FI fault light and weird electrics number - Wrist Twisters
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post #1 of 9 Old 07-30-2019, 07:01 PM Thread Starter
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FI fault light and weird electrics number

Hey all, I was putting some LEDs on the bike, hoping to get a little more sideways throw. Install went fine, lights worked fine, bike ran. Cleaned up the wires a bit, bike started throwing the FI light and refusing to start or prime the fuel pump. Had this before when the bike thought it was being stolen, so checked the pink wire under the seat. Voltage of 8.7-8.8, which seems weirdly low. Battery is charged as per the charger. Checked the wires coming out of the ignition; I have the green wire, one red, one black, and one white and black. Red and black read 12.something, but the white and black wire reads the same 8.7 or 8.8. Is this the diode being blown? One of the fuses on the LEDs, after I took them off, was blown, or at least looked blown. Replacing that fuse didn't change things, and from what I can tell the fuses underneath the seat look fine. Ground wire from the tank has been fine and I didn't interfere with it to get the lights on. Any ideas?

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post #2 of 9 Old 07-30-2019, 07:25 PM Thread Starter
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Took the cover off the ignition and measured from the source, as it were. Voltage going into the diode is 12.7, only 8.7 coming out. So partially failed open, dropping the voltage too far? Anyone got a good source for these stupid things?

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post #3 of 9 Old 07-31-2019, 12:13 AM
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Good luck with this. I'm a novice when it comes to chasing electrical gremlins.Only just got myself a multimeter.
Am a keen student so be good if a knowledgeable sparky chimed in.
I do remember reading a thread here somewhere on that ignition diode.

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post #4 of 9 Old 07-31-2019, 01:00 AM
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Calling Rob Tharlson..

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post #5 of 9 Old 08-03-2019, 12:51 PM
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Most all of these weird electrical issues that start all of a sudden usually end up being a bad battery. I would start by taking the battery to an auto parts store and have it load tested. Just because the battery is charged and reads 12V, it could still not be able to start the bike.
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post #6 of 9 Old 08-07-2019, 10:17 AM Thread Starter
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Battery is reading 13 and some across the terminals, when the bike is off and when it's on. The diode was suspect so I took it out, and I'm measuring the voltage into the pink wire, #19 on the gray connector, with the meter. I couldn't find the exact diode Honda uses, of course, so I grabbed some that are kinda close in value. Rob said elsewhere that the voltage into that wire needs to be between "10.5 and 11 volts," so it's a pretty pissy little thing. Off to the electronics shop.

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post #7 of 9 Old 08-09-2019, 12:50 AM
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Originally Posted by draco880 View Post
Hey all, I was putting some LEDs on the bike, hoping to get a little more sideways throw. Install went fine, lights worked fine, bike ran. Cleaned up the wires a bit, bike started throwing the FI light and refusing to start or prime the fuel pump. Had this before when the bike thought it was being stolen, so checked the pink wire under the seat. Voltage of 8.7-8.8, which seems weirdly low. Battery is charged as per the charger. Checked the wires coming out of the ignition; I have the green wire, one red, one black, and one white and black. Red and black read 12.something, but the white and black wire reads the same 8.7 or 8.8. Is this the diode being blown? One of the fuses on the LEDs, after I took them off, was blown, or at least looked blown. Replacing that fuse didn't change things, and from what I can tell the fuses underneath the seat look fine. Ground wire from the tank has been fine and I didn't interfere with it to get the lights on. Any ideas?

Er, how *exactly* did you wire these up? Did you run fresh wire from the battery to the lights and control them via a relay/switch or what?

1986 Honda Nighthawk 700S
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post #8 of 9 Old 08-21-2019, 04:18 PM Thread Starter
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Alright, in the interests of spreading good info here, it was the fuckin' tank ground. Had nothing to do with the lights, somehow, unless having a bit more load was just too much for an already crap ground. I replaced the ground with a larger gauge wire, ground away some of the crap at the contact points with sandpaper, started right up. However, things I learned:

The board will happily turn on at 8.5 or 8.7 volts; I'm reasonably sure that the actual acceptable voltage is just <12v.

You can replace that bullshit diode at Mouser, they're like $.35 a pop. If you're screwing around with the ignition, this can either be soldered in at the normal spot, or at the back of the bike, going into the pink wire. The board doesn't care which.

If you want or need to re-key a 919, the best way is to order the base contact portion of the ignition from Partzilla, here. This will get you the correct, US ignition base, with the right wire setup and the diode already in place. This can be mated easily to any of the 919 keysets from China, available off eBay or wherever. This is not hard to do, but is pretty annoying. I'ma make a post on just that bit, I think.

You can also make an Asian-market 919 ignition work by splicing in a diode. If you open up the butt of your ignition and don't see a pink wire at all, you have an Asian-market ignition. If the diode fails, or just isn't there, the bike will throw a FI light and refuse to prime the pump. You won't get any blinking error codes or anything.

Taking apart the entire ignition is something I would now recommend at like 20k. Mine was filthy at 40k, bad enough that it was grinding internal parts. Note that there are a few springs that you will want to keep track of, and note that the plates in the actual cylinder can and will fall out. Make sure that, if that happens, you test to make sure you have them back in the right order. This is what lets your own key turn the cylinder.

Last but not least, do not in a million years trust the insulation color of a wire to tell you what it does. Test with your multimeter, or at least one of those 12v circuit testers. The switch for the HF lights I got was wired as white-hot, black-ground, and blue-neutral return, which would have at a minimum blown a fuse if I hadn't checked.

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post #9 of 9 Old 08-21-2019, 06:20 PM
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Good call on the tank ground and ignition.
I might clean mine both.

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