There are many car operations that we’re so accustomed to that we don’t think about until they do not happen as we expect them.
Take for instance, when you turn the key in the ignition switch to the ON position, you only expect the dashboard lights to come on and nothing else, right?
What if the car starter engages at that point and not when the key is in the START or RUN position? Why does that happen? Is this a fault you can fix yourself and if so, how?
This post lists possible reasons why the car starter motor engages in the on position instead of the START or RUN position and suggests fixes you can do to get it working properly.
Quick Answer
If the car starter engages with the key turned to the on position, this can point to a probable fault with the ignition switch or a wiring fault in the wires connecting the ignition, starter relay, or starter motor solenoid.
Read on for details of this, other possible causes, and what checks and fixes you can do.
Tip: If you can, get a wiring schematic and a multi-meter to guide the troubleshooting. It will save you some time.
Why Car Starter Engages with Key in the ON position (+Suggested Fixes)
Here are some possible reasons why a car starter can engage with the key in the ON position.
#1. Wiring problem. Check for a short or a crossed wire connection especially if you’ve made a modification or replaced a car starter or ignition switch.
Could you have interchanged the wire connections to the ignition switch? This too can cause the starter to engage when the ignition is still in the ON position.
If so, double-check the wiring. The starter relay should only be hot when the ignition is set to START position. Use the schematic and multimeter to confirm that you’ve made the right wire connections.
There is likely to be 12V supply to the starter relay even when the ignition is in the ON position. Follow this supply (using a schematic, follow this 12V supply wire to get to the likely cause of the fault condition.
#2. The ignition switch is faulty. Is the ignition switch supplying 12V to the starter relay regardless of whether it is set to the ON or START positions?
Check this by turning the ignition switch through various positions while measuring the output voltage.
If the switch supplies 12V in both positions, then you probably have a fault with the ignition switch. Swap it out with a known good quality switch and check if it clears the issue.
Note, though not common, it is possible to find a new replacement switch faulty too!
Is it a Fault with the Starter Relay?
A burnt-out starter relay is more likely to result in the starter motor not engaging at all regardless of the ignition switch position.
Do not hesitate to contact a qualified auto mechanic to support you on this.
Why it is Bad for the Car Starter to engage with the ON position
There is a risk that the car starter remains engaged even when in the START position causing prolonged cranking of the engine that damages the starter pinion and ring gear teeth.
Closing Thoughts
If the car starter engages with the ignition switch in the ON position then it is likely that there is a wiring fault or the ignition switch is faulty.
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