You say that the generator output is -2.5v. Are you measuring across the
generator itself, generator to some other ground, or generator to positive
on the battery? That is a really odd reading.
Are you sure that your 3 wires to the generator are intact and properly
hooked up? Especially the ground wire -- that is the only one I can think
of that would give anything like what you got.

I think I would take the generator and the regulator to some shop that
specializes in starters and generators (probably the older the shop, the
better the chance that they understand what they are doing) and get them
to test the two items for you. If they test OK, then you can work out from
there.

Other things to look at would include lack of a good ground in your turn
signals or a short in the turn signal system somewhere. They are served
by the same fuse as the amp light.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma