How do I wire a relay in my system?

[Lee]

5.12 How do I wire a relay in my system? [IDB]

There are two types of relays that are commonly used in 12-volt automotive applications: Single-pole Double Throw (SPDT) relays, which have 5 pins, and Single Pole, Single Throw (SPST) relays, which have 4 pins. Depending on the application, you can use either of these; for remote turn-on leads See section 5.11 How many devices can I attach to my remote turn-on lead? [IDB], an SPST relay is fine, SPDT relays are often used in alarm installations. Make sure that you get a 12-volt relay -- this specifies the voltage required to make the relay "switch."

The connections on the two types of relays look like this:

            SPST                       SPDT
    =====================      =====================
             (87)                       (87)        
         +---------+                +---------+     
         |   --    |                |   --    |     
         |         |                |         |     
    (86) | |     | | (85)      (86) | | --  | | (87a - center)
         |         |                |         | (85 - right)    
         |    |    |                |    |    |     
         +---------+                +---------+     
             (30)                       (30)

Pins 85 and 86 connect to the coil which causes the relay to switch. On both relays, pins 30 and 87 are normally disconnected. When the relay is activated (switched) pin 30 and 87 are then in contact. The difference with the SPDT relay is that in the "normal" state, pins 30 and 87a are in contact.

To hook up a relay (either kind) for a remote turn on, make the following connections:

Pin 30 +12 Volts (Battery +)
Pin 87 Amplifiers' remote turn-on terminal
Pin 86 Head unit remote turn-on lead
Pin 85 Ground
Pin 87a No connection (SPDT only)