Re: '87 735i Starter circuit help (archive)

my '87 735i will not start by turning the key. However, I can hotwire the starter to the battery and it will run. Igntion switch checks out good, as well as solenoid. What else could it be?

Bobby
photographer@rica.net

BMW used a starter relay that gets grounded through the neutral safety switch on your car. Use an ohm meter to check the ground path of the circuit at the relay itself.
The starter relay is mounted on a bracket behind the drivers kick panel, right along with some other relays and wiring connectors. Look for the tell-tale black/yellow wire coming from it[solenoid wire that goes to the starter motor] as well as a heavy black wire that's the feed from the ignition switch.
You should have a good ground at the brown wire[there may be a secondary color on it, but only one brown/with trace color wire. This applys if the shifter is in Park or Neutral only, all other positions leave the contacts open, so no ground reading at those positions.

If the ground/safety switch checks out, then remove and jump pins #87 and #30 of the relay block/connector. Use the relay as a guide, the pins are marked on the bottom. The starter motor should engage if all is well at this point.
Then you're just looking for the incoming 12 volts from the ign. switch when you turn the key to the start position at the relay[black wire]. I think they just jumpered the coil control side with the same wire, but you'll see when you are checking the circuit out.

Usually it's either the relay that's gone bad or the contacts inside the shifter/safety switch are getting worn. Sometimes with a worn shifter, you can start the car in the Neutral position as the contacts for this place don't get used as much as the Park contacts. I've also seen where you can just lean against the shifter lever with your hand and make the ohm reading come back to a good resistance reading.

Rarely, the "start" part of the ign. switch will get worn out with age. I just changed the ign. switch on my old '85 735ia that had 230,000 miles on the original part[I sold the car 2 years ago to a friend] Good Luck

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