SYSTEM / Electrical System Starter Relay Operation 1. When the key switch is turned to the START po- sition, key switch terminal B is connected to terminal ST. Current is routed to the base in tran- sistor (Q2) through resistance R4 in starter relay. Then, transistor (Q2) is turned ON and current flows to coil (L) in starter relay. Therefore, starter terminal B is connected to terminal C and the starter is operated. 2. After the engine starts, the alternator starts gen- erating electricity and voltage at starter relay ter- minal R increases. 3. When this voltage increases up to 21 to 22 V, Zener diode (Z) is turned ON. Consequently, transistor (Q1) is turned ON.
Then, current to the base of transistor (Q2) does not flow and tran- sistor (Q2) is turned OFF. At this moment, starter terminal B is disconnected from terminal C and the starter is turned OFF. NOTE: Condenser C1 is used to stabilize the op- erating voltage. Diode D4 protects the cir- cuit in case the battery terminals are re- versely connected. S Starter Relay B (1) D 3 L R 4 C R R 2 Z D 2 R 3 (2) (1) C M From Alternator Terminal L Q 1 Q 2 B D 4 C 1 C (2) Starter E BST 12V Key Switch 12V Battery T107-04-04-003 T2-5-8