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Old 10-09-2013, 07:48 PM   #1
zoom45   zoom45 is offline
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Pissed Diode

Ok motorcycle electrical wizards - Got a 2000 Nomad 1500 carbureted bike. Been fighting an intermittent ignition problem for a long time this year. If you pull the cover off the ignition switch and take it apart, there is a small diode between the gray wire and a contact pad in the switch that does not have a wire connected to it. What is the diode for? If I check it with an ohm meter it reads both ways and I thought it should only read one way. Maybe this is causing my problems. The other day I thought I had found the problem and fixed it. I drove the bike without problems for 70 miles but that afternoon I stopped to see my Mom and when I went to leave, the neutral light would not come on and no fire was getting to the start button. After I trailered it home and started checking wires. I couldn't get the neutral light on till I honked the stebil horn, LOL then the bike would crank up. It seemed there was resistance in the white wire going into the ignition switch. I found the white wire that comes from the start relay was brown for about an inch at the end where it solders to the contact pad in the switch. It appeared to have been hot which made the wire turn brown on the end. I replaced the entire white wire from the contact pad to the connector mounted under the tank. I drove the bike again and it ran great so I decided to ride it to work this morning and when 5 miles from the house it started the intermittent ignition lose again. I just turned around and left it at the house. Could this be caused from the diode?
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Zoom45
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Old 10-09-2013, 07:56 PM   #2
macmac   macmac is offline
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Do you have any passing lamps on this bike?
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Old 10-09-2013, 08:08 PM   #3
zoom45   zoom45 is offline
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Yes but they are wired using a relay and also have an on and off switch on the bar.
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Old 10-09-2013, 08:20 PM   #4
macmac   macmac is offline
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My books don't go back that far, but the wire with the heat has a high resistance connection and that needs to stop. i have no idea where that wire gets power but find that place and find where it goes. When you do run a volt meter across the connections to read voltage drop. You want to read 0.00 dcv and not 0.02. typically anyone who has wired passing lamps thru the key switch will have similar symptoms, and sooner or later will toast the switch.

I do not understand a diode with no path for power. What if anything comes off the back side of that diode? If nothing at all I can't see why it's even there.

You are correct in that a diode will pass current one way and only one way when it is any good. It also indicates that this wire has AC current. I have seen this on a lot of bikes where the alternator is running the head lamp relay, but you say this is a dead end.

I re-read since you replaced the wire still test it. Use a digital meter since it will read either way in a negative if you have it backwards. This means that if you get the power flow direction wrong the meter will read -0.02 say if there is a high resistance still across the first 2 places you can probe. if you KNOW the direction of flow use the red probe ahead on the + side and the black probe on the way to ground or the load.

If then there is still a high resistance the meter will just read what that drop is. no (-)

A reading of 0.00 is what you want to see.
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Old 10-09-2013, 08:50 PM   #5
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Here's the ignition wires that go on the switch and it shows the diode



The white wire gets its power from the start relay that has the main 30 amp fuse. It connects to the brown wire in the switch that feeds the 10 amp ignition fuse in the fuse block. The grey wire goes to the igniter. The grey connects to the white and brown when the switch is in the on position. on the switch chart it labels the wires this way:
brown-ignition, white-battery, grey-ignition, blue-tail 1, red-tail 2
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Old 10-09-2013, 09:13 PM   #6
macmac   macmac is offline
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I can just make out the diode. Is it a diode or is it a transistor? What is it hooked up to?

With the battery off line use ohms to probe the diode ends and the switch case i guess. The photo is a tad rough for my eyes.

i don't know..... I am not sure that is a diode. It might be a transistor being used as a resistor.
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Old 10-09-2013, 09:39 PM   #7
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It looks like a resistor to me.
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Old 10-09-2013, 09:39 PM   #8
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Not sure what it is. My battery died in my meter so I will have to wait till tomorrow to check it. I don't see anything in the manual that mentions it. I found this on another forum which discussed a Kawasaki sport bike ignition switch with a resistor:

No, it won't run at all. It will crank all day long, but never start and run.

You said it was to reduce voltage to the coils "once the bike is running", but it is not that, it is an anti-theft feature. And a bad one at that.

It drops that particular wire to 6v (as I understand it - at least on the P model 7) and then whatever is at the other end waits for 6v. Anything more, or less, or none, and the bike won't start. Anti-theft. No resistor in place, no start. So it has nothing to do with ignition other than as an anti-theft feature.

Bad resistor in place, spotty starting or no start at all.

here's another:
Hey guys I read up some research that theres a 100ohm resister in the ignition switch... the grey wire on the ignition switch is suppose to have 6volts... I have a 1990 zx7 that ran perfectly fine until I lost the key to the ignition and instead of paying $200 for a new key i figured buying a whole new ignition off a parts bike for $20 would be the best route to go but it came off a 98 zx7 and everything works and the motor turns over but im not getting spark... I have a feeling it has something to do with that 100ohm resister... did the older bikes have this? or was it a 12volt source? if anyone knows that would help out alot because then Ill buy a older ignition and not worry about pulling out my voltmeter
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Last edited by zoom45; 10-09-2013 at 09:56 PM.
 
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Old 10-09-2013, 09:51 PM   #9
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Quote:
Originally Posted by ringadingh View Post
It looks like a resistor to me.
agree. It looks like a resistor to me. Diodes, are typically a black cylinder with a single band of color on one end to indicate direction. That "bulbous hourglass" with rainbow stripes is a resistor.
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Old 10-09-2013, 10:06 PM   #10
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I still don't understand the use of a resistor but I found this site for a kawasaki 1500 switch and it says it's a 100 ohm 1/2 watt resister. I guess the bike won't run if it's bad. That may be my problem all this time. I guess I just need a new ignition switch.

http://jobear2.com/ignitionswitch.html

This one shows wire diagrams for an older similar bike and explains how it works:
http://www.justanswer.com/motorcycle...0-running.html

Its an anti-hot wire device that is in the stock switch and all vulcan aftermarket switches, but its not in the wiring diagrams (for obvious reasons:)).
It stops anyone just cutting the igntion wires and sparking them together to steal the bike.
without that resistor working properly, the engine ecu thinks the bike is being tampered with and WILL NOT allow the plugs to spark.

This little gizmo is also the cause of so many bad starting problems on Vulcans. the Vulcan MUST have at least 10 volts on the battery while cranking, to power this device. Less than 10 volts = no go!;);)
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Last edited by zoom45; 10-09-2013 at 10:27 PM.
 
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Old 10-09-2013, 10:33 PM   #11
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This is the ignition circuit for your bike. It has a diode listed.

Attached Images
File Type: jpg ignition.jpg (80.4 KB, 152 views)
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Old 10-09-2013, 10:42 PM   #12
zoom45   zoom45 is offline
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I saw it shows diodes in the fuse block that are sealed. I don't know how you can test them. There is also one for the fuel pump. I think my starting and intermittent ignition problems may be the resistor in the ignition switch. Here's a youtube video on a 1500 showing how a bad resistor can keep it from cranking. I have also had some long cranking problems (spins over but not firing). We may be onto something here that is causing problems for a lot of people:
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Old 10-15-2013, 01:08 PM   #13
zoom45   zoom45 is offline
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I put my ignition switch together again and measured the voltage from the grey wire at the igniter and it was 6.1 volts so that tells me the resistor is working as it should. I rode the bike and it seemed fine but started the same intermittent problem again! I ordered a brand new OEM ignition switch which should be in today. If that doesn't fix the problem I don't know what else it could be but the igniter. I guess that will be the next purchase. I have a buddy with a 99 1500. Maybe he would let me try his igniter before I spend $300 for a new one. Anybody got any more ideas? I give up after this round.

Thanks,
Zoom
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Old 10-15-2013, 02:57 PM   #14
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Grab each of the resistor leads with a pair of needle nose and wiggle them to see if the resistor breaks in half. I've seen more than one resistor with a hairline crack. Work fine one minute and be open the next. Usually only visible under a magnifying glass. Also the solder joint to whatever the resistor is soldered to. Those can fracture as well. Again, usually only visible if you wiggle the lead under a magnifying glass. Both are easy fixes and a whole lot cheaper than a new switch.
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Old 10-16-2013, 09:03 AM   #15
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Hey , That grey wire goes to the igniter box . Check for chaffed wires under rear fender from tail lights .I had it happen to me,shorted wire sent power back to ignition switch backfeeding igniter taking out resister ,and igniter ,It didn't blow any fuses because the wires chaffed through together and just backfed the system sending to much voltage to igniter .You need to see if resister is indeed bad
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