Bad battery? Starter? Starter Switch?

Some contact or connection is corroded and dropping the voltage when the current starts to flow; that dropped voltage releases the relay, the current stops, the voltage rises and the relay re-engages. It happens over and over and casues the chatter.

Places to start looking:
- Corroded terminals on the battery connections
- Corroded connection around the large lug on the starter relay
- Fusbile link erratic or corroded under the insulation
- Corroded connections in the firewall connector