Everything you need to know about using your OEM switches with an m-Unit
By their very nature and their relative age OEM switches are not ideal for m-Unit installations but they can in some circumstances be modified to work though they may operate differently than originally designed and require fiddling to switch between functions.
If an OEM switch can be likened to a light switch that completes a circuit when closed a button or switch connected to an m-Unit would be like a key on a keyboard which sends a signal to the computer that interprets that signal and activates the corresponding function. When pressed,the switches complete a ground that is interpreted by the m-unit which activates the appropriate accessory. So the OEM switches must be rewired so that they complete ground circuits when activated and depending on their construction this isn’t always possible.
Considering that the 20+ year old switches are often the source of electrical gremlins due to dirty, worn out contacts and if the reason of installing an m-unit is to have a bike that is as reliable as possible then using high mileage OEM switches may be working against you. Then again, if your looking to maintain the original factory appearance you may want to trade some reliability for the right aesthetic.
What follows is a general run down of the various OEM switches and how to incorporate them into your system. Momentary push buttons like the starter and horn should be pretty straight forward in that they do not require any modification so they will not be covered here.
Stock Controls with separate Hi/Lo On/Off headlight switches:
The OEM Hi/Lo switch can be modified using the diagram in the manual, also shown below. When using the OEM headlight switch you do not have the option of turning your headlight off, you can only cycle between High and Low. There is one relatively simple work around, but it is not ideal. If you run the headlight output from the m-Unit to the light on-off switch, and then on to the headlight you will get the functionality of all the switches, the one drawback to this is that now you are actually running power through the handlebar switches (the way it was originally designed) and that defeats some of the benefit of having an m-Unit. If it is important to you to be able to turn off the headlight this is probably the best way to do it using OEM style controls.
3 Position OFF/ON/OFF Kill Switches & the m-Unit:
The 3 position Off/On/Off switches found on many vintage bikes will inherently not work with the m-Unit but if you are committed to using the OEM switches there is are ways to work around it.
The OEM function operates by closing a positive 12v circuit in the ON position and opening that same circuit in the off position. In order to activate the m-Unit Kill function the switch needs to send a ground signal to the m-Unit when switched to the off position.
3 different approaches to dealing with this switch:
- Ignore the kill switch and program the m-Unit so that you can double tap the start button to kill the ignition.
- Wire the Kill switch so that it interrupts the power to the coils. The issue here is that you have 12v running through the switch creating the opportunity for gremlins the m-Unit normally allows us to forego.
- You can wire the kill switch into a relay so that you're routing the power around the switch.
- AUX1 OUT to Switch as shown below.
- The OFF Positions are open circuits
- The ON Position is a closed circuit providing power to pole 85 on the Relay.
- Relay Pole 86 goes to ground
- Relay Pole 30 Goes to ground
- Relay Pole 87 is open
- Relay pole 87A goes to KILL Input on m-Unit
When the m-Unit is switched on power from AUX1 flows through the switch maintaining an open circuit on the kill switch circuit. When you break the AUX1 circuit by switching to the off position it the Kill Switch circuit is closed providing a ground signal to the Kill Input.
OEM Turn Signal Indicator Wiring:
Unless you have an auto returning switch you'll need to manually flip the switch back. Returning the switch to the neutral position will not affect the flashing of the light and the signal will cancel itself after the alloted time you have programed into the system.