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DT 250a 12v Conversion

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DT 250a 12v Conversion was created by ziggybomb

I've bought a 6v to 12v conversion kit last week from Rex speed shop. And have started to fit, all quite easy until I removed stator there is a brown wire that connects ignition coil to the lighting coil. See photos attached. According to the workshop manual the coils are not connected in any way. Does anyone know what to do with this brown wire?
17 Oct 2021 05:36 #1

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Replied by MarkT on topic DT 250a 12v Conversion

All I know for sure is that many models had the coils connected.  I have a pretty good guess, but this is really a question for Rex's.  Good luck.

Maybe someone here has had the same situation with that kit and will comment.
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
17 Oct 2021 06:24 #2

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Replied by rhineman on topic DT 250a 12v Conversion

How did the conversion work out? I am purchasing the same package from Rex's for my 175E. 
17 Oct 2021 11:17 #3

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Replied by ziggybomb on topic DT 250a 12v Conversion

I cannot finish the till i know what to do with the brown wire that is connected to both coils, nothing about it in the rex instructions.
17 Oct 2021 11:40 #4

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Replied by MarkT on topic DT 250a 12v Conversion

Wondering what Rex will tell you.  I searched the forum and found several questions and issues but not that exact one. 

Anyway, you mentioned that wire wasn't mentioned in the manual...  just FYI, that wire is clearly shown in the parts diagram so don't let anyone say it's not original or something...

 


Several models connected the ignition source coil to the lighting coil.  Magnetos seem to run on black magic...  look super simple but the engineering is very complex...  I've spoken to a couple of very smart Electrical Engineers who told me that designing points magnetos like Yamaha used is a very specialized field and probably close to a lost art.  More modern systems are just basically permanent magnet alternators that power electronic circuitry.  Much less complex in terms of engineering.

Anyway, presumably the connection to the lighting coil increases available spark energy.  Will it have spark without that connection?  Almost certainly as long as the wire is grounded well. 

Hopefully Rex's will give you a solid answer on what to do.
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
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17 Oct 2021 18:12 #5

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Replied by RT325 on topic DT 250a 12v Conversion

I wonder if it is a bit like a cdi having a high speed coil to boost spark at revs. All i know is mine is earthed separately but don't have a lighting coil Maybe all these years i've been missing out on top end performance. I know on my 490 with a crook high speed coil that piggy backed to the main source, i removed it & ran a simple box of a yamaha old scooter & wasn't ever an issue. But now i wonder!! what i missed out on. Always new 'old' things to learn.
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18 Oct 2021 03:32 #6

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Replied by MarkT on topic DT 250a 12v Conversion

Spark only has to be "good enough"...  power is really only lost if mixture doesn't ignite at all. 
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
18 Oct 2021 07:46 #7

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Replied by ziggybomb on topic DT 250a 12v Conversion

Thanks for your replies, but still non the wiser ,sent the question to rex speed shop tech help via email on Sunday no reply yet so still no progress,
18 Oct 2021 09:25 #8

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Replied by MrBernzo on topic DT 250a 12v Conversion

How did you go with this issue?
I did the same conversion a few years ago and had the same problem.
From memory Rexs advised me to simply cut the brown wire.
I can take my stator cover off tomorrow and take some photos.
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27 Oct 2021 05:11 #9

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Replied by ziggybomb on topic DT 250a 12v Conversion

Yes finally sorted the problem the brown wire is an earth from the ignition coil, so leave as long as possible cut the wire strip and solder a round terminal to the wire and place under screw that holds ignition coil. (Bottom) screw. This should solve the issue.
27 Oct 2021 09:10 #10

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