H4 Heavy Duty Wiring Upgrade

[tomsoffroad76]

We get a lot of questions this time of year regarding lighting with the days getting shorter and Bronco's find themselves in the dark, its important to have a clear view of the road ahead. Let's shed some light!

H4 Headlight Upgrade Guide

We put together the parts to easily plug and play a heavy duty wiring harness enabling the ability to run hi and lo beam at the same time. Great time of the year to upgrade if you haven't.

What's been your experience with your Brocno's lighting upgrades?

 

[Steve83]

When the factory wiring is properly maintained & repaired, add-on systems are not necessary. They might be easier to install than finding & fixing the real problem, but they're MUCH more expensive, and are subject to the exact same problems over time that caused them to be installed. So they really don't "fix" anything; they're just bandaids. Ford's original design for the headlight circuit has no defects to be corrected - it's just the old wires, switches, & connectors that probably need some attention.

And running both filaments is very dangerous to the bulbs & housing, unless the headlights have been replaced such that the high & low lights are inside separate reflectors. A single reflector is not designed to dissipate that much heat.

 

[pbwcr]

Agree with Steve84.
And if you use LED bulbs then functional stock wiring will be more than adequate. The LED bulbs have way more lumens that any halogen bulbs.

 

[bigmuddy]

Your really saying that it's not better to trigger the headlights with relays instead of just running everything thru the switch> I think most will disagree with you and Steve.

LEDs are fine, but for those of us that still drive in the winter they don't provide any heat to keep them clear of snow and ice.

 

[DirtDonk]

And not everyone wants, or can, spend the kind of money that good LED's cost. Or can justify the crappy performance of some of the LED H4-retrofit bulbs.

I don’t disagree completely on principle, but I disagree in dismissing the product, based on how this harness relates to the real world.
The original wiring, when in perfect original condition, was perfectly adequate for 45 W bulbs. The fact that it didn’t melt when you left the high beams on was all the factories cared about. High-beam performance was not all that stellar.
Back in the 60s, the lamp output wasn’t all that great to begin with. You would’ve never noticed a small voltage drop because the lights weren’t that good. But as the rigs got older, the loss in light was often very noticeable.
Install a modest set of 55/60 H4’s however, and the wiring just wasn’t up to the task. Every set of H4’s I ever installed in an old vehicle failed the headlight switch prematurely. Every one… And I think we’ve seen over the years quite a few reports of the same thing here on other Broncos.

Put 50 years on that wiring however, and it’s just stupid not to upgrade your wiring to a relay system. Not taking advantage of modern solutions doesn’t make any sense. Especially when the cost is minimal.
Sure, the original equipment manufacturers ran the wires through the switch and out to the headlights. But they haven’t done that in regular production for 40 years. There were some holdouts, but most went over to relays long ago.
Toyota was running relays almost 50 years ago. Most of the American manufacturers have been doing it for most of the last 35 years at least.
Maybe there are some that still don’t use headlight relays, but I don’t know of them.
And I don’t know why they would.
The only advantage to not using relays is that you have fewer things to fail. That’s not worth the potential loss in performance. Or the possibility of losing all lighting from an overloaded headlight switch.
Even with LEDs needing less current to do their job, they still benefit from a steady source of full system voltage. That 50-year-old wiring going through the old circuitous route, does not provide that. Not reliably anyway.

If you do a complete harness replacement, chances are that the new wires and switches can handle higher current H4’s very well. But since many of us choose to forgo the standard 55/60 W output bulbs and go to 55/100s for those killer bright highbeams, I still say relays are a better choice.
Why put more burden on the main headlight switch for a longer time than it was designed to handle.
My factory original 71 headlight switch tripped it breaker about a week after I installed the H4's and the second time I turned on the high-beams. And those were the standard 60 W high beams.
It was about 15 years old at the time, so not brand new. But adding the relays gave it a new lease on life.
Work perfectly fine for the main lights until I had to replace it several years later because the instrument cluster rheostat started giving me trouble.

So from my own experience, and for many here on the forums, and for the OEM lessons, I’m in favor of relay upgrades to get the most out of your system.
No matter what light style you choose.

 

[spap]

I have the wild horses wiring upgrade, in my H4 lights I run 55w/100w halogen bulbs. The lights get hot.
I have had no problems with the wiring upgrade , pretty simple and peace of mind

 

[Steve83]

Your really saying that it's not better to trigger the headlights with relays...

Correct - there is no advantage to adding a relay. If there were, then you could trigger the relay with another relay; and trigger that other relay with a 3rd relay... The switch was designed & built correctly to handle the current that the stock headlights needed. If you use modern lights that need less current, then the stock switch is already overkill.

I think most will disagree with you and Steve.

It won't be the first time, or the last!

...for those of us that still drive in the winter they don't provide any heat to keep them clear of snow and ice.

What do those of you do with your modern vehicles that were built with big plastic headlights; either with a lot of distance between the lens & bulb, or with low-temperature (LED/HID) bulbs?

 

[Yeller]

Modern vehicles with LED bulbs use a heated lens for the headlights. At least the one I currently own does. The best aftermarket ones offer it as an option, JW Speaker does as example.

 

[Steve83]

Good to know, but it must be optional on vehicles sold a lot farther north because I've never noticed them around Memphis or St. Louis. I can't even find a Ford model with that circuit.

 

[ntsqd]

MISF regards my 55/100's as puny and hardly worth the effort. He typically uses 100/135's or something like that. Maybe they're 130/165's? Anyway, always with relays. Even with that wattage his light output doesn't quite match an HID or a LED. They don't live as long, either. These H4's would KILL the stock wiring and switches.

Something that has been either ignored or unacknowledged in this thread is voltage drop. The HL's may operate fine with the stock wiring, but the combination of the original wire gauge used, coupled with the length of the whole circuit, in combination with any corrosion or other resistance producing degradation in the circuit can easily result in an unacceptable voltage drop. Sure, the lights work, but when they are under-voltaged they tend to not last as long as they could nor do they put out the useful light that they could. Run the numbers, I use Ancor Marine's Resources page for sizing the wires in all of my wiring projects. It is a rare circuit that I size the wires for a 10% or less voltage drop. Most circuits I size for a 3% or less voltage drop. It doesn't take much to get a 10% voltage drop. This is the real argument in favor of relays. With relays the whole circuit can be significantly shorter and you can size the wiring to have very minimal voltage drop. This isn't license to wire the HL's with 4 gauge (unless you want to, but why?), but if you want the HL's to perform at their best all of this needs to be considered.

Look at the recent thread about the Koito H4's. That kit is a factory Toyota kit to upgrade the lights on FJ40's, FJ60's etc. It comes with the relay harness. It isn't just the aftermarket that does this. The factory wiring isn't up to that many amps. The Bronco wires are a larger gauge than the Toyota wires, but they're not that much larger.

I have had a reflector fail when running with both the low and the high elements lit when on high beams. It was a plastic reflector in a non OEM replacement HL assembly. In 30 years of doing this with metal reflectors I've never had a problem. I acknowledge that I'm only one data point, but my data point spans a considerably long time with at least 5 different semi-concurrently owned vehicles. If something was going to happen it would have. I'm never that lucky. BTW, I put relays in the second vehicle to get H4's because the lighting wasn't as good as it should have been. The first vehicle to get them, my avatar, was wired from the start with 10ga. when I built the whole loom.

CA has (had?) some odd laws that few seem to know about. Max illuminating* elements is limited to 6. This could have changed, it's been years since I made that deep dive into the lighting laws. Here's the thing though, if you have a dual headlight vehicle and you have it set-up so that all 4 highs and the lows come on with the highs, then you're already at the 6 elements limit and can't have any other illuminating lights working. No idea if other States have this same law. Or how they've changed the language since not all lights now have elements in them.
Also in CA driving lights can only be lit with high beams. Fog lights can only be lit with low beams. Auxiliary lights can be lit with either.
ALL of my extra highway use lights are "auxiliary".

*Marker lights etc. don't count since they're not intentionally Illuminating.

 

[Steve83]

Something that has been either ignored or unacknowledged in this thread is voltage drop.

Yes, that's the whole point of the kit, although it wasn't stated. And it's apparently "a heavy duty wiring harness", so none of the issues you mentioned apply. The only thing the factory wiring would do is power the relay(s), which don't pull enough for a voltage drop, and wouldn't behave any differently if there were a drop.

...when they are under-voltaged they tend to not last as long as they could...

Actually, they last longer when they don't get as hot.

 

[pbwcr]

The the Toyota kit is intended to replace old school traditional standard lights with tungsten bulbs and they recognize that folks are using 100 watt + halogen bulbs. which why they provided a fat wire HD harness with relay.
Now days we have the option of using LED bulbs for the obvious advantage of way higher lumens and way lower current.
What would be a good thing to do:
Leave out the relay for less com[plication for better reliability and buy some proper high/low beam LEDs.
I have LEDs in one of my rigs and WOW! what a difference compared to 100w Halogens.
And yes's the EB stock wiring is adequate for the LEDs as long as it is in good shape.

 

[Yeller]

on this subject how many of you carry a spare dimmer switch? I have had a LOT of them fail over the years. Every vehicle I own with a foot dimmer switch has a spare in the glove box, more than once I've had to stop and change it. way more failure prone than the dash switch.

 

[ntsqd]

The Toyota HL wiring that I'm most familiar with, mid 80's trucks and FJ60's, is barely able to handle the loads of a sealed beam HL. The relay kit is really necessary even with sealed beams.

Sounds like those might be like Dura-Spark II modules, the JY sourced, 20+ years old part is better than what you can buy new from anyone. Grandad used to grind the heads off the rivets on Ford type starter relays and tune-up the internals when they started misbehaving. He put them back togehter with machine screws and nuts. I've never had cause to look, I wonder if the same can be done with these switches?

 

[Yeller]

The Toyota HL wiring that I'm most familiar with, mid 80's trucks and FJ60's, is barely able to handle the loads of a sealed beam HL. The relay kit is really necessary even with sealed beams.

Sounds like those might be like Dura-Spark II modules, the JY sourced, 20+ years old part is better than what you can buy new from anyone. Grandad used to grind the heads off the rivets on Ford type starter relays and tune-up the internals when they started misbehaving. He put them back togehter with machine screws and nuts. I've never had cause to look, I wonder if the same can be done with these switches?

for the $6 they cost and the 30 seconds it takes to change enough to get back on the road, I've never messed with opening one up. I'm sure they can be cleaned and tweaked back into commission like most old school automotive switches. My theory has been, they are constantly getting a good dose of dirt being on the floor, not helping their longevity.

 

[Tobtech]

The OEM wiring in a 66-77 Bronco is NOT sufficient for many upgraded headlight systems available today. Maybe for LED headlights but there is so much imported crap that you can't even be confident that the stock wiring and switch can handle any LED upgrade (yes, LEDs can draw current too). Not to mention the reproduction switches available for both Ford and GM are garbage. With that in mind, relays make total sense. Now the unsealed relays in the photo in the article will last less than a year under the hood of a Bronco so gitcha some sealed "Hella Style" relays and it will last another 50 years.

 

[toddz69]

for the $6 they cost and the 30 seconds it takes to change enough to get back on the road, I've never messed with opening one up. I'm sure they can be cleaned and tweaked back into commission like most old school automotive switches. My theory has been, they are constantly getting a good dose of dirt being on the floor, not helping their longevity.

I was going to reply and mention that most of the dimmer switches lead a hard life with all the dirt, mud, snow, water, etc. I can remember changing one on my truck about 20 years ago.

The first headlight switch in my truck lasted 15-16 years. It failed on a long trip with several other rigs. Thankfully it was on a lonely dirt road on a night with a full moon so Dad told the other rigs to turn their lights off too so everyone could see. The second switch has lasted the last 37-38 years, with relays lightening the load on it for about the last 20 years.

Todd Z.

 

[ntsqd]

The original design of those switches was built with that environment in mind. Not that this made them impervious to it, just that it gave them a fighting chance.

 

[Steve83]

...there is so much imported crap that you can't even be confident that the...relays make total sense.

Why would you trust a relay more than a switch or headlight?

My theory has been, they are constantly getting a good dose of dirt being on the floor, not helping their longevity.

But they were engineered specifically for that environment. The original one from my '83 Bronco is still working, although it's now a bypass to the clutch pedal switch so I can start in gear.

 

[Tobtech]

Why would you trust a relay more than a switch or headlight?

But they were engineered specifically for that environment. The original one from my '83 Bronco is still working, although it's now a bypass to the clutch pedal switch so I can start in gear.

This answer could get very long but this isn't the venue to teach a class. The short answer is, relays are available in all sizes and specs and I purchase the correct ones for the application. I mean, can you run an electric fan through ANY switch? No, it would melt within 24 hours with the wrong switch. With relays I also control the gauge and length of the 12 volt feed into the relay. I make sure its sufficient and its also dedicated to that circuit. The OEM headlight switch pulls its 12V from a feed that is common with the feed to the fuse box and fed from the battery, starter or alternator and depends on the quality of that connection.