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1968 Triumph Bonneville Voltage Regulator Upgrade

Making sure your charging system is working to full capacity is important on a number of fronts. To begin with, there’s the simple issue of generating enough voltage to keep your lights bright. This is particularly important on vintage bikes, which generally have low-capacity charging systems and run low-output headlights, which tend to be dim even with full voltage. And even if your lights are off, there’s the issue of generating enough voltage for proper ignition. If you own a decades-old British twin, chances are good you’ve already ditched the stock ignition points for electronic ignition, a highly recommended upgrade to ensure steady, reliable firing of the spark plugs. However, some electronic ignitions are very sensitive to voltage supply, dropping completely out of circuit if the voltage drops below a certain range. Boyer electronic ignitions, for example, will drop out below 10 volts.

On Sixties and Seventies British bikes, the original Lucas charging system can be prone to failure. By the mid-Sixties, most British motorcycles were using Lucas charging systems with Lucas’ silicone diode rectifier for AC to DC voltage conversion and a Lucas zener diode for voltage regulation. Although relatively simple components, after 40-50 years of vibration and exposure, the voltage regulator and rectifier are ripe for replacement. The original-style components are still readily available, but there are better products on the market that deliver superior performance and reliability, like the Podtronics voltage regulator/rectifier we recently installed on Tech Q&A man Keith Fellenstein’s 1968 Triumph T120R Bonneville.

Keith’s Bonneville didn’t have any particular charging issues, but with a fresh Pazon electronic ignition upgrade, and wanting also to convert to 12-volt negative ground from positive ground, Keith considered it a good move. Adding to the appeal, it’s also a relatively cheap and easy conversion. The Podtronics unit was $57 (before shipping), and while we did opt to clip off what became redundant ground lines from the old rectifier to the battery and frame, had we wanted to, we didn’t have to make any permanent changes to the original wiring. Keith’s bike already had a replacement wiring harness, so we didn’t feel bad about altering it in any way as it’s not original.

We also like this upgrade because A) it delivers superior performance over stock and B) the only way anyone will know the charging system has been changed is if they lift the seat and see the new Podtronics unit in place of the original Lucas silicone rectifier. On 1968 and up through the mid-Seventies Triumphs the Lucas regulator (the zener diode) is housed in a large, finned aluminum heat sink attached to the bottom of the lower fork yoke. You can leave it in place to preserve your bike’s original looks, as we did, or remove it. For the conversion, we isolated the wiring to the zener diode and then tucked it into the headlamp shell.

We also switched the Bonneville’s electrical system from 12-volt positive to 12-volt negative ground. The Podtronics will work either way, as will the Pazon electronic ignition. Switching from positive to negative ground is easy, requiring no permanent changes. Finally, we upgraded to an LED headlamp and taillight. The taillight was a Sylvania Zevo 2357R red LED ($24.95 at O’Reilly Auto Parts). We got our H4-style headlight shell ($44.95) and 80-watt LED bulb ($59.95) from Donelson Cycle. You’ll also need an H4 headlamp socket and pigtail ($3-$5 at O’Reilly). The lights are much brighter and with a significantly reduced amperage draw, and they’ll basically last forever.

As ever, we recommend having a good shop manual on hand for parts identification and proper torque specs.

1) Disconnect the positive lead to the battery, followed by the negative lead. The stock silicone diode rectifier is located behind the battery box. Remove the nut securing the rectifier. Remove the rectifier and disconnect the electrical leads.

2) The zener diode, which regulates charging voltage, is housed in a large heat sink located on the lower fork yoke. We left it in place to preserve our bike’s original look, but it must be taken out of circuit. Remove the ground strap from the bottom of the heat sink, then resecure the heat sink to its mount.

3) Next, reach behind the heat sink and unplug the brown/white lead running to the zener diode.

4) We left the wiring to the zener diode in place, isolating it from the system by sealing it in heat-shrink tubing.

5) Next, we routed the now isolated wires into the headlamp bucket to keep them out of the way.

6) We also converted our Triumph from positive ground to negative ground, which required swapping the blue/brown and brown/white leads to the ammeter in the headlamp housing, shown here as they were positioned originally, with the brown/white lead already disconnected.

7) Next, we mounted the new Podtronics regulator/rectifier, securing it with a single bolt to the same locating point as the original rectifier.

8) We then connected the black lead from the Podtronics to the red ground lead from the wiring loom that previously ran to the ground post on the stock rectifier, wrapping the red lead with black heat shrink tubing to color code it as negative ground after first removing the now unneeded extra red leads that ran from the rectifier to the frame and battery.

9) Next, we connected the brown/white lead (which we marked with a “+” for positive) previously disconnected from the stock rectifier to the red lead to the Podtronics unit.

10) Connect the green/white and green/yellow alternator leads that ran to the Lucas rectifier to the yellow leads to the Podtronics unit. The alternator output is AC so it doesn’t matter which alternator lead goes to which yellow lead to the Podtronics.

11) We installed a 15-amp blade-type fuse to the blue/brown power lead from the wiring loom after covering the blue/brown lead with red heat shrink tubing. The eyelet will run to the positive side of the battery.

12) Here’s the battery back in place, with the now red fused power lead running to the positive side of the battery and the formerly red but now black-sheathed ground leads running to the negative side of the battery.

13) Our Triumph was already running a Pazon electronic ignition. The Pazon will work with either negative or positive ground. With the conversion, the red and white leads had to be swapped.

14) As wired for positive ground, the red lead from the Pazon ran to the “+” side of the left ignition coil and the white lead ran to switched power. The red lead running rearward from the coil goes to ground.

15) With the conversion to negative ground, switched power connects to the “+” side of the left coil. The red lead running to ground connects to the white lead to the Pazon.

16) We replaced the stock headlamp and taillight with LED bulbs. For the headlamp, that meant getting a complete shell compatible with H4-type halogen bulbs, but fitting it with an LED bulb. The replacement headlamp is on the left, the stock to the right.

17) For the taillight we used a Sylvania Zevo 2357R red LED bulb, which directs the light to the reflector. Like the LED headlamp, it’s brighter and uses less power than the standard incandescent bulb, and should last basically forever.

18) The ammeter gauge tells the tale, the current draw with lights on dropping from 4 amps-plus (top) to less than 2 amps (above).

Published on Feb 13, 2018

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