Hi all, looking for info on a 1980 DT175 CDI - bike is new to me, runs; it's been stripped down for dirt/trail riding, the sheathing on the harness cut off and the wires folded and crammed every which way.

CDI (under tank) has a red wire coming out that is connected to a yellow/white wire, which comes from the voltage regulator. This doesn't match the diagrams I have. Anyone know what the red wire should be used for? Could disconnecting it damage the CDI?  There is no red wire coming from the magneto.

Clymer (1979-1981 DT175) shows a red wire running from magneto to CDI, with no connections. The '1980 DT175' Yamaha service manual supplement doesn't show a red wire at magneto or CDI at all.

So, I'm figuring a different CDI has been put in at some point 

More info if it helps:

The CDI has seven wires running connected to it:
BR
R
R/W
B
B/W
B
O

However there are only six wires coming from the mag - no Red - flywheel has 'F3T 251' stamped on it.

BR
R/W
B
Y
G/W
Sb

Any info appreciated - Cheers!

I'm not sure exactly if/when the changes happened to the ignition systems in other countries, but in the USA the 78-79 DT175 had a different system than the 80-81. 
First the "non-ignition" wires coming out of the stator:
The Sb wire (sky blue) is the neutral light wire...  Sb leaves the engine in the stator harness, but has nothing to do with the ignition or charging/lighting systems.

The Yellow/white (or yellow) powers the headlight circuit. Nothing to do with the ignition and (normally) should not be connected to CDI box.  Since it appears you don't have the correct CDI box, it might not run at high RPM if you disconnected the yellow from the red...  I'm pretty sure red is the high RPM source coil, if you unplug the yellow, my guess is it won't rev up very high... or if red is the low speed it won't start)

The Green/White is for battery charging...  also has nothing to do with the ignition system.

78-79 has the following "ignition system" wires coming out of the stator:
Brown - Stator source coil (low RPM?)
Red - Stator source coil (high RPM?)
White/red - Trigger coil
Black - ground

80-81 has the following "ignition system" coming out of the stator:
Brown - Stator source coil (all RPM's)
White/red - Trigger coil
Black - ground

78-79 has a 7 wire CDI box because as mentioned above it has both high and low speed source coils.
80-81 has a 6 wire CDI box with a single source coil. 

78-79 CDI box wires are:
Orange - to ignition coil
Black - to ground
Black/white - to kill switch
Brown - Stator Source coil
Red - Stator Source coil
White/red - Trigger coil
Black - ground

80-81 CDI box wires are:
Orange - to ignition coil
Black - to ground
Black/white - to kill switch
Brown - Stator source coil
White/red - Trigger coil
Black - ground

P.S.  If something doesn't look right, let me know... going by memory and I might have mixed something up.

Oh, and in case it wasn't clear...  it sounds like you have a 78-79 CDI box connected to an 80-81 stator.

It will be for the piggy back high speed coil except 1980 doesn't show it on partzilla but 1979 does #5. Nothing related to regulator should go to the cdi box, but then again maybe i've got things to learn. See what others say.
www.partzilla.com/catalog/yamaha/motorcy...dt175f/c-d-i-magneto

Hi MarkT and RT325 - thank you for the replies -

MarkT, really appreciate the details on the years and the breakdown on what wire goes where and does what - helps alot - I'm going to pull the flywheel to be sure, but I bet you are correct, older CDI with newer stator.

RT325 - did not know that there could be two different source coils for ignition, neat - I can kind of peer through the flywheel but easy enough to pull it to check. If the red wire at the CDI is waiting for current coming in, there's nothing getting to it, the regulator at best is grounding it?

I've only run it around the block a couple of times, not nearly enough to need a 'high speed' coil lol

Thank you again -

OTBMF, I know my reply was long...  I did explain the likely reason the yellow "headlight power wire"was connected to red which is basically because the newer stator doesn't have two source coils...

Someone is using the yellow to power the CDI box high speed circuit

I didn't see MarkT's replies when i did mine & likely thought Marks first post was original poster again--i should read. But that started a whole new train of thought & if the previous owner made it work powering off the lighting coil then man that's interesting--& understandable to a point--how clever is 'that man' & MarkT!!. Be interesting to try it unplugging the pirate wire & see if it runs. I think it'll start & not get past idle with red not activated. I say that because the same thing with my 490 with a dodgy high speed coil so by eliminating it i had to run a simple cdi box from a small Yamy scooter. Worked good.

Ok i'm up to speed now [my high speed coil just kicked in lol]. I just had a thought, wondering if say the lighting yellow puts ot more voltage at revs than the correct high spere coil--which is a quite a small amount of very fine winding compared to a lot of coarse windings from lighting--where was i going--oh yeah so if you strobed it i wonder if the amount of advance or retard variation alters more than what it would with the correct coil.
But wait there's more--if you 'do' mean the pirate wire comes from the regulator--& could be the lighting coil wire but with regulator T'd into it somewhere which would limit it to 7 volts guessing.
That model would originaly have an AC 6 volt regulator into the lighting charging somewhere.
I'm outa here-i think.

Hey MarkT - understood - I had missed that idea, re wired funny for power for second coil - thank you. It is a newer stator, no red wire, only two coils, one for lighting and one for ignition.

Neat RT325 re wiring - I am going to test it as is on some trails in next week or so, but so far I'd be I haven't gone fast enough for the 'high speed' coil. If it seems to work I'll leave as is until I track down a correct CDI, and probably a harness lol

Cheers both for all the help!

It could be that it will run fine with the red unplugged from the yellow, but I doubt it.

Oh, and "high speed" is not MPH... it's RPM. The bike can be stationary and it won't rev up even in neutral if something goes wrong on the models that had the high and low speed source coils. (Or if the low speed coil is bad, it won't start unless you really spin the engine over fast... it will rev fine but die if you let RPM drop.)