Odd fuel gauge readings

[3qtrton]

The brake lights 20A fuse on my 1970 C20 has burnt out twice, so I removed a bunch of wires tied together in a ball behind the rear license plate and used electrical tape to tape off the open wires sticking out in all directions. I have to re-do the system to be able to hook up a trailer, but for now I would just like to have working rear lights. Funny thing happened afterwards - the fuel guage needle is sideways pointing to the right hand sector of the guage. Could there by any connection here? I'll have to check the manual to see if I can find a circuit that ties into the rear lights, but is this right sector of the large fuel gauge used for anything? I've had the truck working for a couple of months and the fuel gauge has worked well in the top sector only.

Thanks,

Frank