I'm working on a 87 Z28 with a 305 in it.
I have a problem with no dash lights, head lights, turn signals, brake lights, radio and head lights come on then turn off again, with low voltage one min and then normal voltage the next. I also now have an over heating issue because the electric cooling motor doesn't work. the ecm goes from no voltage to low voltage. The battery is new, and the alternator has been tested at two different part stores, with one reading at 11 volts and another at 14 volts. so am I facing a ground problem, short somewhere, or is the computer the problem? thanks for any help.

11 volts is a no-go ... 14ish is usually about right ... I would check it one more place ... If it's less than 13 , I would certainly replace it ... Also, inspect your belt ... belts deteriorate and sometimes even deveop a kind of "glaze" and will slip on some accessories ... Check battery and other connections ... a multimeter would come in handy for this ... Also, get a Haynes manual for some of the basic diagrams ... some libraries have the book on-hand for loan ... Going full circle, once again, I would definitely verify the operation of the aternaor ( or replace it ) and verify that the drive belt is in good condition and has the proper tension ...