Technical Q and A for classic motorcycle maintenance and repair.
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 have recently obtained a 1970 BSA A65T Thunderbolt with a 12-volt positive ground system. I would like to keep a trickle charger on it if possible. No fancy lithium batteries here, just a plain old sealed unit. The gentleman who owned it previously had a pigtail connected to the battery for a trickle charger. He explained that the positive connection on the charger went to the grounded, positive side of the battery, while the negative side went to the, well, negative side of the battery, which is not grounded. When I connect my Battery Tender to it, the indicator light says that the charger is incorrectly connected and so it won’t charge. How can I correct this situation? If it matters, I have a Boyer ignition system. — Doug Stobbs/via email
A: Check to make sure you really have positive from the charger going to positive at the battery. I suspect it’s not. Most charger pigtails have a fuse in the positive/hot line as most vehicles are negative ground. This will confirm which is the positive line. Even though your BSA is positive ground, the fused or positive lead from the charger should still go to the positive side of the battery. In other words, ignore the fact you have a positive ground system. My unsolicited advice is to not leave the tender connected all the time, just connect it as needed, say once a week or month, and remove it once it shows the battery is fully charged.