In my experience it can be due to worn brushes. As the brushes wear to
near the end of their lives they are under less spring tension. At high
rpms the speed causes the brushes to bounce up off imperfections in the
rotating surface that they contact. With less spring tension to hold
them against that surface the brushes can float above the surface and
just skim against the high spots. Then the LEDs flicker or come on.

On our vehicles the brushes are part of the voltage regulator assembly
that is screwed to the back of the alternator. New regulator assemblies
can be bought for $15 and up.

Mark

"Greenamyer, William L" wrote:
>
> Had something happen that was a little weird.  When crusing down the freeway, the Battery LED and OXS LED flickered and at one point came on.  They went right out but it was weird.  Experimentation indicates that at 75mph and over (if it is sustained), this sometimes occurs.  Has anyone seen this type of symptom?  Is it an indication of the alternator diodes being weak?
>
> William