How to Wire a Hella 12V Relay

Written by robert sylvus
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How to Wire a Hella 12V Relay
Hella manufactures 12-volt relays that control automotive electrical circuits. (12 volt relais, relay image by Sascha Zlatkov from Fotolia.com)

Hella manufactures 12-volt relays designed for automotive applications. Relays use two voltage sources; a control voltage and load voltage. A user-operated switch turns the control voltage on and off. The control voltage then energises the relay's electromagnet. Once the electromagnet energises, the load voltage enters the relay's secondary circuit and continues on to the electrical device that the relay controls. When installed near the electrical device, the relay shortens the amount of load wire needed, which lessens the load wire's voltage drop. Larger voltage drops affect the electrical device's performance and increase the chances of a switch overload.

Skill level:
Moderate

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Things you need

  • Wire strippers
  • Terminal connectors
  • Lineman pliers

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Instructions

  1. 1

    Strip one-half inch of insulation from each wire that will connect to the relay. Four-pin relays use four wires and five-pin relays usually use five wires. In some applications, five-pin relays omit the fifth wire.

  2. 2

    Slide the circular end of a wire terminal over the stripped end of a wire. Crimp the circular end of the wire terminal onto the wire with lineman pliers. Repeat this process for each wire.

  3. 3

    Determine which wire leads to the switch. Slide this wire's wire terminal onto the Hella relay's terminal marked "86" (see reference 2 under the common pin designations chart).

  4. 4

    Determine which wire leads to a ground source, usually the vehicle's chassis. Slide this wire's wire terminal onto the Hella relay's terminal marked "85" (see reference 2 under the common pin designations chart).

  5. 5

    Determine which wire leads to the electrical device's power source. Often this wire leads directly to the battery's positive terminal. Slide this wire's wire terminal onto the Hella relay's terminal labelled "30" (see reference 2 under the common pin designations chart).

  6. 6

    Determine which wire leads to the electrical device. Slide this wire's wire terminal onto the Hella relay's terminal labelled "87." This terminal turns hot when the control circuit activates (see reference 2 under the common pin designations chart).

  7. 7

    Determine which wire leads to the second electrical device, if equipped. Slide this wire's wire terminal onto a Hella five-pin relay's terminal labelled "87A." This terminal turns hot when the control circuit deactivates. Four-pin relays do not use this terminal (see reference 2 under the common pin designations chart).

Tips and warnings

  • Omit terminal "87A" when replacing a four-pin relay with a five-pin relay. Doing this makes the five-pin relay act like a four-pin relay.

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