Technical Hiding relays in headlight bucket

If you think it's a great idea, go for it and you can show us the result. Many have given pros and cons, but it's your truck.

 

I have one relay for both high beams and one relay for both low beams. The dimmer switch determines which relay gets activated.

 

yes first off thanks to all who have replied. I am considering my options and will post the results when I get it wired up. I have not got the relays yet as there are differences in the mounting methods I will buy the style that works best for the mounting I need.
I did pull the wires into the headlight bucket tonight. I have the 4 light wires and a power supply in and a power out for the thermo fan and a ground if I need it. That fills the stem to the headlight bucket but still has some room so they can move a bit.
My original concern was heat from the H4 light
I still might put them on the inner fender or the firewall.

 

@ActionYobbo ,
I'm not understanding how many relays you are going to use?
Two for each headlight? One high beam, one low beam.

 

Yes 3 in the right (high, low and fan)and 2 in the left (high and low)

 

Go to American Autowire website... Pull up part number 500403. They have a description and a diagram. usually, the alternator/generator, voltage regulator, or horn relay are closer to the headlights on a vehicle than the dashboard. They are on my vehicles... That is where they were installed from the factory. You would use the original wiring from the dimmer switch to the headlights as control wiring for the relays. The voltage coming from your charging source 12v-14v (whatever your alternator/generator is putting out) would supply the power to the headlights. Thanks.

 

You don't need separate relays for each headlight for redundancy because high/low are different circuits and already give you redundancy. Having double the relays for your headlights gives you no useful benefit.

You also run the potential of overheating the relays since you have a small pocket of stagnant air around them.

 

I don’t see how relay location can change the voltage drop. Unless the wire size is different on one side of the relay. The current is the same on both sides of the relay.

 

Mine are wired like OEM did them for years , fused power to switch , switch to dommer , dimmer to lights , no discernable voltage drop , no troubles for 23 years ..

 

Current and voltage are two different things... You can have 12v-13v at the battery, but if you do not have the Amps (current) you will not crank your starter. That is the simplest way I can explain it.
Again... Go to American Autowire website, look up part number 500403, (or any automotive wiring company. I just know this part number off the top of my head) it is pretty much self explanatory.

 

That electric fan is going to pull more amps than both headlights operating in both high AND low modes at the same time (if that was possible). Point is, one relay is fine for the fan, therefore, one relay for the high beams and one for the low side is more than adequate to power both headlights. Even a quad headlight setup wouldn't require another relay typically.

I wouldn't put the relays in the buckets for those points previously made, there's no benefit to come from it other than the headache of package and future access. Put them near the fuse panel or the battery so you can access them, then wire the leads to the headlights using sufficiently-sized wire.

The only function the relays provide, as others have mentioned, is to take the load off the switch(es) and apply it directly to the headlights. In a perfect world, if the switch(es) are rated to handle the load and the wire size is sufficient, neither design (relay vs switch only) would provide brighter headlights, BUT taking the load out of the switches increases their life and makes for a safer install.

One thing to consider on you headlight bucket-mounted relay setup is all that wire connected to 12V BATT constant running back and forth. It would be much safer to mount the relays near the battery, effectively shortening the run of said constant-power wire protected by a breaker or fuse. All the wires between the switch, dimmer, and relays are carrying a much lower load as they're only required to switch the relay(s) on and off. Their size can be reduced, saving money and packaging issues as well, and you don't have all that constant hot wire running under the dash, etc. Food for thought...

One more thing, I didn't see anyone mention good GROUNDS! While you're pulling all that wire, do yourself a favor and run a ground wire from the headlights to the battery or at least a terminal that eventually leads back to the battery (bellhousing bolt, starter, etc).

 

If putting relays closer to the headlights prevents voltage drop then you're fixing a problem elsewhere that could have been fixed easier with new wiring and connections.
I still don't see why anyone would add relays to fix a 4-5 volt voltage drop? It's simply adding unnecessary components instead of fixing the real issue. I've wired dozens of cars with new wiring systems, and never used a relay yet, and never had headlamp problems or voltage drop. 4-5 volts is about a 40% loss and that would take major issues in the wiring to cause it, and it should be addressed, not fixed with relays.

 

Grounds are indeed important. But in a case as this, don't get too focused on the battery, the power to the lights really comes from the generator/alternator so that's where it needs to return. The battery is only the source when the engine is off, and most people don't use the headlights much without the engine running.

The battery and engine/generator/alternator and a bunch of other things SHOULD have soo good ground connections between them so it doesn't really matter which one you choose for the lights. Just something to keep in mind.

 

True, but I have yet to be told to attach anything directly to the alternator as opposed to the battery. I don't like relying on sheetmetal or even the frame to provide a good ground as there are too many variables and I don't like hunting down things like bad grounds.

 

I am not doing it for redundancy but to not clutter up the firewall. Stagnant air or a hot engine bay. Engine bay is hot all the time but the light bucket is only hot when the lights have been on for a while.
See the relays way at the back. That’s 5 inches behind the light

 

I mostly mess with OT vehicles on two wheels, in general they run ground wires straight to everything that needs to be connected to ground. Often one common ground wire through the harness, at the front and rear end it i connected to a bunch of wires that fans out to all electrical devices. The frame etc. is still grounded, but in general not used to conduct electricity. The starter gets a heavy ground straight from the battery.

Older bikes often used the frame as ground. Older bikes often has problems because of that. It's always fun when the lights are dim when not using the clutch, and bright when holding the clutch in - caused by poor connection engine-frame, and the clutch wire acts as conductor instead.

So yeah, in general I really like a proper ground wire to everything. Doesn't matter where it connects to, as long as it does it well.

 

I take the same approach when wiring a car and that was what I was trying to say regarding grounds. Think of the ground circuit as just that, connect everything to it and back to the battery. Don't rely on components (engine, frame, body, etc) to make the ground, link them all together and prevent a possible headache.

 

Lights and relays both produce heat. Sealed up in a box like that, I believe you'll see failures. The next day. When the sun is up.

-rick

 

A metal container. Placed out in the wind, providing lots of cooling when driving down the road.
Modern cars use smaller headlights made out of plastic and have little trouble handling the heat, as long as people don't shove higher power lamps in them. I wouldn't worry at all.

 

After all, that's why transmission cases are steel. Nope.

 

Airgaps between heat sources and sheetmetal makes for wonderful heat insulation. If he does see heat related failures, maybe some thermal paste between the unit and the bucket could help the wind shed some.

-rick