Wiring Woes - T100 To M-unit Blue

My 03 Bonneville and I are having some difficulty. I’ve completely striped the bike in order to fit an m-unit blue: with this am intending to rewire the entire bike. This is proving more difficult than I had hoped.

is anybody able to tell me what the ecu actually does on a 2003 bonneville? This is a carburettor engine, so I struggle to see the relevance of an ecu. Am I able to do away with this entirely? What issues would I face without it?

Has anybody rewired an 03 bonneville? If so I’d love to hear from you or anyone with wiring experience.

 

Yes hence the name - in control the ignition how does it operate?

 

Sensors for vacuum? This seems way too advanced for a carburettor engine. If the intake is delivered by carb what is there to monitor?

 

I’m just trying to get my head around the reasons for the piece of kit.

 

Yeah, they have some great videos. Unfortunately the wiring of the unit will be incredibly straight forward. I’m trying to find out what I can dispose of on the original/factory loom/circuit. The videos I’ve come across aren’t bonneville specific, so no telling how important or how to dismantle the factory ecu.

 

That’s exactly what I thought. Given its mechanical operation there can’t be too much tech involved - also, once set, would it run on the last setting if bypassed? I’ve found some terrible wiring and really poor connections.

 

https://purposebuiltmoto.com/motorcycle-electrics-101-re-wiring-your-cafe-racer/

Also worth a look, if you’re in need.

 

On further investigation I’m unable to detect what my ECU does other than manage some electrical controls. The engine has very little cable/wire leading to it. The cables I’ve found and followed are all accounted for. The ecu seems to not much more than a junction box.

 

Absolutely, this was precisely my thought. The chaos within all the connection and spliced connections - If somebodies house were like that, they would be livid. I've located the hazard sensors, if I can locate the timing sensors etc I can do away with the rest of the loom.

 

So, a few days of fiddling around and some reference help from the Haynes dictionary.

Most of the sensors for the original loom are not in use or even attached. Carb heater/s, Alarm control unit, carb vent valve, throttle position sensor, carb thermostat all disconnected and unaccounted for. This may have something to do with the aftermarket carb fitted - hopefully this should make my rewire slightly easier, only time will tell.

 

Well, I have a set of mikuni carbs. As far as I’m aware - no throttle sensor present, however, this could easily be oversight on my behalf. Given I’ve already trimmed the fat (so to speak) of all the redundant and void connections. This I shall double check.

It’s going to be damage limitation on the rewiring as the connections were terrible. I understand that four way switching may be legally required for a market bike but in no way is it desirable.

The ignitor is embedded in the ecu as is the tacho pulse. Most of the crucial devices I’ve managed to locate and have singled out. Now I’m to figure out how abouts I liven them up. Hopefully between the Haynes and m-unit manuals I can decipher an operational way of linking the two.

What would the protocol be for sharing wiring diagrams etc? As I am more than happy to post the 15years worth in the Haynes.

 

So, several months later and I am finally in a position to put the bike together.

Having completed most of the wiring, nows time to fire it up and see what’s going to happen. Except every time I hit start I hear the starter motor but I’m fairly certain I’m not getting any spark. I’ve no idea why that may be.

Any advice would be appreciated.