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SR400 wiring diagram?


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Does anyone have a wiring diagram for a 1998 SR400, Japanese model.

I have several diagrams from different manuals but none matches my bike. I am particularly interested in how the CDI is wired.

The model number on the frame is 3HT8 meaning that the ignition system is from the period 1994 ~ 2000. It is totally different to the other years' systems and, as far as I can find out, only fitted to Japanese models. My frame is a 1JR which also indicates a Japanese market bike. The engine is strange as it is a 2H6, which should be from 1978 but they weren't 3HT8 models.

The models that have the same ignition system are SR400 3HT6 ~ 3HTB, 1994 ~ 2000 and also SR500 3GW6 ~ 3GW9, 1994 ~ 1999.

The differences are:

The trigger coil is on a 2 screw bracket and the colours are blue/white and green/white instead of the usual blue/white and red/white and neither has any connection to ground. The readings are different too, giving me 246 Ohms across the coil instead of the usual 87/16 measured to ground. The trigger coil  is mounted around 4 o'clock, rather than 1 o'clock. I don't believe this can be  a low-speed / high-speed pickup.

The charge coil has 2 wires, red and brown. There is no ground wire. The alternator is standard 3 phase AC.The charge coil reading is 143 Ohms, across the coil, again, with no readings to ground. This differs greatly from published data from all other sources that I have found who all measure to ground with a high resistance, typically around 330 Ohms from each side and only 4-6 Ohms between the wires.

These feed into an 11 wire Denso CDI which is something I cannot find any info on.

I came home one day and switched the bike off and then it would not start again! I started fault-finding and first thing was no spark. I did all the obvious stuff, changed plugs, checked all connections were good etc. but didn't find anything. I read all the horror stories of stators just failing or CDI boxes and was dreading what I would find. I started checking the resistance readings and that's when I found that nothing made any sense. I took off the stator cover but couldn't see much wrong apart from the lack of a ground wire. I didn't have a flywheel puller - in fact I still don't, Covid-19 is holding up my shipment from Webike! - so I couldn't visually inspect the stator. The reluctor strip on the flywheel is huge compared to YT videos I have seen, it must be almost 2 inches long. I did find that one screw had come out of the trigger coil bracket and the coil had moved close to the reluctor, so maybe that was causing my difficult starting at times. I replaced the screw and reset the gap to the recommended 0.8mm but still no spark.

I noticed that the wire to the neutral switch was off. I initially discounted this because someone in the past had installed different gauges and had modified the wiring. Out of desperation, I remade the connection to the contact and the bike started 1st kick! The problem was when I tried to ride the bike; as soon as I put it in gear, the engine stopped. This is kind of logical seeing as how the wire from the neutral contact is just a ground wire. Somewhere in the CDI, I guess, should be a switch of some sort that changes when the engine is running, maybe that has failed? I just grounded the neutral wire to the frame and everything works now - but that is obviously not correct.

From my investigations with my meter, I have found the following connections to / from my CDI:

2 wires from trigger coil

2 wires from charge coil

1 wire to HT coil - which incidentally is branched to the flasher cancelling controller but doesn't seem to do anything.

1 wire in from the neutral contact (the one I grounded)

1 wire out to the neutral indicator lamp (not connected)

2 wires that just seem to enable the CDI. They are connected through the ignition switch but do not get any power, simply make / break the circuit which is how the bike ts turned off.

1 ground wire

1 Black/White wire that (probably) went to the kill switch and through the side stand switch - both long since removed. Not connected.

A lot of other parts on the bike have different colour wires and are certainly not wired as per the diagrams I have. The closest I have found is from an XT550K supplement, published by Yamaha but that is still not 100% correct. Although some changes have been made to the wiring I'd say that it is mostly original.

I have been searching for months now to find electrical info for this model bike but no luck. If anyone has any insights / info I'd be grateful. Every time I contact someone - repair shop, supplier etc. I get the same negative response; 11 wire CDI? "Best try and find a working 2nd hand one"! Megazip do have new ones in stock but for $470!!!!




I wrote above >> I just grounded the neutral wire to the frame and everything works now - but that is obviously not correct. <<

What I should make clear is that I grounded the wire that goes into the CDI that should come from the neutral switch. This wire should come from the switch and is sky-blue. It goes to the same plug as the 3 white alternator wires but then enters the loom as a dark-blue wire and goes to the CDI through another connector further up the line. The sky-blue wire in that connector comes from the CDI and goes to the headlight assembly to feed the neutral indicator. A bit confusing until I unwrapped the loom.

So, I removed the dark-blue wire from the indicator to the CDI from the multiway connector and substituted a wire that I just ran to ground on the frame. The neutral indicator wire I will put straight to the headlight to use in the indicator. Currently, someone has added cheepo aftermarket gauges and has used the neutral indicator light as an ignition-on lamp.

I hope this is clear?

Edited by ColinS2
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Would fitting a later, or earlier system be feasible. Sounds like this cdi is doing a lot more than a normal unit.

The sidestand/ neutral cut out is as a rule a separate unit, it has links to neutral, side stand, clutch and sometimes oil pressure to control if the bike runs/starter operates. 

The neutral light connection makes me think its all built in.

None of that helps I suppose, is switching the system out for a traditional 8 wire unit doable, Lh crank case (ideally complete internally), flywheel, a cdi and some time? Not necessarily a zero cost option but it could be a better deal long term. Maybe buy up a complete motor, you don't need a runner after all just the electrics.

You don't say if the bike is as important to you as breathing or a workaday 10 a penny shi@box. Which depends on how fixed it gets I suppose.

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I am not sure if I could fit a different system due to the flywheel being keyed and the location of the pickup coil / reluctor. I would need some definite info on that before buying anything

I am in Vietnam, so getting another motor is probably out of the question.

Due to the differences in outputs from the stator and pickup coil, I doubt that a normal 8 wire unit will work. According to Rex's the resistance values are quite critical. If I could source a cheap working one, I would try it. One option that I haven't yet tried is to fit a ubiquitous Chinese GV6 dc CDI. It should work, in theory and anyway it is well worth possibly wasting $15 to find out. I wouldn't have to butcher the wiring just have some extra connectors pre-wired so it would be plug and play.

The bike is important as it is my only means of transport other than riding pillion on my wife's Honda Lead 🙂but I am retired so no pressing needs to go somewhere each day.

The bike is running fine just now, starts most times first kick, hot or cold. I have overhauled the wiring loom and found and fixed a lot of dodgy connections but it would be nice to have a proper wiring diagram if I can find one. As I mentioned, I have permanently grounded the CDI connection to the neutral indicator - I think that's how it was running before, just not wired very well and I probably caught the wire with the side stand and broke it without realizing, starting this whole troubleshooting thing!


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As a follow up, I had this diagram posted by a Japanese guy on a SR400 Facebook group.

You can see how different the CDI wiring is. It's only a schematic of the CDI but it looks like a diode may have failed in mine and when the engine runs that connection is not getting grounded and the engine stops when I put it in gear. It may be linked to the missing sidestand switch but then the bike shouldn't start if the sidestand is down anyway.

Whatever the cause, it looks like my grounding of the neutral switch wire isn't going to cause any harm and I will be free to use the wire from the neutral switch to ground the indicator directly, rather than going through the CDI.

SR400-J wiring diagram.jpg

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  • 11 months later...

Did you ever find a wiring diagram for this? Believe I have the same cdi unit I'm trying to use on my 1979 model but wondering what I do with the extra wires and whether any of them needing grounding to get the unit working.

All other wires connected, stator - coil testing fine but no spark :(



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