Two gets a Headlight Relay Harness

Say what? Why?

A headlight relay harness. Even current vehicles come from the factory with poorly designed headlight wiring. The power is routed from the alternator/battery up behind the dash, through fuses and switches and THEN back up front to the headlights.

What is wrong with that?

Low voltage DC electricity (ie: 12volts) is very susceptible to voltage loss. Each connector, switch and foot of wire reduces the voltage at the end. (Remember the manufacturers accountants have their shot at the designs before the car was built. Do you think they put in BETTER switches and other parts than they had to?) We are also talking about a 33 year old motorhome... how good do you think those 70's connectors are today?

The voltage at the sealed beam headlights (also being replaced... the next project I will post) is only about 10.5 to 11.5 volts. (The charging system should be running over 13 volt to charge the battery(s).) This doesn't even let the sealed beams put out what little light they are capable of. While the best harness would be custom built for the exact application, from quality parts, I bought a pre-made harness. It was to short for the motorhome so I extended it. I also added a ground return wire (10 gauge) and two other auxiliary wires (fog and city lights).


It is ten feet from the far headlight plug (driver's side) to the ground wire, another 1.5 to the relays and a couple of feet to the passenger side headlight plug and control pick-up.



Relays, control pick-up and passenger side headlight plug.


Driver's side


Installed. Passenger side.


Installed. Power CB and ground points. Power comes from chassis side of the isolator. I could boost the voltage about 1/2 volt if I tapped from the center post of the alternator... but the headlights would go out if the engine stopped.


Installed. I followed the stock wiring harness across the coach.

Installed driver's side. (With the E-Code headlights.) Overall, much brighter. If something happens to the relays, the old harness and plugs are still there... just taped off.

Number 2 coach -- this project was about $100.