the top right as you you look at it?

It is the 5A fuse.

And when should it light up when testing?

running or just keys on or off, no test light on either side of fuse.

I am tracking down a couple of things.

oil pressure and temp gauges work, so volt reg. should be good, but fuel gauge is always on E, no matter what I do, remove sending wire from stud, place on bullet proof ground at tank, etc. stays on E.

Also, is there a way to test horn relay/relay slots. I can bench test my horn, but in car nothing.

I was thinking if I had the blades of the horn relay most of the way in, I could probe each with a test light and test horn button on steering wheel.

Thank you for any information.

Fuse number 5 IIRC is for the interior lights. This includes dome light/gauge/shifter lights.

I would bench test the sender by making sure it has somewhere in the range of 8-78 ohms of resistance from full to empty. If the resistance is way off (high), this could cause the gauge to be stuck at 'E'. The next thing would be to check the blue wire that connects to the stud on the sender for contunuit back to the gauges and of course, the ground.

The horn can be tricky if the steering column is not grounded well. If you pop the horn pad off, there are two terminals. The red terminal goes back to the relay via the turn signal switch and the black grounds to the column. It is the horn pad being pressed that conencts this circuit.

There should be a dedicated black ground jumper wire that connects to one of the column mounting bolts to the dash frame. This is essential for the horn to work properly.