Truck won't start always

1995 chevy s-10 pickup.4cyl. 5speed.52,000 miles
truck will not start. The motor cranks but will not always start. When it starts all the dash trouble lights and check engine light come on bright when you turn the key to the on position. When it doesn't start the same lights are very dim. Truck will then crank but will not start. When the key is on the fuel pump should run but it doesn't. Checked the voltage at the fuel pump and it was 3volts. But the next time you hit the key it might start. Maybe a bad ground somewhere not allowing full power to the electrical system? This one has me stumped any help would be appreciated. Thanks.