Q: No electrical power on 1990 Ford E-350

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I have a 1991 Tioga Mantera class c motorhome built on a 1990 Ford e350 chasis. IT has a gas 460 cubic inch engine. MY problem is I have a good chasis battery (been tested) but IM not getting any electrical power. The horn, headlights and all of the other things that shoud work doesnt. Everything worked when I parked it in May. I cant figure it out.
(1) Answer
I would start by checking positive battery cables, should be three wires off the battery pos. cable one goes to the starter one goes to the soloniod and one goes to the fuse blocks,check the one to fuse block .check fuses if you didn't already. theres two fuse blocks one under the hood left side by the ac compressor and fire wall.
the other is under dash board by steering wheel