Positive or Negative Ground for 1973 Triumph TR7RV?

A reader is trying to determine whether his 1973 Triumph TR7RV is positive or negative ground.

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by Keith Fellenstein
Ready to take your classic queries: Tech Editor Keith Fellenstein

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Positive or negative?

Q: How would I determine if my 1973 Triumph TR7RV is positive or negative ground? I assumed that it was positive ground, but I hooked it up that way and it blew the 30-amp inline fuse on the negative cable. I do not know a lot about these British bikes. Thanks.

G. Manning/via email

A: First off, use a 15-amp fuse, as the ratings are different between British and U.S. fuses and a 30-amp British fuse as called for in the rider manual is a 15-amp American fuse. Next, the fused negative cable goes on the negative post, the positive post (red wire usually) goes directly to ground. If it still blows fuses after these changes, there is something else wrong with it. All this advice assumes it’s got the standard plate rectifier and Zener diode voltage regulator. If it has an aftermarket regulator/rectifier combo it may be a little more difficult to troubleshoot. Let me know if this fixes the problem.

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