I have a '97 F150. It is a V6, automatic. I've had it since I bought it new and this problem just started out of the blue a few months ago.
If I let it sit and don't drive it for a few days, the battery goes dead. I haven't installed anything new recently and have no idea what could be causing it. I've worked on it and here's what I've tried:
When I take the positive battery cable off and put a test light in series from the positive cable to the battery post, the test light is lit up.
If I remove the #6 fuse from under the hood fuse block, the light almost goes out. Then the relay #2 under the dash starts pulling in and out intermittenly until I put it back in. If I pull the relay #2 and the #6 fuse the test light is almost out- very dim.
The truck does have a rust resistor box (been there since purchased) that puts a charge on the chasis. So, I'm assuming that is why the test lamp is very dim.
The #6 fuse is for the audio system. It does have a Ford CD changer added and installed behind the seat, but that has been there for years also.
Please help!!!
Thank you!
Heather
Any non-stock modifications that could influence the problem?

 

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Pull those two items and then see what doesn't work in the truck. If it is just the radio, I would unplug the cd changer and see if the light goes out. You can then unplug the radio to see if it goes out. I am not familiar with a relay in the radio circuit though, so I am suspicious there is something else on that fuse.

Most trucks fuse the radio in two places. One is a hot all the time fuse for the memory, and the radio shares this sometimes with the courtesy lamps.

The other fuse is hot in run or acc. The radio sometimes shares this fuse with the cruise control.

 

Dave,

Thank you for the info!! It was the radio. I probably have to replace the radio or is it possible to put a switch on the hot side of the radio? If not, any ideas on where to find the factory radio besides ebay?
Thanks,
Heather

 

If you find the one wire that is causing the problem, you can certainly put a switch in there if you don't mind remembering to turn it off all the time. I am assuming it is going to be the hot all the time wire, which will make the radio lose it's memory all the time if you switch it off.