Nick’s hazard warning light add-on

For some time, I’ve been tinkering with LED lighting on my Mk3 Commando.  Having read some articles that made LED conversions  more complicated than necessary,  I though I’d have a go at a simpler solution.  My first article in Roadholder (No. 344 page 37) was on LED indicators, using off the shelf components.

When converting to LED indicator bulbs, the standard filament turn indicator pilot light allows sufficient leakage current to cause both the selected turn indicators and the opposite string of indicator lights to illuminate.  To mitigate this, suppliers of LED conversions offer a current snubber circuit that comprises two diodes.  The snubber blocks the current leakage path through the indicator pilot light.

In this article, I propose an extension of the current snubber circuit that uses two additional diodes and a single pole, single throw switch to allow all the LED turn indicators to flash simultaneously and thereby provide a hazard warning feature.

Figure 1 shows both the original two diode snubber and the two diode extension.  Usually, discrete diodes are used for the snubber.  However, in the proposed configuration, a more compact bridge rectifier can be used.  This is a single component, comprising four diodes, that simplifies the installation.

The handlebar switch for the hazard circuit contains a LED for illumination.  In this instance, I’ve configured this to illuminate when the indicators flash.  It would also be feasible to set this up so that the switch illuminates when the headlamp’s pilot light is on.

Figure 1 – basic LED indicator set-up with additional hazard warning light function

The handlebar switch for the hazard circuit contains a LED for illumination.  In this instance, I’ve configured this to illuminate when the indicators flash.  It would also be feasible to set this up so that the switch illuminates when the headlamp’s pilot light is on. These items are illustrated in Figure 2.

Figure 2 – Handle bar switch, bridge rectifier and wired-up rectifier.

Figure 3 depicts the system in use with all indicators flashing when the hazard switch is on. Although the system functions well, I may reposition or replace the switch with a larger one to make it easier to operate.

Figure 3 – Basic LED indicator set-up with additional hazard warning light function

© Nick Harwood – 10th April 2021