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D T 175 A .head light ?

  • jez
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D T 175 A .head light ? was created by jez

Hi Fellas, i am getting close to finishing my restoration project of this 1974 DT 175 model A . the rear light works with the light switch on and ignition on but no engine running but no head light.with the engine running the head light does not work either , all bulbs are good ? should i get 6 volt at the yellow wire in the head light bucket from the alternator with engine running ? any help would be great. thanks. Jez...
16 Sep 2023 05:37 #1

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Replied by MarkT on topic D T 175 A .head light ?

There's a yellow/white out of the stator that goes to the left handlebar on-off switch for the headlight and gauge illumination lights. 

(Sometimes, especially when there are plastic multi-connector plugs that prevent incorrect connections, Yamaha omits the little white stripe on wires in the harness.)

When you turn headlight switch on, the yellow/white from stator powers left handlebar hi-lo beam switch and a darker blue to the little gauge illumination lights.   On low beam, the Hi-lo switch powers green to headlight and on high it powers the yellow to headlight. 


(Side note, above describes the engine powered headlight circuit.  The taillight also runs through a separate set of contacts in the headlight on-off switch that connect the brown (battery power) to taillight.)
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
Last edit: 16 Sep 2023 06:13 by MarkT.
16 Sep 2023 06:13 #2

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Replied by jez on topic D T 175 A .head light ?

Hi and thanks for your fast reply.i thought that's how it should work.i have no voltage at yellow/white in the multi connector from magneto so I'll have to trace back to behind the flywheel .cheers
16 Sep 2023 07:02 #3

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Replied by MarkT on topic D T 175 A .head light ?

Hope you can trace it down without too much trouble!  Good luck!
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
16 Sep 2023 07:39 #4

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Replied by jez on topic D T 175 A .head light ?

So the 3 coils in the magneto must supply power for ignition and lighting etc .do we know which one does what ? and is there any way to test them using a meter ?
20 Sep 2023 04:44 #5

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Replied by RT325 on topic D T 175 A .head light ?

The coil with finer windings is the one supplying power for spark.
Here's the nearest relevant manual i could find but not easy to follow for me at 1am in the morning haha.
Scroll down to page 125 & not sure if its my computer but had to crank it up to 510% to read it.
Resistance are there if you can follow it. If you see DT125 which i think it covered, then dodge that as without looking i'd guess it's the 12 volt electric start motor.
Best tell us what problem you have & see if we can help. Then again, i'm right confused looking at all that.
Not easy when they combine manuals, but looks like lighting coils are very low resistance like less than 1ohm 0.??of an ohm.
I couldn't see a resistance for the ignition source but might be around 1 to 1.2ohms wildly guessing seeing its got finer windings.
Hope someone has a better manual.
yamaha-enduros.com/index.php/service-man...a-b-c-service-manual
Last edit: 20 Sep 2023 06:16 by RT325.
20 Sep 2023 05:52 #6

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Replied by MarkT on topic D T 175 A .head light ?

The charts in the front of the manual have some specs too.

I'm not sure they show the headlight lighting coil (yellow).  I will check this evening and see if I can find it.   

 
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
20 Sep 2023 06:40 #7

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Replied by jez on topic D T 175 A .head light ?

Thanks for your help guys.i have continuity from the yellow wire at the light switch down to the lighting coil so wiring loom seems ok .the coils look intact ,should I be looking for anything specific.how would you test a coil ? Thanks again ...
23 Sep 2023 05:32 #8

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Replied by RT325 on topic D T 175 A .head light ?

Just unhook the mag loom but leave black connected for spark then give it a rev with a cheapy bulb straight into the yellow from the mag loom & see if it blows it straight away. Or AC voltage test.

Ok sounds like you've been running it sorry--but doing as above will have the other charging wires disconnected incase something is dragging it down on the charging side & robbing voltage from the yellow.
I'm likely talking rubbish & not reading the story, fully but hope it helps.
Last edit: 23 Sep 2023 16:49 by RT325.
23 Sep 2023 16:44 #9

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Replied by MarkT on topic D T 175 A .head light ?

I could not find the specs in the US manual..  RT325 posting nudged me and I dug out my Australian Cycleserv manual which shows the DT175a stator specs as follows:

Headlight - yellow wire 0.48 ohms +/- 10% @ 20 deg C (68 deg F)

Battery charge:
Green/red wire - 0.78 ohms +/- 10% @ 20 deg C (68 deg F)
Green wire 0.48 ohms +/- 10% @ 20 deg C (68 deg F)

Ignition Source coil:
2.5 ohms +/- 10% @ 20 deg C (68 deg F)
 
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
The following user(s) Liked this Post: RT325, Gr8uncleal
23 Sep 2023 17:09 #10

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