These do not drop forward voltage to 9 volts. They have a reverse breakover voltage of close to 9 volts. 500mW DO-35 Zener Diode used in many Honda motorcycle ignition systems. Without it there will be no spark. Most aftermarket ignition modules do not have this diode built in so you will have to add it. You can either solder it onto the empty contacts of the replacement ignition module or solder it into the wire, shown as the pink wire in the image above that runs to the ecu. It is directional so it will need to be installed in the proper direction to work, but no damage should be done if installed backwards, it will just not work. This diode also acts as an anti theft deterrent. I do not have a complete listing of what models need this diode, only a partial. If you have additional models to add, please let me know. 7/13/2023 - just fyi I have had a few people (2 so far) that think these are used to drop forward voltage to achieve the intended goal. While they do drop forward voltage a little (approx 1.6 volts), that is not there intended purpose in this application. They are used here to prevent current flow up until the breakover point (approx 9 volts) where then reverse current is allowed to flow. I found a nice link that explains this more from the university of Oklahoma. See "zener diode section" . You will have to add an "l" to the end of the link. https://www.nhn.ou.edu/~bumm/ELAB/Lect_Notes/diodes_lecture_v1_2_2.htm Here's some AI info I found useful in explaining how they work. ? Understanding the Zener Diode Reverse Breakdown Voltage A Zener diode is a special type of diode designed to reliably operate in reverse breakdown?something regular diodes try to avoid. Let?s walk through how it works and why that breakdown point is actually its claim to fame. ?? Reverse Breakdown Voltage Defined - The reverse breakdown voltage (also called the Zener voltage) is the precise voltage at which the diode begins to conduct in reverse bias. - Unlike regular diodes that might get damaged at this point, Zener diodes are engineered to handle it safely. ? How a Zener Diode Uses It When reverse biased (negative voltage applied to the anode and positive to the cathode): - Below Breakdown Voltage - The Zener diode acts like a regular reverse-biased diode: it blocks current flow. - At Breakdown Voltage (Vz) - The diode begins conducting in reverse. - It maintains a steady voltage (Vz) across itself, regardless of increases in current. - This voltage regulation is incredibly useful! - Why It Works - Breakdown is due to quantum tunneling (Zener effect) at low voltages and avalanche multiplication at higher voltages. - The diode's internal structure controls which effect dominates and what breakdown voltage it exhibits. ? Applications Zener diodes shine when you need: - Voltage regulation (e.g., keeping 5V stable across a load) - Reference voltages in circuits - Overvoltage protection I hope this helps. Thanks for looking 4/23/2025 - USPS services at the Atlanta Regional Processing and Distribution Center in Palmetto, GA have been experiencing significant delays for the past month. I am told these issues stem from the consolidation of several distribution centers into the new Palmetto facility. Some shipments seem to go right through while others will sit for a week or more. On standard shipments I can not issue a missing mail request until 15 days have passed, for Priority it is 7 days. My hands are tied, I have added UPS services as an option.