Low-Beam Headlight Issues


Help Support 7173Mustangs.com:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Aug 26, 2022
Reaction score
My Car
1971 Pewter Convertible 351-4V
Hello all. I need some help troubleshooting my headlight issues. Currently, I have high-beams only, the low beams don't work at all, not even dim. I have searched for other posts and threads but I've been unable to find anything quite the same.

When I purchased my convertible it already had Sylvania H6024 headlights. They are the sealed headlights only, no extra wiring or relays that I can find. The factory wiring harness looks good, no obvious splices or cuts. All other electrical systems for the tail & brake lights, front & side markers, and the turn signals are all working properly. All of the related wiring looks good.

I have not installed any other light components on the car, my Mach 1 grille and Cibie driving lamps are on hold till I resolve the lo-beams issue.

The headlight switch does appear to be working and it feels solid switching thru all three positions. All grounds are good. So far I've only had some time to look for visual and obvious issues, I have not run a meter over the switches or harnesses.

I thought it might be a faulty dimmer switch or an issue with the headlight switch. I'm going to replace the dimmer switch first, it's simple and easy to replace. I'll move to the headlight switch next if the dimmer switch doesn't resolved my issue.

Any suggestions would be greatly appreciated. I'm sure I'm overlooking the obvious and selfishly hoping for an easy fix :cool:.
IMHO you have identified the two most likely culprits. Far be it from me to second guess our local expert "shorts checker" for the first component to trouble shoot!

That said, I'd strongly recommend you think about installing a set of headlight relays. Getting the load off the old switches and wiring does wonders to improve headlight function. In a similar vein I have found installing a horn relay really brings the horns to life.

There are plenty of places in the engine bay to hide the relays and wiring for a full stealth system to keep things looking original.
Bad dimmer switch. It routes the headlight power from the main headlight switch, thru the dimmer switch to high or low beam headlights.
I agree with our "Shorts Guy" and Idaho Chris. Plus maybe change the headlight switch as well, just to be sure.
Now would be the perfect opportunity to upgrade to Hella lamps and 9003 type LED's WITH relays. There are other brands on the market, Holley, for instance, sell a very expensive LED lamp via vendors like NPD, but at around 215 bucks A PIECE.
You could do both sides with Hella lamps and LED's for less than that.
Then of course you would want to buy a set of my latest LED headlight water shields, (soon to be released) because unfortunately on our cars, water can get in should you get caught in a rain storm, or just washing your car.
Also, I have put together a pdf to show how to construct a better relay set than offered on Amazon. This is with the blessing of Bill at HiPoParts.com (www.), who supplied me with all my relays and connectors and ALL my Led lights with the exception of the 9003's
If you want more info, please PM me (conversation as it's now called).
Randy, Chris, Racer, Geoff - thanks gents I appreciate the help and the confirmation on my plan. Currently, I just need to get the car to pass inspection so I can get it registered. Hopefully I can find a couple minutes this weekend to switch out the dimmer switch. Luckily all small-world problems to date.

Yes, a full lighting upgrade is in my future and I will definitely be looking to you guys that have already successfully upgraded for the best solution.

Latest posts