Simplest and easiest way to relay headlights

[gabegt90]

for wiring and spaded connectors I took a hole harness from 89 vic and just hooked them up to the relays

[Yorkshire]

All you really need is two relays (autoparts stores have them) eight female spade connectors (in case the relays do not come with a harness) couple heat shrinkable butt connectors (to connect the wires from headlight switch output to relay, then relay output to headlights and a ring teminal to get power from starter solenoid or battery and various lengths and gauges of wire and a fuse holder. Tell you what...I finished up the gauge pod and I would send you the two relays and the relay holder and the inline fuse holder with fuse I used with my first relay install free of charge with the gauge pod.

What size fuse should I use?

[jaywish]

(4) 55 watt bulbs for highs = 220 watts. 220/12volts =18.33amps so I would probably go 25 amp fuse though others may think a 20 is fine. If you use 50watt highs then I would start with a 20amp fuse.

You can use two fuses, one before the low relay and one before the high relay. fuse the low beam circuit with a 15 and the high with a 20 or 25.


Anybody else?

I have not gotten around to doing this myself and probably should one of these days. I believe that explains why I have not burned out any of those Sylvania Ultras yet.

[sly]

I'm still running one Xtravision that came on the car when I got it. The high beams are original. I've got the relay mod now for 3 years and no issues. 30 amp fuse and 25 amp thermal auto-reset circuit breaker.

[LithiumCobalt]

Are there any harnesses already out there or that can be constructed so that I am not hacking up my vehicle's original wiring? Would be nice for a plug and play alternative.

[kodiak]

Here is how I did it. One change I made was outside hi are on one relay as are inside hi.



Some thoughts on upgrading your headlights. Why upgrade? OEM wiring and headlight switches are engineered to balance low cost with minimum standards of safety and reliability. The moment you want to give yourself better lighting you have to take into consideration the capabilities of the current OEM wiring and headlight switch. Before you upgrade your lighting you should have knowledge of electrical properties and nomenclature. Basic electricity lessons can be found all over the internet and I recommend you learn before you upgrade. Knowing how is only half the battle. It is in your best interest to know why.

Before you begin you'll want to source all your wiring and components. Look for high quality in the components you buy. It will save you time and frustration in the long run. Things to look out for are relay amperage rating, wire size and capacity, terminal construction and durability. Simple things like soldering, shrink wrapping and wire loom wiring and terminal ends not only give a neat appearance but also add strength to the connections. Ground wires should *be the same size or larger than your power wires.

As you select the components, pay special attention to the wire gauge. Looking at Ohm's law, we see that current (amps) = watts / electromotive force (volts). In my case I have 400 total watts of high beams, so 400w / 12 volts = 33.33 amps. That's more than enough to damage and burn you and/or your vehicle!

From www.powerstream.com:

As you might guess, the rated ampacities are just a rule of thumb. In careful engineering the voltage drop, insulation temperature limit, thickness, thermal conductivity, and air convection and temperature should all be taken into account...

...The Maximum Amps for Chassis Wiring is also a conservative rating, but is meant for wiring in air, and not in a bundle. For short lengths of wire, such as is used in battery packs you should trade off the resistance and load with size, weight, and flexibility.

From the Handbook of Electronic Tables and Formulas:

18 ga 16 amps
16 ga 22 amps
14 ga 32 amps
12 ga 41 amps
10 ga 55 amps

As quoted, the values are for open air wiring. Loomed wire in a hot engine compartment needs to be considered when choosing wire and relay carrying capacities. For my upgrade I chose 40 amp 5 pin relays (two 87 outputs), 10 ga wire and ceramic H4 plugs. I also split the high beams into two circuits. My two high beam circuits are carrying about 17 amps and my low beam circuit is carrying about 18 amps. All circuits are protected using 25 amp ATO fuses. I gave myself a good margin to protect against overheating and wire temperatures that will occur in the summer time.







About me:
I am a journeyman HVAC/R tech with over 20 years experience. I troubleshoot, service and repair AC and DC electrical components and various types of refrigerant systems in commercial, supermarket and industrial applications. I enjoy working on virtually anything mechanical and electrical.

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