I have an 02 e150 4.6 triton. Last week after not staring my van for 48 hours, it wouldn't start. Strange I thought. My batterys only three months old. Luckily I have a second backup battery located behind the rear bench. It's activated by holding a toggle switch located below and to the left of my steering wheel. I used it and the van started right up. For the first time since then I went to turn my interior lights on using the head light switch. Thay didn't light up. So I opened my door. Still no lights. Can this be a fuse or can it be the light switch itself? The light switch works properly. Pull it out half way and the parking lights go on. Pull it out all the way and the headlights go on but when I turn it counter clockwise, no interior lights. Opened all the doors, no interior light. So what can it be? A fuse? Or can the light switch have that function (turn interior lights on and off) go bad without affecting the other functions?. Even if this were the problem, should the interior lights still light up when the doors are opened? I'm disabled and can't repair it myself. If someone can give me an idea of what it could be, I won't get taken for a ride when I bring it in for repair. I'm assuming it's either a fuse or the light switch. If it's the fuse, might someone know where it's located? I do own a copy of that repair book one can buy at anyone of those chain auto parts store's. I'm having a difficult time disifering the fuse diagram. HELP!! Thanks

 

Your battery drain is possibly related to the interior lighting not working however first step there will be determining if there is an excessive parasitic draw on your primary battery. That's somewhat easy if equipped with a multi-meter. This YouTube video is helpful walking one through this possible condition:
The interior light condition most likely isn't fuse related--I say this because of the battery drain issue. Its entirely possible the main headlight switch's interior lighting segment has failed creating both situations. However by all means check the appropriate fuse with a test lamp, visual inspection can be misleading.

The fuse is in the Central Junction Box located near the brake pedal, its number is: F2.4 rated at 15 amps. More specifically it would be the fourth fuse from the left side in the very top row of all fuses. This can be a real bear testing with most lights etc since its in such close proximity to other metal parts in the same area---be careful.

FWIW Haynes and Chilton manuals leave a lot to be desired when it comes to most things. I've found spending the slight additional money on gently used factory manuals always pays off, most times in the short term.

I hope this helps even a bit!

 

This is not the first time you have helped me. Your descriptions are to the point ans easily understood by myself who's knowledge of all things automotive is limited. My disabilitie will not allow me to check and or repair the problem. I have a few friends who will have no problem following your sugestions and repairing the malfunction. Thanks again JWA p.s. I will let you know how it all turned out

 

Good to know my yammerings and "thoughts" have worked for some!

Should you anticipate or run into a situation I'd be glad to share my phone number just in case. PM me if that would be something useful.