Cables from the generator to the voltage regulator

I’ve already ridden well over 15,000 trouble-free kilometers on the DB3. But in August 2023, I break down on the last stage of my Alpine tour, which leads from Ponte di Legno on the southern side of the Gavia Pass back to the Allgäu.

Around 300 kilometers and eight breathtaking Alpine passes are behind me, with just over 100 km left to the Allgäu. Past Davos, on the way down into the Rhine Valley, I notice that the indicator lights on the dashboard are getting dimmer and dimmer. Not a good sign! A short time later, the bike dies because the remaining voltage is no longer sufficient for the ignition.

Since I replaced the two lead-acid batteries with lithium-ion batteries only two years ago, the voltage drop must be caused by either the regulator or the generator. In the best-case scenario, a connector has come loose or a cable has been damaged due to securing my luggage on the seat.

A stroke of luck in my misfortune: I roll to a stop just a few meters in front of a workshop. The owner immediately takes care of me, lets me push my DB3 into the hall, and comes to help with a portable jump-start power pack. As soon as the clamps are connected, the bike starts right up. Then he grabs a multimeter and measures the voltage at the battery, which doesn’t change even when revving the engine – the battery is not charging. I borrow a pair of side cutters, remove some cable ties to check the wiring under the subframe for possible damage. No luck there either, so the most likely culprit is the voltage regulator.

At this point, I’ll cut the story short and get straight to the cause of the breakdown. After installing a new voltage regulator doesn’t fix the problem, I measure the AC voltage between the generator output terminals – nothing! My last attempt before removing the alternator is to check the cables, which can only be accessed after removing the tank – quite a bit of work on the DB3. Instruments off, handlebars off, fuel lines, etc. And sure enough, the cause of the breakdown is two burnt cables running from the generator to the voltage regulator, routed on the inside of the frame just a few centimeters from the rear cylinder and exhaust header. Most likely, both age and the strain of the eight passes finally took their toll on the material.

So here’s my tip: check the cable routing on your DB3. I extended the cables and secured them to the cross brace that holds the shock absorber to the frame. This significantly increases the distance from the cylinder head and, most importantly, from the exhaust header.