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Wiring Harnesses and Adapters

Why should you use a Dapper Lighting Relay Harness?

In order for you to provide maximum power to your headlamps, it is recommended to have the shortest possible distance between the power source and the bulbs. Our headlight harness draws power directly from the battery, through a relay, to the headlamps. The harnesses are also fused to increase the protection in your electrical system.

Many classic car owners deal with “Voltage drop” in their electrical systems. This means that while there maybe be 13+ Volts at the alternator or battery terminal, the number drops when measured at the headlamp plug. Voltage drops can be caused by a number of things, such as corroded connectors, weak ground, etc.

The factory harnesses also were excessively long and undersized, often running power into the dash, through the headlight switch, and then back out to the headlamps. This distance creates an increase in resistance while also increasing the odds for a bad or corroded connection.

Voltage drop can severely impair headlamp output. The relationship between voltage drop and light output is not linear, it’s exponential. For example, when voltage drops to 90 percent, bulb output drops to just 67 percent of what it should be. Let’s compare what the lumen output would be in that situation:

Most cars should ideally provide 13.5V to the headlamps, at that voltage an ideal halogen headlamp will produce roughly 1200 Lumens:

13.5V : 1200 Lumens

with a 7.4% voltage drop, you would now have 12.5V at the headlamp, however, the lumens will drop over 3 times the amount, so at:

12.5V : 923 Lumens

That  7.4% voltage drop now works out to be over a 23% drop in Lumens from 1200 to 923. The graph below shows lumens at different voltages:



Good wiring provides the power to the headlamp. This is especially important for HIDs as the ballast have a minimum voltage requirement and prefer consistent power, but as you can see, halogen output can be significantly improved as well.

Have more questions? We'd be happy to help. Either send an email to or call us at 

(833) DAPPER-1 / (833) 327-7371

Interested in purchasing a harness? Click HERE to check out our relay harness.