My 96 B2500 dash lights went out after plugging in my phone charger. Fuse box in the glove box has no label so I checked them one at a time. I only found one that was blown. It was in spot #20 and it was a 3 amp fuse. I have never seen a 3 amp fuse in a van fuse box before. I had a spare 15 amp fuse and put it in. Also I read somewhere on line that #14 was for dash lights and needed a 15 amp fuse so I stuck in a new one. STILL NO DASH LIGHTS!!!! What's next???

 

The head lamp switch controls the instrument panel lights. Is it turned all the way down? The manual shows a 3A fuse in fuse block #20. Upstream of the headlamp switch is a 20A fuse in fuse block #3, then a 40A fuse in PDC #14.
Did you plug your phone charger into the cigar lighter? That is powered by PDC #15 40A, the ignition switch, and FB #9 15A.

 

I used a axillary lighter port in a small box under the drivers seat. The one in the dash is disconnected. I removed the fuse from #20 and nowhere in my town could I find a 3 amp fuse. I turned the **** on the lights to double check. One way it turns on the dome light but nothing the other way. Where is the down stream fuse box? All I can find is the one in the glove box and one under the hood near the core support.

 

<Checking> Yup, FB #20 is 3A. Makes sense, it supplies power only for dash lights... the instrument cluster, radio, overdrive defeat, cigar lighter, rear window defogger, heater/ac, rear heater/ac... those lights. Not much juice required.
Check for voltage. Pull the headlight switch out one stop for running lights. Turn full counter-clockwise but do not engage the detente to turn on the dome lights. Pull FB #20 and check for battery voltage on the right pin to a good ground.

No other fuse boxes other than the fuse block next to the glove box and power distribution center under the hood.

If you had a dead short to ground on FB #20, it should short again even with a 15A fuse. Not good. Find a 3A fuse.
No idea what was tapped to get power under the seat (seat belt warning system?) or what effect that might have on the electrical system.

 

No power at #20 AT ANY TIME. It is a conversion van with about 7 lighters and none have power. The dash lights worked until I tryed to charge the phone!!!!