How to Wire Bosch Starter Motors

Written by stephen benham
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How to Wire Bosch Starter Motors
Starter motors usually only have two terminals to wire so the process is moderately simple. (Vintage Car Engine image by itsallgood from

Bosch starters are powerful motors that use substantial amperage produced by a car battery to turn over a car engine. Bosch starters are moderately simple to wire as they only have two terminals. One terminal is wired to the high-power positive battery cable, and the other terminal is for the solenoid and feeds to the ignition system. The circuit is completed as the starter motor is bolted to the car engine and has the battery's negative cable attached to it.

Skill level:

Things you need

  • Protective gloves
  • Adjustable wrench

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  1. 1

    Put on a pair of rubber gloves before you wire your Bosch starter motor. The area around the starter motor gets dirty as it's positioned near the base of the engine.

  2. 2

    Use a wrench to disconnect the negative battery cable from the negative battery terminal. The cable is black, and the battery terminal is marked "Neg", or sometimes has a plastic black ring on the base of the terminal pole. Disconnect the positive battery cable from the positive battery terminal using a wrench. The cable is red and the terminal is marked "Pos," or has a red plastic ring on the base of the terminal pole. Tuck the battery cables away from the battery so they don't accidentally connect while you are wiring the Bosch starter motor.

  3. 3

    Find the two terminals on the Bosch starter motor. Both are at the rear of the starter motor. One terminal is larger than the other. The large terminal is for wiring the battery cable, and the other links to the solenoid and goes to the ignition system.

  4. 4

    Find the two cables near the starter motor. One is a heavy red cable, although you may need to wipe the cable using a cloth to reveal the colour as it's likely to be covered in grease. On the end of the cable is an eyelet. The second cable is not as thick. The colour of the cable varies, depending on the car. However, it is the only loose cable near the starter, so it's easy to identify. The cable has a smaller eyelet on the end.

  5. 5

    Remove the nut from the large starter motor terminal using a wrench. Place the eyelet on the end of the heavy red cable over the terminal and replace the nut and tighten using a wrench.

  6. 6

    Remove the nut from the remaining smaller terminal using a wrench. Place the eyelet on the end of the smaller cable over the terminal and replace the nut using a wrench. Re-check to see that both cables are firmly attached and the nuts are tight.

  7. 7

    Reconnect the positive battery cable to the positive battery terminal. Reconnect the negative battery cable to the negative battery terminal. Start your car to make sure the starter is working.

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