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Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.


Triumph T150V Positively Grounded

Motorcycle Classics tech expert Keith Fellenstein

Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Q: I just read your Triumph Bonneville wiring advice in the March/April 2017 issue regarding a 1979 Bonneville ignition problem where you mentioned “ground the negative lead of the VOM to frame ground.” I have a 1973 Triumph T150V which is positive ground, and I believe all earlier Triumphs were positive ground as well. I do a fair amount of wrenching on old bikes, and it might be helpful for me to know: At what point in time did Triumph switch to the more conventional negative ground? Thanks for the great column. I read Motorcycle Classics from cover to cover, and your column is like the dessert following a fine dinner! — Dave Dawes/via email

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A: Looking through the workshop manuals I see the change happening with the 1979 models. They got a new alternator that year also, the RM24, and electronic ignition, the Lucas Rita. It’s not uncommon to find older Triumphs that have been converted to negative ground. It’s not difficult for a bike running points, and it makes it easier these days if you want to use modern LED lighting. Thanks for the kind words. I enjoy writing this column.