2002 Ford F150, Battery Goes Dead Overnight

This 2002 Ford F150 came in with the complaint that the battery would go dead overnight. After the basics of checking the battery and alternator, I disconnected the negative battery cable and installed my Fluke multimeter in series between the negative battery post and the negative battery cable. I set the meter to read DC amps and adjusted the test leads accordingly. As you cane see in the next picture there was a sizable 2 amp draw on the system.

I turned my meter so that I could see it while working at the underhood fuse box on the driver’s side of the engine compartment. When I lifted the fuse box cover the drain went away. Since there is no switch that monitors the position of the fuse box cover, my educated guess was that a stuck relay just became unstuck. Not a good feeling because I do not know at this point if I could get it to stick again. Just for kick I closed the cover again and to my surprise the drain came back.

After opening and removing the cover, a simple visual inspection found the problem. The covers on the two larger square relays were not sitting level in the fuse box. I pushed down on the top of the two relays and found that the one on the left of the next picture to be the culprit. Pushing down on the cover made the drain occur and removing pressure from the cover made the drain disappear.

With the relay and cover fully removed for inspection, I thought I saw the problem.

However I was positive about it when I looked at the other damaged relay. Note the difference in the positions of the metal tabs at the top left corner of each relay. The tab on the left relay is bent out to a nearly horizontal position compared to the one on the right.

Two new relays installed and the 2 amp drain was gone. In case you are interested the upper relay in the next picture is the PCM relay and the lower relay is the fuel pump relay.

I find it unlikely that many of you will run into the same situation but I thought it might be interesting anyhow. The ironic thing about this vehicle is that there was a real .1 amp drain on the system after the relays wee replaced. My thought is that someone attempted to find this .1 amp drain and in the process caused the damage to the relays. The .1 amp drain was caused by a faulty add on electric brake controller. I located it by removing one fuse at a time in the fuse box above. Note the row of three pink, 30 amp PAL fuses. Removing the center fuse in that row made the .1 amp fuse disappear.

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