I don't know what model or engine you have but if you follow the positive battery cable from the battery, it will lead you right to the starter.
Sounds like a bad connection on the starter. Unhook the battery cables and then take the starter down and LOOK at the starter wires and make sure there tight and not touching each other.
on ebay search for NEW STARTER CHEVY 4.3L S10 BLAZER, C SERIES TRUCK 99 00 01 02 03 04 & ASTRO VAN this gives you an image.
Look at the lower rear end of engine
Get under the truck. Look at the front of the bellhousing, on the passenger side of the vehicle. You'll see the starter sticking out of the front of the bell housing there.
The 1974 Chevy truck has a mechanical fuel pump with a built in pressure regulator.
Slide in under the truck behind the passenger front tire and look up at the bottom of the engine and you will see it.
my 56 inline 6 is on fly wheel back of engine look thru hole above starter, tdc is a small ball like a bb
it has 1 short bolt and 1 long bolt
1988 thru 1998 look basicly the same.
If you slide under the truck behind the passenger side front wheel and look up at the back of the engine you will see the starter bolted to the bottom back side of the engine.
It will look alright if its the step side bed but will not if its fleetside
The heater core resembles a small radiator.