http://www.autoshop101.com/forms/hweb2.pdf
Page 9
85 & 86 used to energise relay, allowing flow from 30 to 87
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http://www.bcae1.com/relays.htm
Internal Workings of Bosch relay:
The following diagram shows what those external terminals are connected to on the inside of the relay. When there is no difference of potential (voltage) across terminals 85 and 86 (the coil), the relay's movable contact (connected to terminal 30) is held, by spring tension, against the electrical contact which is connected to terminal 87a (the normally closed contact). In other words, when no voltage is applied the the relay coil, terminal 87a is connected to terminal 30. When 12 volts is applied to the relay coil (terminals 85 and 86), the movable contact (connected to terminal 30) is pulled down/in by the electromagnet (coil) so that it physically contacts the electrical contact which is connected to terminal 87. Again, in other words, if battery voltage is applied to the relay coil (terminals 85 and 86) terminal 30 will be connected to terminal 87. The red dashed line shows the path in which electrical current flows from/through terminal 30 to the contact of terminal 87a when the relay coil is NOT energized.
Regardless of this all I'm saying is 85, 86 can be used from existing cigarette lighter wiring BUT 30 should come from ignition live off barrel, and 87 should go to starter wire, both thicker "27 amp" wire...