The other day I was driving home, cruising at a constant speed when
suddenly my speedo dropped down to zero and the check engine light came
on. After that, the speedo jumped all over the place, past 100 mph,
back to zero, totally random, and the transmission started shifting
weird, so I figured it wasn't just my speedometer... I unplugged the
connector for the Vehicle Speed Sensor, and now the transmission is
pretty much back to normal, but of course, I still have my check engine
light, and the speedo stays at zero.
Today, I installed a new speed sensor, and I get the exact same problem
- clunky transmission, crazy speedo... So now I think it must be
something else, like wiring or grounds. I've also noticed that
occasionally I my dash lights and dome light seem to "throb", but
that's been happening since before the speedo problem. I've seem other
posts online where others had the same problem, but noone ever said
what it was. Should I be looking at my alternator, wires, grounds, or
is it possible I got a brand new broken speed sensor?
I have no problem checking all that stuff, but hoped somebody would
read this that had the same issue and could save me some
troubleshooting time.

Thanks,
Randy