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Discussion Starter · #1 ·
If I could add one question to this thread. I'm also having spark issues. (when looking down from above) The left coil wires (yellow and black/yellow) have power a solid 10.5 on the multimeter. But the right side (black and yellow and blue) wire, have nothing. The most I can get out of them is a small 0.3 on the mulitymeter. I'm getting ready to just follow the wires and see if it is a bad connection. I doubt that both wires broke. Would these ignition boxes drop just one side? I think the black/yellow wire are both from the same sorce and the blue and yellow come from different sorceress. So I think it is just that the blue wire is not getting power. Any idea on this issue? I really don't want to have to buy new ignition boxes.
 

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1983 Honda vt750 Shadow
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Not sure what bike you have.
Disconnect the ICU and see if the voltages are similar at the coils. One side of each coil should have battery voltage. And if you disconnect the trigger wires the battery voltage should show up on the other end of the coil about the same.
It is just a coil of one wire on the primary coil side and the secondary coil.
 

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Discussion Starter · #3 ·
Not sure what bike you have.
Disconnect the ICU and see if the voltages are similar at the coils. One side of each coil should have battery voltage. And if you disconnect the trigger wires the battery voltage should show up on the other end of the coil about the same.
It is just a coil of one wire on the primary coil side and the secondary coil.
I have an old 85" VT700c
 

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I have an old 1983 ! Get that old classic running !
Yes then there should be black/*********** wire going to each coil and the ICU.
Make sure there is battery voltage on them when the key is on and the kill switch is on, because it interrupts that power to stop the engine.
Measure the coils for resistances, and the wires and end caps.
The rear cylinder coil with a blue wire triggers the fuel pump relay so if you disconnect the relay that it will take it out of the measurements.

Here is a link to the manual so you can study the wiring.

 

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Discussion Starter · #5 ·
I have an old 1983 ! Get that old classic running !
Yes then there should be black/*** wire going to each coil and the ICU.
Make sure there is battery voltage on them when the key is on and the kill switch is on, because it interrupts that power to stop the engine.
Measure the coils for resistances, and the wires and end caps.
The rear cylinder coil with a blue wire triggers the fuel pump relay so if you disconnect the relay that it will take it out of the measurements.

Here is a link to the manual so you can study the wiring.

I already replaced the fuel relay. and when I check the voltage I make sure the bike is ON and the kill switch is always on. I turn the bike of by turning the key. I even test the spark plugs buy taking a metal pick in the empty spart pulg wire and hold it against the cylinder try ti start the bike and look for spark. The Yellow is fine. The Blue nothing. If I take the fuel relay out and bypass it the pump runs, it just runs all the time. I will take it back out and check the voltage on the front coil and see, it might by the relay is bad yet again. What sucks it it was running fine Friday night, but Sunday morning no spark. Battery is good it is on a tender and fully charged holding at 13.6 volts. This all started when the rectifier went up. I lost all power and the bike would shut off. and if I put it on the charger the battery would over charge. Replaced the rectifier and that problem is fixed. Now this.
 

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That may be it, if the relay is shorting out the spark signal. Disconnect it and see it you have spark then.
Hopefully the coil is still ok.
 

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Discussion Starter · #7 ·
That may be it, if the relay is shorting out the spark signal. Disconnect it and see it you have spark then.
Hopefully the coil is still ok.
Well I figure that sice a coil is a coil I checked the yellow on both coils and got spark, so the coil should be fine it is just not getting power from the blue wire. I will pull the relay tonight.
 

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Discussion Starter · #8 ·
That may be it, if the relay is shorting out the spark signal. Disconnect it and see it you have spark then.
Hopefully the coil is still ok.
I really want this bike to run for more than 2 or 3 weeks before breaking down again. I'm getting to not trust it for any length of a ride and that sucks.
Starter relay died, fuel relay died, then the rectifier, now no spark. But when she runs she is great to drive and has a tone of get-up-an-go. She will hold 70 with no real effort all day, at least until something breaks.....LOL
 

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It is for sure a 1985? I ask because the 1983 -84 has a 3rd box called spark unit #2 and it goes bad and you can take it out of the circuit and the engine will run fine. But if you have only 1 ICU then that won't help. Just pondering.
You might check that blue wire from the ICU to the coil and relay.
Maybe it is pinched somewhere and intermittently grounds out.
 

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Discussion Starter · #12 ·
It is for sure a 1985? I ask because the 1983 -84 has a 3rd box called spark unit #2 and it goes bad and you can take it out of the circuit and the engine will run fine. But if you have only 1 ICU then that won't help. Just pondering.
You might check that blue wire from the ICU to the coil and relay.
Maybe it is pinched somewhere and intermittently grounds out.
Found the culprit! The blue wire had come out of the plug that goes into the black box. I re-pinned it and she fired right up. Now I have to double check the drive shaft. It was making a card in the bike spoke sound at idle. I will check the fluid level. This is the first time I have heard that sound. But it was also on the kick stand and I normally always use the full bike stand. Not sure if that would affect anything but I will check it out either way.
But at least she fired right up!
 

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My father always insisted on using the Center stand as well. Turns out it’s there mainly for maintenance purposes. Also, make sure there’re no playing cards stuck in the spokes… 😉
 
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