Upgrade to Brighter Headlights

Now that my dash lights are looking better, and (more importantly) the weather has cooled off considerably, I decided it was time to tackle the problem of piss-poor headlamps in our Mustang.

Given how dim the old headlights (a pair of Sylvania 6014s running on what I presume was stock factory wiring) were, I have to wonder just how it is that folks manage to drive at all at night with these classic cars. In my case, after-dark driving in the Mustang was not something I wanted to do if it could be avoided. But with no A/C, and consistent 100-degree Oklahoma summer days, when else ya gonna drive the thing (and not be sweat-soaked and miserable)?

Factory Headlight Wiring Has to Go

So, if you want to boost the headlight performance of an old Mustang, the first thing to realize is that the factory headlight-wiring setup was never intended to handle much current. Aside from forty-year-old wire, which is likely not in great shape, the largest drawback is that the headlamp’s power doesn’t come directly from the battery. Rather, the circuit runs through the headlight switch itself. That, at least, is what I’ve gleaned from lots of internet reading on the topic. Makes sense to me.

Today’s newer, brighter halogen headlamps — which actually DO light up the road, rather than just throw a splash of yellow/brown haze over it — work great, but they need significantly more power than did the lamps of thirty or forty years ago.

Sure, you could plug a pair of 55-watt halogens into the factory sockets, and change nothing else. But flickering lamps usually follow — as does smoke from behind the dash, if you really push things. (That 1960s-era headlamp switch can handle only so much abuse, ya know.)

Taking a Load Off (the Factory Wires)

The solution here is to install a new harness in place of some of the aged, brittle factory harness that’s already there. In this new harness — which gets power straight from the battery — are a couple of relays. The new harness connects to both of the headlamps, as well as to one of the old harness’ light sockets. Thus, when you turn on the headlights, the headlamp switch’s signal activates the relays, which in turn send current directly from the battery to the headlamps. This accomplishes the goal of getting full battery power to the headlamps via new, heavier-gauge wire. It relegates the old harness to use only as a small-current pathway whose only task is to activate the relays.

To my knowledge, there are a couple of makers of such a harness. The first is Reenmachine:

Reenmachine: Halogen Conversion Kit

And, of course, Scott Drake:

Scott Drake: Headlamp Relay Harness

The Reenmachine kit comes with two Hella halogen lamps, and currently runs $225. The Scott Drake harness doesn’t come with lamps, and can be had for $120 or so at a host of retailers.

The Theory Behind a Relayed Setup

For those of you with the motivation for building your own relays-and-harness setup (or who need schematics to do a little troubleshooting), here are a few helpful links:

Daniel Stern Lighting: Headlamp Circuit Upgrade

Mustang Grabber Registry: Install Headlight Relays

And a decent overview of the classic Mustang electrical system:

Mustang Monthly: Troubleshooting Your Electrical System

The New Harness …

I purchased the Scott Drake relay-installed harness from CJ Pony (CJP part number WHLR; Scott Drake part number C5ZZ-14290-RH). This harness, as described, is compatible with 1965 to 1973 Mustangs; it set me back a litle over a hundred bucks. (I’ve read that the same stuff could be bought from Radio Shack for less than $20, plus wire. But going that route would presuppose that one knows what the heck one is doing when it comes to relay- and harness-building, which I most assuredly do not.)

The Drake harness contains two relays, one fuse, two female headlamp sockets (connect to new headlamps), and a single male socket (connects to one of the old harnesses’ sockets). And it comes with a wonderful installation “manual”, too.

As it turned out, I also had to buy an additional $3 headlamp socket from O’Reilly. This was because the socket on my factory harness (I chose to use the passenger-side socket) didn’t come close to matching the male socket on the Scott Drake harness. No biggie — just a simple cut-splice-and-wrap removed the original socket and replaced it with a new-style one, which fit perfectly.

I also needed several feet of 14-gauge power wire, which I already had on hand. No matter how I routed the new harness, I could not get the new passenger-side socket to reach the passenger headlamp itself. I tried three different routing combinations, to no avail. So again I had to do the splice-and-wrap thing, adding a few extra feet of 14-gauge wire to the Scott Drake product. Once that was done, I had plenty of harness to make it to both headlamps, with the dual relays and fuse mounted just beneath the battery (pic above). From there, the red power wire from the Drake harness connected easily to the battery side of the starter solenoid, and there were plenty of opportune spots for a grounding connection.

… And The New Bulbs

My upgrade headlamps were a pair of Sylvania H6024 ST Silverstars (12v; 65/55w). These are sealed-beam halogen headlamps, and are currently Sylvania’s “high performance” offering. I purchased them from my local O’Reilly Auto Parts store. Cost was $52 for the pair, plus tax.

Doing the Job

Though it uses the Reenmachine harness (noted above), a Mustang Monthly “Upgrade the Headlights” how-to gave me a lot of assistance. Still, what had been billed as an “easy” job that should take perhaps a couple of hours didn’t quite turn out that way. Most of my time was spent routing and rerouting the new harness, looking for possible combinations that wouldn’t require my extending the passenger side of the harness. Alas, I wasn’t able to find any.

With that, plus a couple of trips to my nearest parts joint (O’Reilly), the harness install took me most of a day.

NOTE TO SELF: In the future, when futzing around with the battery side of the starter solenoid, BE SURE TO GODZILLA TIGHTEN the solenoid bolts! Because without a great, tight connection here, the Mustang will not start — it’ll only buzz at you. Nice job figuring it out the hard way.

The Results? Excellent!

Wow … what an improvement! My first drive with the new headlamps was at a nicely-dark 9pm, and the halogens lit up my neighborhood roads far, FAR better than their predecessors. Now I just need to get them aimed, and we’ll be all set to tackle whatever nighttime driving comes our way!

This entry was posted in One-Day Upgrades, That's Not Stock!, Wiring & Electrical. Bookmark the permalink.

One Response to Upgrade to Brighter Headlights

  1. Michael Green says:

    I doing far more work on my lighting system then you have done. It will also take me much longer. I am building my own wiring harness using 12 gauge high temperate wire. I am using Hella lights with removable bulbs. Hella is a German company that makes lighting systems for high end European cars. They are far better lights than available from American companies. Fortunately, they also make lights to replace sealed beam lights for our classic cars. A pair of Hella lights with high end Halogen bulbs cost about $115. I am also replacing my headlight switch and fuse panel.

    I am replacing all my fuses with plug-in circuit breakers that automatically reset if tripped. That will eliminate the hunting for a blown fuse. My new fuse and relay panel will be mounted near my battery.

    Finally, I am changing the 12 volt source that triggers the relays to turn the lights on. Instead of using the always on source, I am using the source that is only on when the ignition switch is on. The advantage of this is that if I forget to turn my lights off when I leave my car, they will turn off automatically with the ignition switch. This will keep me from running down my battery if I forget to turn off my headlights.

    What I greatly appreciate from your article is the links at the start. They gave me the resources to do this job. I own a shop manual which has proven inadequate for this job.

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