Fuel gauge sender problems, glowing hot!!

My brother's bug was rewired and the fuel gauge never worked.
I found the fuel gauge sender unit plastic melted inside the tank.
Replaced it with a tube style one that i had and thought i better check it out of the tank first in cas it got hot too.
Pulled the tube off to look at the internals and its ok when it sits where empty would be but if you slide the float up to full tank the little wires glow red hot.
Everything else checks out, fuel gauge needle works fine etc.
Is this sender a 6 volt unit? Bearing in mind the last sender was a modern leverarm type.
Any other sugestions.

check the wiring
make sure the sender unit has a good ground
and it sounds like there is power going into the sender instead of a wire from the guage.
check the wire going to the sender terminal for power.
glowing red sender in the tank could be a problem!!

Thanks ill check it again.
Yes a glowing wire in a vapor filled tank, KAABOOM! no more beetle, no more brother. I might go and have words with the auto sparky who did this.😠