UnderTheDash.com Relay Index

Relays are a very useful tool to an installer. There are several types of relays, with different functions and voltage requirements.

Primarily, we use the 'Bosch' type SPDT relay. This relay is pretty basic. The relay acts as a switch, but switches by means of 'detecting' voltage instead of having to physically switch it with your finger! This type of relay is very durable, having contacts rated at 30-40 amps, yet is small enough to be tucked away and forgotten!

Below are diagrams for common uses of this popular relay:

Inside a relay

SPDTdiagram.gif (15063 bytes)

Convert 12v to Ground

Convert12vtoGround.gif (10225 bytes)

Convert Ground to 12v

ConvertGroundto12v.gif (5453 bytes)

Adding Accessories

newacc.gif (8865 bytes)

Starter Kill

StarterKill.gif (12356 bytes)

Aftermarket Trunk Release

AddTrunkRelease.gif (10972 bytes)

OEM Trunk Release

OEMTrunkRelease.gif (10115 bytes)

Domelight Supervision - Negative Switching

DomeLightNegative.gif (9982 bytes)

Domelight Supervision - Positive Switching

DomeLightPositive.gif (9699 bytes)

Latching Relay - Positive

LatchingRelay-PositiveTrigger.gif (6825 bytes)

Latching Relay - Negative

LatchingRelay-NegativeTrigger.gif (6904 bytes)

Power Locks - Reversal Rest at Ground

DoorlocksRRG.gif (17310 bytes)

Power Locks - Reversal Rest at Nothing

DoorlocksRRN.gif (21520 bytes)

Simple Power Window or Sunroof Automation

WindowRollup.gif (21255 bytes)

Safely Adding a Second Head Unit

Legend for 4PDT Relays:

1 - Left Front Speaker (+)	5 - Radio 2 LF (+) Output	9 - Radio 1 LF (+) Output
2 - Left Front Speaker (-)	6 - Radio 2 LF (-) Output	10 - Radio 1 LF (-) Output
3 - Right Front Speaker (+)	7 - Radio 2 RF (+) Output	11 - Radio 1 RF (+) Output
4 - Right Front Speaker (-)	8 - Radio 2 RF (-) Output	12 - Radio 1 RF (-) Output
13 - Left Rear Speaker (+)	17 - Radio 2 LR (+) Output	21 - Radio 1 LR (+) Output
14 - Left Rear Speaker (-)	18 - Radio 2 LR (-) Output	22 - Radio 1 LR (-) Output
15 - Right Rear Speaker (+)	19 - Radio 2 RR (+) Output	23 - Radio 1 RR (+) Output
16 - Right Rear Speaker (-)	20 - Radio 2 RR (-) Output	24 - Radio 1 RR (-) Output

Note: The 4PDT Relays pictured above represent Radio Shack #275-214 ($7.99 ea)
You will also need an antenna y-adapter if you want radio reception on both head units.