Help Identify part in Volt gage


Help Identify part in Volt gage

Postby jt » Sun Sep 08, 2019 10:54 pm

What is this part highlighted in yellow inside the voltage gauge, what is it's purpose? How does it function? I'm assuming it is to complete a circuit for the two idots lights.
The Blk/Brown wire go to the Neutral light and Oil pressure light.

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Re: Help Identify part in Volt gage

Postby jt » Mon Sep 09, 2019 12:24 am

So after writing the above post and thinking about it, the light bulb went off in my head, Slow thinker :-) . These are the connections that operate the volt gauge.
So how do the the two idot lights come into this, ? Power supply ? I'm trying to get the neutral light and oil pressure light to work on different kind of gauge set.
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Re: Help Identify part in Volt gage

Postby divan » Thu Sep 12, 2019 12:52 pm

Hi, JT. For the volt meter, the black/brown wire is the +12v supply for the meter and the green wire is ground. That much it seems you've figured out OK. As for the "idiot lights" in the part of the wiring diagram you copied -- these are actually the illumination lights for the 3 gauges shown in the instrument cluster: two bulbs each for the tach and the speedometer, and 1 bulb for the volt meter -- they just light up the gauge faces. Note that these bulbs share ground (green) with the volt meter ground, but they are supplied +12v from a different circuit (the brown/white wire).
The actual "idiot lights" you're concerned with -- neutral light and oil pressure light -- are not shown in the part of the diagram you copied. But if you look over to the right of what you copied on the full diagram, you see these two lights between the two turn signal lights. What I think you need to know about these two lights (for wiring a different gauge set -- not sure what you have in mind here, a different volt gauge? or something else?) is that the neutral and oil pressure lights share +12v input with the volt meter -- the black/brown wire -- but not the green (ground) wire. Each of these lights (neutral and oil pressure) are controlled (as to on/off switching -- e.g., completing their circuits through ground) through the neutral and oil pressure switches, which are "grounded" by their physical attachments to the engine (which is ground). The ground return path is through the brown/red wire between the oil pressure light and oil pressure switch, and the light green/red wire for the neutral light.
When the when the oil pressure switch is activated (by low pressure) ground is completed and the light goes on -- it goes off as the oil pressure increases). It's a bit more complicated than this on the neutral light side. The bike has a dual protection circuit that prevents rotating the starter when the bike is in gear: the transmission has to be either in neutral, ¬or¬ the clutch has to be disengaged (lever pulled in) for the starter to rotate. If you look closely at the diagram, you'll see that that light green/red wire runs from the neutral light to the silicon rectifier in the headlight shell and (through a splice) to the neutral switch. The rectifier is connected to the clutch switch by a green/red wire, and the clutch switch is grounded by a green wire. Probably don't need to go into how that rectifier works with the starter motor here (it's "reverse biased", which means it controls the ground path, not the positive path); but basically it means that when the clutch lever is pulled in (activating the switch) the starter has ground and will rotate, no matter what gear you're in; when the clutch lever is out/clutch engaged, the transmission has to be in neutral for the starter to have ground and you have to push the starter button for the starter to rotate.
Long winded response -- sorry -- but the bottom line is that rewiring (for a different set of gauges or whatever) won't matter much if you get it wrong for the oil pressure light (it really is an "idiot light"); but be careful how you mess with the neutral circuit -- it could lead to some nasty surprises when you go to start the bike.
If all you're doing is putting in a new volt meter, then just be sure to use the black/brown wire as it is in the instrument cluster as the positive lead for the new meter, and the green wire as it is for the ground lead for the new meter. If you have to cut wires, just be sure you tap that black/brown wire after its connection to the two indicator lights -- don't cut the neutral light off from its positive feed.
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Re: Help Identify part in Volt gage

Postby divan » Sat Sep 14, 2019 9:54 am

JT -- I may have given you a bit of a wrong impression in my earlier reply. If you're installing a different gauge set it is possible to wire it without including either the neutral indicator light or the oil pressure indicator light. Cutting the neutral light out won't disable the neutral SWITCH -- the switch will still work (disabling the starter when the transmission isn't in neutral) you just won't have the light to indicate that the transmission is in neutral. What I should have said was that you should be careful about wiring around the rectifier, which if altered MIGHT disable the switch, something you probably don't want to do. Sorry for the confusion.
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Re: Help Identify part in Volt gage

Postby jt » Sun Sep 15, 2019 11:48 pm

divan,

Thanks for the great post / info it made me go back and look at some of the changes I made but were working properly before I went down this path with a different gauge setup.
I had upgraded most everything electrical, such a repo wire harness, starter solenoid w/ built in 30amp blade fuse, got rid of all the glass fuses in the handlebar and dual beam headlight, LED turn signals and somewhat newer handlebar switches. CBR Euro style with front exit throttle cables on the throttle side with headlight off, parking lights (Frt T/S and rear taillight on) and finally headlight on. And I used a Euro 94/95 CB1000 on the clutch side as I wanted the index finger Flash to pass switch. But in order to use this switch I had to rework the wiring to make everything work as it should with stock wiring harness, ie.. Clutch switch, horn and signals and as dumb as I am electrical it was slow going for me but in the end it work great.

But as far as the gauge I bought a Chinese LCD digital gauge, now you can laugh :laughing-rolling: ! but hey it looks cool ! It came with no wiring diagram as to which color wire for each function. So I had to dive in again and work through it. After your post I did manage to get the correct turn signals lights to flash, High beam to work, neutral light to work and for a time the Oil light switch which is substituted with Check engine light on the gauge. But today I went out and the Oil / chk eng light will not work. I can make the light come on if I put the Neutral wire to plug it will light up, so I know the gauge light still works. The Neutral/Oil light wiring harness is new as I made it so I would not have to use a old one. So I'm suspecting the oil switch. The engine came with a Tee at the oil switch mounted along with a Pressure gauge, but am kinda scared to remove it as I'm worried the threads in the case maybe be damaged. So I will use the oil pressure gauge for now. So for the Tach input I will be using the Ignitech ECU and it will supply the input for the tach, I HOPE ! :handgestures-fingerscrossed: but that's down the road a bit.

Anyway thanks for the fuel for though great of you to chime in as my original post was vague at best, I was tired of going over the schematic so much when I came for the night. I think I will have one blown up a size or two to make it easier to follow through !!!!!!! LOL

Now to figure how to mount the dash.
Thank you again !!

Booting up
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Re: Help Identify part in Volt gage

Postby divan » Sat Sep 21, 2019 4:06 pm

Glad I was able to help a bit, JT. That's a VERY interesting mod you're working on. Have you actually started the bike yet, or are you still in the development stages, testing your re-wiring?
As far as the oil pressure switch: you report that the light initially came on when you tested it, but subsequently didn't come on in later tests. As long as you didn't do any changes to the wiring between tests, this suggests a couple of possibilities. Since the light still works when alternate power is supplied to it, it's not the bulb. So it's either something that's come loose in the wiring or connections between the light and the switch or, as you suspect, the pressure switch itself. Since the pressure switch works through resistance (not mechanically) it's possible to short them out. An easy way to test the switch itself, before digging into the wiring, is to use an external test light. If you don't already have a test lamp,get a 12 volt low watt bulb (a working bulb from your old instruments will do). Solder a wire to the bottom/+ post and solder a second wire to the side of the base (-). Remove the harness lead from the pressure switch. Use your battery (disconnect both harness cables 1st and just use the bare battery posts for your test) and touch the (-) ground lead to battery ground and the (+) lead to battery positive. Or you could also just use a 12v power supply or flashlight batteries, etc. If the pressure gauge is good, the test lamp will light.
Before you tear into your harness, you could confirm the problem is there by simply running a jumper wire between the pressure switch terminal and the positive terminal on the indicator light in your gauge set. Make sure the jumper isn't shorting to any other wires and turn the switch on. If the indicator lights, the the problem is in your harness.
Hope this helps. Please don't use this test procedure on the neutral light circuit. As I explained earlier, this circuit is wired differently and you could damage the rectifier.
If the switch tests OK, then the problem is likely in your wiring harness. One other thing to check. My '79 also has the T-gauge-switch set-up, and the T actually raises the top of the switch (where the wire connection is) up very close to the aluminum carb rail on the left side. If the rubber boot is worn or missing, or the insulation on the wire is bad (a common thing on these bikes since the wire runs in close proximity to engine, which bakes the insulation and boot and they eventually fail) you could have an intermittent short at that point. Check that too.
All this of course is if you want to have the indicator light. Since you have the pressure gauge you could run without the light. I like to keep both, but in reality that switch only comes on ( acquires continuity, so the light comes on) at 2.8 PSI. If you're riding and losing oil pressure gradually (not a sudden total loss of pressure), then by the time the light comes on your engine will be toast anyway.
Here's an amusing anecdote of what can happen -- it's why I installed the gauge and check it regularly while riding. About 25 years ago, shortly after buying my '79, I did an oil change. Started the bike in the garage and wheeled it out into the drive, preparing for a ride. Suddenly, the pressure light came on. I shut the bike off and saw an expanding pool of oil on the driveway. I'd forgotten to tighten and torque the oil filter bolt. We all learn by our mistakes.
Happy wiring.
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Re: Help Identify part in Volt gage

Postby jt » Sat Sep 21, 2019 11:55 pm

divan, Yes I've started the engine and ran it but did not have gauges on it then. Oil pressure was good at 55psi at least I think that is good. I will try to check the oil switch and the sub harness for the oil & neutral light, I made up a new one for this to go with the new main wiring harness. Thanks for all the help. More to come down the road.

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