1997 Chevrolet S-10 • 250,000 miles  Periodically when I
accelerate my lights will briefly go dim and the volt gauge will
go down Asked by February 14, 2012. Start by checking the
serpentine belt tension. (Please do that with the engine not
running!) Next, suspect a defective diode in the generator. That
will show up as very high ripple during a load test with a
professional tester. You can get a head start on testing the
output by using an inexpensive digital voltmeter to measure
battery voltage while the engine is running. It must be between
13.75 and 14.75 volts.  If the generator is producing very high
ripple, a diode has been damaged by the very high voltage spikes
these generators produce. To reduce the number of repeat
failures, replace the perfectly good battery at the same time
unless it is less than about two years old. As they age, they
can still start the engine just fine but they lose their ability
to dampen and absorb those voltage spikes. That leads to shorted
diodes, destroyed voltage regulato