Odd, since I can turn my headlight on or off with the engine running. I can't quite tell where the unplugged wire is coming from. Is the headlight safety relay the same as the safety relay? I thought the safety relay disengaged the starter when the engine started, or does it do both?
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Cam Chain Guide
- Thread starter NP2650
- Start date
The so called safety relay is actually two relays in one unit. The starter cutout relay and the headlight on relay. The 6v from the charging system kicks the starter relay out, and the headlight on relay in (on).
I have eliminated the battery as an issue. I seem to have a drop in voltage in the system as soon as I turn on the key. When I turn the key on, voltage drops from 12.8 volts to about 11.5 volts. At 11.5 volts, the starter relay doesn't reliably work, hence the starter doesn't fire off. Is does work when I jump it directly to the battery, so I believe that low voltage is the culprit. I took apart and cleaned the ignition switch to make sure that wasn't causing any drop. I then traced the voltage drop to the brown wire that comes out of the ignition switch. Based on the wiring diagram, that wire feeds a lot. Of course in terms of a wiring diagram, I have diagrams for both a 1978E and a 1978SE, and my bike doesn't match either of them, but has elements of both. Interestingly, when I pull all the fuses out the fuse box except for the main feed (red wire), I still get the voltage drop. So, unlike what the wiring diagram indicates, the brown wire must not go directly to the fuse box, but has connections (or maybe a short?) before that. Trying to plot out my next moves. Any suggestions?
IIRC the regulator is in parallel on brown ahead of the fuse box; might try unplugging that and see if it cures voltage drop (might be in the rotor too)
This is the '79 diagram. It's pretty typical of the last 4 or 5 models. Hope this makes sense.
1. power from the battery to the fuse box. It feeds the 20A fuse.
2. power comes out of the 20A fuse and splits
3. is power that goes to the ignition switch
4. is the wire going to the rectifier
So... with the three 10A fuses pulled and the 20A left in place, there's a possibility the rectifier could be drawing power off the battery. Normally there's not power going to the rectifier, this is the charge wire that sends current (rectified to DC) from the stator back to the battery.
So it's a possibility the rectifier is drawing current and causing the voltage drop. That line is live to the battery all the time regardless of switch positions. The only way to kill it is to remove the 20A fuse.
That all make sense?
Try disconnecting the rectifier and see if the voltage drop goes away.
Took forever to find this... 5twins put it in my resto thread. I saved it this time.... 
This shows how power goes through the fuse box.
This shows how power goes through the fuse box.
Jim, both diagrams you posted were quite helpful, especially the second one showing the fuse box. I have a spare wiring harness, so I spent about an hour with it on the bench and figured out what was connected to the brown wire with and without the fuses in place. On mine, as you stated before, the regulator is in parallel on the brown ahead of the fuse box. Now hopefully I can isolate things and see where the voltage drop occurs.
I was bored... sue me.
Feel free to save it.
Feel free to save it.
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Look closer Jeff.... it's damn hard to see, but the connection dot to the regulator is lower. It's on the brown wire coming out of the fuse box. It's one splice that ties both the regulator and the rear brake switch..... the brown lead that feeds power to just about everything.
I'd have to deconstruct another harness to be certain (it's been a year or so), but I'm reasonably sure that splice to the regulator is actually on the brown from the key switch to the fuse box (the schematic has it wrong)
Interesting. I checked and I have continuity on the brown wire from the connecter in the headlight bucket to the connecter at the regulator even when the fuses are all pulled (except the 20 amp red main feed fuse). In any event by isolating circuits I found the following:
I had 12.9 volts at the battery.
When ignition is switched on:
Blue wire from the ignition switch that feeds the tail light consumes 0.2 volts
Regulator consumes 0.7 volts
Ignition circuit (red wire w/ white stripe) consumes 0.5 volts
So all together, this equates to a drop of 1.4 volts, landing me at about 11.5 volts. Obviously, the big drops are with the regulator and ignition circuit. I'm not sure what kind of drop the regulator typically has.
I had 12.9 volts at the battery.
When ignition is switched on:
Blue wire from the ignition switch that feeds the tail light consumes 0.2 volts
Regulator consumes 0.7 volts
Ignition circuit (red wire w/ white stripe) consumes 0.5 volts
So all together, this equates to a drop of 1.4 volts, landing me at about 11.5 volts. Obviously, the big drops are with the regulator and ignition circuit. I'm not sure what kind of drop the regulator typically has.
What I'm finding seems to suggest that is correct.
You could be right... I've never paid attention to that area when I've taken a harness apart.
But if you think about it, that means the regulator is fused only by the 20A main. The regulator uses the brown for voltage sensing and to send a max of 2.5A to the rotor. 20A fusing for that application doesn't really make sense. A shorted regulator would blow the 20A main and kill the whole bike. Surely Yamaha wasn't that dumb?
There's 5 connectors in the bucket that have brown wires in 'em, not counting the key switch. You'd need to know which brown you're looking at to know if that's normal. I suspect it is for most of 'em.... and I'm pretty sure they'll all lead back to the regulator because it's on the main brown feed.
The circles I made are brown wires inside the bucket. The diamonds are splices where the brown wires branch off.
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I checked the brown wire at the 3-prong connection that feeds the ignition switch. That brown wire has continuity with the brown wire at the 3-prong connector that feeds the regulator, and with the brown, red/white, and red/yellow terminals at the fuse box. I checked this on the bike as well as on the spare harness I have. From that it seems that the splice to the regulator is before the fuse box.
You guys might be right. I just find it hard to believe Yamaha would take a component that draws at most about 3A and fuse it with a 20A fuse. And then let a shorted regulator kill the entire bike when the 20A main blows. Allowing the bike to die on the side of the road because the regulator went south... why?
Yes, aside from the headlight, the rotor and coil are the biggest power hogs on the entire bike. Both draw 2.5 to 3 amps each. That's about 30% of the entire electrical system, just in those two components. To be honest, I don't see anything out of the ordinary with what you're seeing.
I'd suggest hooking the meter in series with the 20A fuse and measure amps drawn. You can disconnect parts downstream and see how much power each one is drawing. Might give us a better idea where the power's going.
Which reminds me, why are we chasing power? I forgot what the original problem is.... sorry.
'K... jus' cause it would'a kept me up all night, I looked through some original Yamaha prints. They show the regulator fused off the 10A brown coming out of the fuse box on the '78 and '79 bikes. Here's the '79....
And here's the '78... same way... off the 10A fuse
And here's where my mind exploded. On the '80 and up... those bike with the combined reg/rec, they did indeed take power off the brown coming from the ign switch.
Now what kind of idiocy is that?
So on my bike, an '80SG.... if the regulator fries itself, it blows the main fuse and the whole bike dies. You can bet your ass I'll rectify that this winter.
But for the '78 and '79 bikes the regulator is fed from the 10A fuse coming out of the fuse box.... not the 20A fused ignition brown wire.
And here's the '78... same way... off the 10A fuse
And here's where my mind exploded. On the '80 and up... those bike with the combined reg/rec, they did indeed take power off the brown coming from the ign switch.
Now what kind of idiocy is that?
So on my bike, an '80SG.... if the regulator fries itself, it blows the main fuse and the whole bike dies. You can bet your ass I'll rectify that this winter.
But for the '78 and '79 bikes the regulator is fed from the 10A fuse coming out of the fuse box.... not the 20A fused ignition brown wire.
