Séb;

The AMP light being on slightly is NORMAL. It is caused by the voltage drop across the Fuse 1 resistance as current is drawn (V=IR, Ohms Law * ), and gets worse with time as additional resistance caused by corrosion at Fuse and ALL associated connections, increases this voltage drop.

If you have replaced the fuseblock keeping the wiring of the new Fuse 1 the same as the original, you can expect to have minimized the AMP light glow, but that is NOT necessarily completely off, because there will still (and will ALWAYS BE) be a slight voltage across Fuse 1.

Headlight current does not flow through F1 and so does not affect glow.

If your belt tension and system voltage are OK, the (slight) increased glow at high RPM is very simply caused by the slight increase in voltage and therefore current...and so is normal and nothing to be concerned about!

Your use of the term "acid spray" scares me! This MAY clean up corrosion temporarilly, but ANY acid used on electrical connections, especially if not properly and completely neutralized can and likely will cause new corrosion and problems. I highly recommend against it. Instead, I recommend the use of zinc suspension anti-corrosive paste on mechanically cleaned connections...you won't regret it!

Read Gas-Tight-Joint article and other info on this exact subject at: http://www.intelab.com/swem/gastight.htm

* Read about Ohms Law at: http://www.intelab.com/swem/an_automotive_electrical_primer.htm

Cheers