The good news is that the on-and-off headlight cycling provides you with some measure of intermittent nighttime visibility. The bad news is that unless you replace your headlight switch soon, you'll find yourself driving down a dark highway with no headlights at all, putting your treasured vintage Mustang at risk. But there's more good news because it's relatively easy to replace an aging or faulty headlight switch, especially if you understand the procedure.
Vintage Mustangs essentially...
Vintage Mustangs essentially used the same headlight switch throughout the ’65-’73 model years, with various spacers used to adapt the switch to the different instrument panel shapes. National Parts Depot offers several versions of the switch, both original and reproduction. For our ’66 Mustang, we ordered an original switch, which cost more but has a reputation for being more durable than less expensive reproductions.
As Senior Editor Jim Smart pointed out in his informative "How to Troubleshoot and Service Headlight Switches" article in the June '10 issue, '65-'73 Mustang headlight switches are prone to corrosion as they age, which takes a toll on the switch contacts as heat builds through high resistance. Headlights are high-load electrical components, so they draw a lot of power, causing the switch to get warm. With new switches, the heat isn't a problem because the circuit breaker and contacts are clean with good continuity. But as switches get older, the heat causes the circuit breaker to do its intended job--cycle the headlights off and on. More powerful aftermarket headlights draw even more power than original-style headlights, exacerbating the problem.
If you experience flashing headlights, then it's time to replace your headlight switch. Thankfully, the procedure is fairly basic for vintage Mustangs. Here, Merv Rego at Classic Creations of Central Florida is replacing a faulty switch in a '66 Mustang, but the R&R is similar for other Mustangs.
1 Access varies by Mustang...
1 Access varies by Mustang generation, but with ’65-’66 Mustangs, removing the instrument cluster aids access to the headlight switch behind the instrument panel. No need to disconnect the gauge and light bulb wiring for complete removal; just disconnect the speedometer cable so the cluster can be pulled away from the opening. As always, it’s a good idea to protect the paint on the steering column by covering with a shop towel.
2 Turn the headlight switch...
2 Turn the headlight switch knob and shaft assembly counterclockwise (all the way past the interior light turn-on point), then press the small button on the side of the headlight switch (opposite the wiring plug) and pull the shaft out. Because the button is hidden from view, you’ll have to feel around for it (see photo 6). If accessible, reach behind the instrument panel to disconnect the wiring harness plug. If access is tight, you can disconnect the plug after the switch has been loosened and pulled away from the instrument panel.
3 NPD offers a dash bezel...
3 NPD offers a dash bezel tool for removing the ’65-’66 headlight switch bezel stem nut. You can remove the nut with a flat-blade screwdriver but the tool reduces the chance of damage to the nut and bezel. In fact, we could see evidence that our stem nut had been removed by a screwdriver in the past.
4 Remove the stem nut from...
4 Remove the stem nut from the headlight switch.
5 Once the stem nut is removed,...
5 Once the stem nut is removed, maneuver the headlight away from the instrument panel and remove.
6 With the headlight switch...
6 With the headlight switch out, you can see the button used to release the knob and shaft assembly.
7 A quick comparison of the...
7 A quick comparison of the old switch and the new switch revealed that we had ordered the wrong switch for our ’66 Mustang. While the actual switch is the same, the short spacer is for a ’65 application. Thankfully, Merv had a longer ’66 spacer in stock.
8 With the spacer held in...
8 With the spacer held in place with a couple of dabs of windshield sealer, the new switch slips into place behind the instrument panel.
9 Use the bezel tool to install...
9 Use the bezel tool to install and tighten the stem nut, then plug in the wiring harness.
10 Push the knob and shaft...
10 Push the knob and shaft assembly into the switch until you hear the “click,” which indicates that the shaft is locked into place. Double-check by pulling and pushing the knob.