89 Silverado 3500

Use a digital multimeter across battery posts, have helper turn key to crank, Does the reading drop, how far? Does the reading not drop at all? Did you check for voltage at fuses? Some are hot all the time, some go hot with key on, check them both ways. Use a test lite. Grounds are important, also, chassis ground--engine ground--battery ground. Pick any component that doesn't work and is fuse protected, I'll try to post wiring diagram? The diagrams in my database for your model year, isn't great. At the starter motor, two voltage circuits, one comes from battery, hot all the time. A smaller circuit goes hot with key in the crank position. The starter grounds through the engine block.