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my 400 fa Honda has all but died, electrics would cut out green neutral light flickered then went lights and horn would work, now horn only only word, will turn over by bridging coil but no start and no lights ot any sort| time to cut loses and scrap???
 

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houll , read what you wrote and try it again , doesn't make too much sense -------- sound like a low voltage battery or bad connection
 

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yea sorry for poor description( writing in English, thinking in a Shetland accent) there's plenty power in battery, but can't seem to find any loose /broken wires, don't understand why only horn works, thanks for the quick reply, houll
 

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Have you checked the fuses?

Is the wiring harness in good original condition (not cut, spliced, taped up or "fixed" in any way) and all of the wiring harness plugs free of corrosion and tight? Take the fenders off and unplug/plug in each one to be sure.

Check and clean both of the ground cables connections where they ground to the motor and to the frame.

What year is this machine? Do you have the service manual for it?
 

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think it's 04 ,no manual and captive nuts on carriers/bull bars spinning round and difficult to get to, earth cables ok, will persevere and see how I get on, many thanks for now, houll
 

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I have a very similar bike , the 2002 TRX450FM , in the fuse box is a diode , it looks like a fuse , when I got the bike it was missing from the fuse box and the P.O. have some jumper wires run to a toggle switch , I cut all that crap out , got a diode and got it back to stock , I really don't know the purpose of the diode , but I would bet you have one in there , you can test it with a OHM meter , one way would show continuity and reversing the probes it would show nothing ---------really don't know if that has anything to do with your problem , just throwing it out there
 

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quad

after kind engineer took pity on he traced fault after several bypasses to ignition switch!!! she is now to be sold!! problem solved!!!!
 

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I have a very similar bike , the 2002 TRX450FM , in the fuse box is a diode , it looks like a fuse , when I got the bike it was missing from the fuse box and the P.O. have some jumper wires run to a toggle switch , I cut all that crap out , got a diode and got it back to stock , I really don't know the purpose of the diode , but I would bet you have one in there , you can test it with a OHM meter , one way would show continuity and reversing the probes it would show nothing ---------really don't know if that has anything to do with your problem , just throwing it out there
I may be but I believe a diodes purpose is to make sure power only goes in one direction? I maybe wrong. In any case I would follow what fish files has said, he sounds like he's worked on a bike or two.
 

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I have a very similar bike , the 2002 TRX450FM , in the fuse box is a diode , it looks like a fuse , when I got the bike it was missing from the fuse box and the P.O. have some jumper wires run to a toggle switch , I cut all that crap out , got a diode and got it back to stock , I really don't know the purpose of the diode , but I would bet you have one in there , you can test it with a OHM meter , one way would show continuity and reversing the probes it would show nothing ---------really don't know if that has anything to do with your problem , just throwing it out there
I may be but I believe a diodes purpose is to make sure power only goes in one direction? I maybe wrong. In any case I would follow what fish files has said, he sounds like he's worked on a bike or two.
you are correct on how the diodes work.
 

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the way diodes are used in different applications can be a tricky thing , last year I worked on a Takeuchi excavator that the owner admitted to having hooked the battery up backwards and after hooking it up right , it then kept blowing a fuse and wouldn't run , it had 3 diodes in it after swopping one it quit blowing the fuse -----then I have seen a lot of machines that have factory add on diodes on the alternator that when they go bad the engine will not kill by the ignition switch , because of feedback from the alternator to the kill solenoid

I said I don't know the purpose of the diode , and would like to , does any one know what it does on the 450 , ok we know it lets voltage one way , that's not the answer , I know it ties in to the neutral light , ICM and the stater ----I am curious cause I got one , I ought to go pull that diode out and see what happens or doesn't happen
 

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the way diodes are used in different applications can be a tricky thing , last year I worked on a Takeuchi excavator that the owner admitted to having hooked the battery up backwards and after hooking it up right , it then kept blowing a fuse and wouldn't run , it had 3 diodes in it after swopping one it quit blowing the fuse -----then I have seen a lot of machines that have factory add on diodes on the alternator that when they go bad the engine will not kill by the ignition switch , because of feedback from the alternator to the kill solenoid

I said I don't know the purpose of the diode , and would like to , does any one know what it does on the 450 , ok we know it lets voltage one way , that's not the answer , I know it ties in to the neutral light , ICM and the stater ----I am curious cause I got one , I ought to go pull that diode out and see what happens or doesn't happen
It is my understanding that the function of the diode that is near the starter is to block an induced high voltage from the starter that occurs when the starter is shut off. If that induced voltage were allowed to enter the system, it would blow the ECM. I don't think you want to remove that diode and see what happens.
 

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Ok ,tells me something -------- when I got the 2002 trx450fm there wasn't a diode in the fuse box and if I remember right they had 2 wires tapped into the ignition and the cooling fan to a toggle switch , you had to turn the key on , flip the toggle on , then it would start , run and the fan was always on ----I found out about that diode by accident while reading the manual , replaced the diode and cut the wire to the ignition and the fan , the engine stated and ran but the fan never would come one , ran the toggle switch to the fan , would like to get it back to automatic again one day , think I need the fan control box
 

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^^^^ What ktriebol said ^^^^

Its a weird phenomena for sure and its difficult to explain all factors and conditions completely, so I'm not gonna try. Its electrical theory/behavioral stuff involving math that can cause anyone a migraine... and I hate math. I could relate an example to help simplify a general understanding of it for most folks, but that wouldn't provide a precisely correct definition of conditions either, so its best left to remain as clear as mud at the bottom of the Mississippi. :) I doubt if I understand it completely anyways.

Diodes are generally used just like you think though. They are like one-way check valves in most simple applications of them. In DC circuits they are used to block AC, from either peak (half-wave), or both peaks (full-wave) of AC sine waves. So, since they can be used to block either peak of an AC sine wave, sometimes the reason(s) for their presence in a circuit isn't very clear.

For example: my 350D has a small diode in the wiring harness that runs from the negative leg of the neutral light indicator bulb, down to the neutral light switch, where that indicator bulb gets its ground that makes it light up when the bike is in neutral. The reason(s) why the factory put a single diode in that simple ground leg for that light bulb may not be clear at first thought. Until you follow that circuit back through the Ignition switch and notice that the CDI also connects into that same neutral light circuit. So that tiny diode serves to block high frequency AC "noise" (noise = AC sine waveform can be "seen" in the circuit (by the CDI) even though AC current can not flow in that circuit, due to the opposite half of the sine waveform being blocked/converted to DC in the regulator/rectifier) existing on the ground plane half of the alternator while the motor is running. Also, think what could happen to the CDI if a specific regulator/rectifier diode shorted on the opposite sine peak... and that tiny diode on the neutral light didn't exist...

The above example is real... and I didn't figure my 350D out right away.... The previous owner had cut that diode out of the neutral light harness and taped those wires back together. I didn't realize he had done that until I started the motor up that first time after I brought it home. Repeated head scratching and muttering foul language commenced. :)

Diodes are built and rated for current handling capacity. There is always losses in electrical devices, so the voltage is always greater going in, than it is coming out of a diode. Generally you'll see about a 1.5v voltage drop through a diode... they can be used as such a voltage limiting device too.

If you ever wish to let the smoke all out, just overload them. They can either short or blow open when they fail.
 
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