Four-panel guide soldering a 200-ohm resistor into a wiring conn…

Brake LED Resistor
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Since there are many other systems (ABS, cruise, electronic automatic transmission...) that rely on the BOO (Brake On-Off) circuit, there can be many consequences in converting all the brake light filaments (2 in older vehicles, 3 in those with CHMSL) to LED. Adding a single ~180 Ohm 2W resistor from anywhere on the BOO circuit (511 LG) to any ground (57 Bk, 206 Wh, or several others) will keep those systems working as they should, while still giving all the benefits of LEDs (longer bulb life, lower current draw, lower temperature).

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The trailer brake controller connector is a very convenient place to add the resistor because it's easily-accessible, inside, and doesn't require additional insulation because no wires are cut or stripped. After marking the terminal locations on the plastic connector shell (pre-'94 trucks have only 4 wires), pry out the red lock, and release the 2 target terminals. Brush the corrosion off the crimps, down to shiny metal. Then use the soldering iron to heat the terminal until solder melts onto that clean area of the crimp. While it's still hot, attach one of the resistor's leads (it doesn't matter which - resistors are not polarized) to the wet solder, and let it cool. Make sure it has a mechanically-strong connection, and repeat on the other terminal. When they're cool, re-insert and lock them into their original positions in the connector shell.

The resistor will allow the truck to work properly with LEDs as brake lights, incandescent bulbs, or a mixture. No other bulb position affects these systems this way, but a few other bulbs affect other systems in other ways (alternator charge indicator, 4WABS indicator, SRS warning lamp...) and should remain incandescent. Most convenience lighting and other exterior lighting is safe to swap to LED without adding resistors.

Owner caption April 2021 · Photo 0 of 5000