• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Help a noobie on a keyless ignition

Not open for further replies.


New Member
Frist off everything I know about automotive electronics and relays, I have learned in the past week.

My project is adding a keyless passive ignition switch on my 2014 sportster.
Im using a passive car door lock/unlock contoler and 3 12v/40amp 5pin spdt relays. Ive figured out all the wiring.
Going back over my bike's schematics i realized the igntion switch is not as stright forward as i thought.

So 2 questions
1. Using my 40amp relay as a stright replacement for my keyed ignition, do I run the risk of frying my ECM?

2. From my little understanding i have a resistance keyed ignition cylinder, that contols the OFF, ON, RUN postions. How do i retain the both the ON and RUN position without the key cylinder?

Included picture is the factory ignition switch schematics
BK/GR runs lightingand handcontol ground
W/BE is ignition switch input at the ECM.



Well-Known Member
Most Helpful Member
Welcome to ETO!
1) Are you aware that, depending where you are located, modifications like this may invalidate your insurance and make the bike illegal?
2) What will power your proposed circuit when the ignition is 'off'?
3) Relays create nasty voltage spikes when they switch off, so you will need to take great care to suppress those or they might well interfere with or damage the ECM. Relays with 40A contacts are way over the top for your ignition switch functions. From the attached pic, showing the resistor values, it is clear that the switch passes only a few mA to the input of the ECM.
4) I think retaining both Ign and Acc functions (if indeed possible) would need knowledge of the passive sensing circuit of the lock/unlock controller, but I don't see how the passive sensor could provide two different sensing actions/signals. Someone else may have the answer.


New Member
Im in the US, so vehicle modifications are not really regulated. Ignition modifications are not regulated in any way.
My insurence will consider it a "electronic anti-thift device" and reduce my insurance premium.

The way the system works at this point.
The controller is powered by the 12v battery with a 5amp fuse.
When my fob is within 10ft(3m) of the bike, the controller sends a .3sec 12v "unlock" signal to relay 1 (latching), then closes relay 3 and then powers the bike.
Pressing the brakes puts the controller into sleep mode.
When the fob leaves the 10ft (3m) area, a "locking" .3sec signal is sent to relay 2, then unlatchs relay 1. Opening relay 3 and powering the bike off.
After 2mins of the fob out of the area the controller goes into sleep mode. To prevent battery drain.

I choose to use a 12v/40amp 5pin relay because they are available everywhere here. If something were to go bad in the system, i could pick up a replacement very easily. Is too big of a relay going to hurt the system?

The only reason i wanted to keep the ON postion. My bike has to be in the ON postion to do onboard diagnostics.

Could i keep the keyed switch in the circuit, but leave it on the RUN postion, at all times, and have relay 3 wired on the ground side of the switch and contol the power of the bike. Would keep the right resistance to the ECM, also preventing voltage spikes from reaching the ECM? Then I could switch to the ON postion when needed?


Well-Known Member
Most Helpful Member
Could i keep the keyed switch in the circuit, but leave it on the RUN postion, at all times, and have relay 3 wired on the ground side of the switch and contol the power of the bike.
I guess that depends on whether or not the ECM would detect an open ground wire and complain.
Not open for further replies.

Latest threads

EE World Online Articles