just to be sure, I tested again a few hours later and to my surprise the battery still seemed to be draining fast. My multimeter did not have a current/amp function so I had to buy a new one in order to test draw ($36). I went through the process of pulling fuses one at a time while keeping an eye on the current. It was at about 2.5 amps until I pulled the fuse for the Powertrain Control Module. Now I was thinking that I had a bad PCM but then I realized that there was a relay for the PCM. In order to test, I swapped the relay with the fuel pump relay and the issue definitely followed the relay (I could hear the fuel pump continually running so I pulled it out right away) Bingo! After all my troubleshooting and a new alternator, a simple $10 relay was the source of the issue for me. I'm sharing my experience because I didn't see anyone else mention this as a possibility. I wish I would have done the amp/draw test prior to swapping my alternator. Maybe it wasn't such a bad thing if the VR was bad but makes me wonder about the validity of the test/tester at the auto store. Hopefully this helps someone else.

 

This seems as if it could be my problem because my battery only drains if I leave the battery connected, it's worth a try. Is there any other way I can test the relays? (Don't own a multimeter)

 

I can't think of a good way to track down this type of problem without a multimeter (one that measures DC Amps, not all of them do). However, they aren't very expensive (under $30 on Amazon - the one I bought was Sperry for $36 at local home store) and they are a great addition to your toolbox for any do-it-yourselfer. If you watch any videos (EricTheCarGuy was very helpful for me), they all start with eliminating the battery as the issue (test for free at any auto store) and then going to the multimeter to test various components by pulling fuses. I suppose you could just replace the relays one by one and see if the problem persists, but you may end up ruining your battery in the mean time. As I said previously, there are many causes of battery drain. Relays are but one of them.