Hi everyone,
I have a 2017 Softail Slim. I am having an electrical issue. I just replaced the original battery. The bike wants to start as soon as I connect the positive terminal with the ignition switch in the off position and the switch off on the handle bar. I disconnected the switch on the handle bar and it still wants to start. Thats all ive done so far.

 

Are you saying the starter motor engages and starts cranking the engine over?
That's often a matter of a stuck starter solenoid. You can often release the solenoid by rapping on the starter motor itself with a hammer or such.

 

That's what I figured. I'm hoping that I can get it to disengage by rapping on it. I'll post again once I get a chance to work on it.

 

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Just be aware that once it starts sticking, it tends to keep sticking. Unless you take the plunger out and clean it and the contacts. Mmm, make sure you don't have any interesting crud on the shaft or such that would mechanically bind it.

 

So I bought a new starter and I was finally able to get enough time to swap it out ( after removing the battery box and the oil tank). Doing the same thing. I know it's not the switch on the handle bars (took it completely out of the circuit)and it still tried starting. So I'm leaning towards the switch on the gas tank or the ignition module. If anyone has any more ideas I'm open to suggestions. I don't want to throw parts at it.

 

Stop guessing, work smart.
The starter is electrically power and connected direct to the battery, in normal operation all it requires is a 12 volt supply from the BCM to the solenoid for it to start.
No 12 volt from the BCM = No start
Unless there is mechanical issue holding the solenoid in this is the only way it would not require the supply from the BCM as the battery is connected direct to the starter!

You have replaced the starter so lets assume the new starter is good with no issue.

So step one remove the single terminal from the starter Solenoid Wiring diagram [128B]
Reconnect the battery, see if the starter try's to turn, if so you have an issue with the starter.
If not check for 12 volts on terminal 128B,
If so you have a wiring problem and need to work backwards through all the connections until you locate the fault.

If no 12 volts on terminal 128B, try turning the ignition on, if still no turn on the kill switch, if still no then then press the starter switch, this is when you should get the 12 volts on terminal 128B, but only when the switch is pressed with the kill switch on & ignition switch on any other time you have an electrical issue!

 

To add onto what @SJC69 wrote above:

Let's not assume the new starter is fine, let's check it. Disconnect the red/black wire (128B) from the solenoid. Does it still self crank? If yes, then you've a problem either with the new starter motor, or you're managing to install it incorrectly.

But more likely, you are going to see a constant 12 volt at that 128B connector on the starter solenoid. Normally it would be zero volts unless you press the start button to crank over the engine. You need to back trace this constant 12 volts and find it.

Go to the BCM connector L2 de-pin the connector and check the wire and the BCM pin for 12 volts.
If you still have 12 volts in the wire with it unpinned from the BCM, you've a hot short to the wire somewhere in the harness between the BCM and the starter motor solenoiod.
If the wire is dead, but the BCM pin has 12 volts, the problem is either in the BCM or upstream from the BCM.

At this point, I don't see it clearly in the above wiring diagrams, but the bike requires:
1. Power from the ignition switch ; and,
2. The kill switch to be in the run position; and,
3. Maybe the transmission to be in neutral or the clutch lever to be pulled in (if so equipped); and finally,
4. The start or crank button to be pushed.

You need to find each of those circuits and test their operations and their signal to the BCM via whatever other systems or circuitry they go through.

Either the BCM is falsely being told to go ahead and crank the starter motor, or the BCM is defective, and improperly constantly cranking the starter motor. Either are possible.

Don't just check switches for continuity. You need to be looking for voltage signals at connectors and wires. If mice have chewed the wires and the start button wire to the BCM is now shorted to another 12 volt wire, the signal to crank would be constantly sent to the BCM for example. You need to be methodical here in tracing this problem. You really need the wiring diagrams, and I think you can download them for free from the Harley service portal for your bike.