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Discussion Starter #1
Hi,
I'm new to Fords after about 1984, but no stranger to old pickups in general.
While the wife and I were driving home last night after trimming a bunch of horses far far away, we finally got out far enough in the sticks (i.e. close to home) to use the high beams. They came on, blinked a couple times, then went out. Marker lights stayed on. Switched back to LOW and all was well. Switched back to HIGH with the same result as before.

So.... my question is, headlight switch or dimmer switch? Which is more likely? Or should I just replace both?
Headlight switch knob and the bezel behind it were warm (though nowhere near as hot as a couple 1stGen Dodges I've owned through the years), which leads me to think headlight switch, but with it only being a HIGH beam issue, I could see it being a dimmer issue.

Thanks in advance
 

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I had the same issue a while back. It turned out to be that the connection had simply come loose at the multi function switch. I tightened it up, and stopped the trouble completely. I would start with the dimmer switch, and go from there
 

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Don't just throw part$ at it. Original parts are generally better than new ones. Both those switches are known to have problems, but that doesn't mean chinese replacements are perfect. The headlight switch is known to burn its terminals inside the connector shell. Sometimes, just the 1 burned terminal & the plastic shell must be replaced (using a common, cheap, parts-store pigtail). In other cases, the switch must also be replaced.

This photo album explains how to rebuild the MFS, but if it's burned internally, just replace it (with the BEST one you can find - NOT the cheapest):

(phone app link)
 

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Discussion Starter #4
My wife was a service advisor for 8 years. When possible. I buy OEM or better, ESPECIALLY if it has a wire attached. I'd rather buy NOS than parts store china-junk
 

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OEM refers to the manufacturer - not the part. And even the manufacturer doesn't always build compatible parts the same way 20 years later, if that manufacturer is still in business, and if you can identify who the OEM was. It wasn't Ford or MotorCraft because they don't build any parts.

NOS refers to the part, but it doesn't say who built it. Ford can have 10 suppliers for 1 assembly-line (OE) part, and 40 different suppliers (over the following 20 years) for replacement parts; any of which might end up on the shelf as NOS.

But occasionally, OE & OEM parts aren't the best. Sometimes, they have a known problem that makes them a poor choice for replacement.

In any case: you can't even guess if a replacement part is needed until you know what the problem is. And that takes diagnosis. Have you looked at either switch yet?
 

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Ford runs the full power of the headlights through the switch without the use of relays. That's a good amount of amperage, especially on high beam. OEM switches always seemed to start burning up after 5+ years, had one actually start smoking!... until I modified the headlights to run off of relays instead. The light switch now only has a small load running through it as it only powers the relays now. Haven't had any issues with the switch/headlights in over 10 years now.

You can build the modification from scratch pretty easy.. or even easier their are a few companies that make plug and play kits that drop right in.

1993 F350 Crew Cab Dually
XLT
7.3 Factory IDIT w/Banks Sidewinder
5spd Manual
 

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Discussion Starter #7
Thanks, guys. I confirmed this evening that it does indeed need a new switch. My fuel tank switch is kinda sitting behind the fascia. After the lights went dark, I reached around to feel the switch and singed my finger tip. (I'm a blacksmith so it didn't ruin my day).

I wasnt sure if Ford ran relays for headlights or not. Relays are definitely on the list, then. Not only do they take load off the switch, they also brighten the lights😁.
 

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That would be true if these trucks rolled of the assembly line with hot switches. But they didn't. Something has changed about your truck's wiring in the past 22 years, causing that. The most likely cause is simply oxidation of the headlight switch terminals (outside) & contacts (inside). A quality replacement switch should restore the headlights to original brightness, and the switch should last another ~20 years. If not, there's some other problem that needs to be fixed. Adding relays may bypass that problem, or cause several new problems to appear (maybe after a while).

Both my trucks ('93 Bronco & '95 F150) still directly power their headlights through their original headlight switches. And they both still use common halogen bulbs, similar to original.
 

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OEM refers to the manufacturer - not the part. And even the manufacturer doesn't always build compatible parts the same way 20 years later, if that manufacturer is still in business, and if you can identify who the OEM was. It wasn't Ford or MotorCraft because they don't build any parts.
Obviously you never worked in a dealership. FoMoCo may not build any parts but all their vendors have to meet Ford's specs. And Ford (Motorcraft) parts are generally top of the line but not always. A perfect example was the dash mounted pre'92 headlight switches which wouldn't carry headlight/taillight amperage. Over a period of years they continually overheated and malfunctioned. However, Napa carried two switches, the more expensive Echlin switch would carry more than enough truck and trailer amperage and never burned out.
DPfarrier, if your '93 has the same dash mounted switch, as pre'92 rather than wire in a relay you might get the Echlin switch. I had to install one about 20 years ago and I pull a 3 horse gooseneck, flatbed gooseneck, and travel travel with LOTS of lights and still using the same switch.
 

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Obviously you never worked in a dealership.
Several, including a Ford dealership.
...all their vendors have to meet Ford's specs. And Ford (Motorcraft) parts are generally top of the line but not always.
I agree. But Ford/MC parts aren't MADE BY Ford or MC. And there can be 20 vendors for the same part going to one or several assembly lines; and it's possible that none of them is still in business or making the same part the same way 20 years later. So the Ford/MC part he buys today is not necessarily at all similar to the OE part. That was my original point.
...the dash mounted pre'92 headlight switches...
The same headlight switch DESIGN (& probably specs) were used from '87-96/7 F-series & Broncos (and beyond on vans). 6C2Z-11654-A
Over a period of years they continually overheated and malfunctioned.
In my experience, it was only a few of the '92-up switches that burned off the terminal for the Tan/White wire, which supplied the parking (Br) circuit and the dimmed dash (LB/R) circuit. But I have at least 4 original '93-96 switches that haven't; 2 are installed in running trucks.
 
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