OK, I've done the search, but I didn't find what I considered a match to my symptoms: ('96, no "special" features) I have no low beams. Both went out at the same time... I have high beams (turn signal lever forward) and I have "flash to pass", but no low beams. Main headlight switch? "dimmer" (turnsignal combo) switch? Someone had a problem where one headlight burned out and took out the other one... a possibility? I'd like some opinions before I start taking things apart... THANKS for any replies.

 

The last time my 90 Aero took out both low beams at the same time. But they are sealed beams

 

Guess I could try checking the headlight socket with a voltmeter. Looking for 12V on low beam... Does anyone know if both beams are on when the high beams are on?

 

i think the low beam goes off when the hi beam clicks on. but both lo and hi stays on when you flash and not click the lever into position.

 

Brian--Simply go ahead and pop the clip and remove one of the bulbs. Not hard justa pain in the a$$. Look closely at the filament. If it appears that one of the two wires is burnt out it probably is both bulbs that are burnt out. Go ahead then and look at the other one to confirm if both are bad. A good rule of thumb though. Don't forget to wipe your bulbs after handly the old ones getting reused or while installing the new ones with rubbing alcohol. The grease from your finger tips will leave oil on the glass which in turn will cut the life down considerably. The other method is to simply use a clean lint free cloth. Let me know how it turns out. Its rare, but they do burn out on occasion together from time to time. Mine happened this way.--Respectfully Boz

 

Both of my low beams burned out at exactly the same time. One of the bulbs was about 9 months' old, the other was many years' old - possibly the original. Others have reported similar occurrences, so there must be more to these simultaneous failings than mere coincidence - but I don't know what.
Anyway I replaced both bulbs and they've been fine for several years now.

Jan Richter

 

My first set of lights died within a couple of weeks of each other. I was impressed with how closely the two bulbs were constructed. But if they were not of the same age, and blew at the same time, I would start checking your voltage regulator.

 

hitting potholes at speed will also kill headlights, both at same time
shock breaks hot filament

old straight axle pu's on logging roads are death on headlight

 

I've had both high beams go out at the same time, but the Aerostar was the only vehicle I'd ever had that happen on. Check to see if the bulbs are physically blown in low beam. It could be just a coincidence that both burned out simultaneously.

But if the bulbs are intact, then I would go back to the hi/lo switch on the steering column. The main switch should just feed the hi/lo switch, so if one function is working, then chances are that the main switch isn't the issue (but don't rule it out entirely). I'm not familar enough with the Aerostar's wiring to know whether or not Ford relayed the headlights, but I'm going to operate under the assumption that they did not since it wasn't common practice for them at that time. If that's the case, current is routed from the battery to the fuse panel, to the main headlight switch, to the hi/lo switch, and then finally out to the lamps themselves. That's not ideal for two reasons: 1) it makes for a very long circuit, in which significant voltage drop can occur, and 2) routing all the lamp's power through the interior switches is potentially damaging to the switches over a long period of time (like 11 years). That will eventually burn the switch out. I've seen this on other cars - in fact, I still carry spare headlight switches in my Mazda's glove box (and have gotten good at changing them quickly).

The solution to fix both aspects of that problem is to rewire the headlight circuit to run relays for both the high and low beams. The distance between the battery and the lights is short, and mounting the relays on the core support between them is pretty easy. This keeps the main headlight current circuit very short, and if you use a suitable gauge wire, then voltage drop should be next to nothing (voltage drop is bad because it reduces the light output of the bulbs significantly). This also helps the hi/lo switch because it reduces the current through it from about 9.5 amps to just whatever the relay needs to signal it to trip.

So basically, if it appears that it is a problem with the switch, then first replace the switch (obviously), but I'd suggest then protecting the new switch by adding relays to the circuit. In fact, I'd highly recommend that anyone who owns a vehicle without headlight relays to rewire that circuit. It's easy to do, you can even buy kits to make it plug and play.

 

One other thing that breaks filaments is slamming the hood too hard. If the filaments had many hours on them already, a good slam could snap them at their weak spots.

You can pull a used bulb (9004 or 9007 types) and take a close look at the filaments. On the low beam filament you can see globs of metal built up from the halogen cycle. Yes, the evaporated metal is being deposited back onto the filament, but almost never where they boiled off from, so there will be weak spots.

 

Pulled a bulb... Visual was OK... No obvious broken filiment or discolored glass. Checked with ohm meter, dead short on one set of pins (center to one side) open circuit on second set. Turned on the lights, saw 12V at the plug. $21 dropped at shmucko's auto parts, and we're golden! THANKS to all that replied!