Join Date: Sep 2008
Location: Honolulu, HI, USA
All Bosch relays have essentially 4 pins (if there's a fifth, its tied to one of the four). Internally they can be a little different, but that is mostly beside the point for general troubleshooting purposes.
The relay functions as an electronic switch so that you don't run full amps to the actual switch on the handlebar. Minimizing the length of high-current wire runs is a worthy objective, especially for wiring systems which tend to be exposed to weather as on a bike.
Terminal (socket on the female side or male pin on the relay itself) numbers are 30 (always hot), 85 (ground), 86 and 87. Terminals 85 and 86 activate a solenoid that closes a connection between 30 and 87, thus powering whatever is downstream of terminal 87. The easy way test a suspect relay (or check whether the fault is the relay, downstream device or wiring) is to put a jumper on the relay socket between 30 and 87 and see if the downstream device is activated.
You can also use a pair of jumper wires to ground 86, and put +12V to 85; the relay should audibly click. If you also have three hands or alligator clips, resistance between 30 and 87 should be infinite, than with 85 powered and 86 grounded, the relay will click and resistance should go to near zero.
Pins E, A2 and A3 mean nothing to me, haven't ever seen those on a Bosch relay.