This may seem like a rather odd topic, as changing a bulb is usually a pretty simple and straightforward affair. Why dedicate a whole page to something like that? Well, we wanted to let you know the concours, correct way of doing so.
Nearly all of the bulbs used on the aero Fox Cougar/Thunderbird were halogen. When these cars were new, halogen was the big thing, and Ford used that type of bulb nearly everywhere. The main exception was the headlamps, where halogens were an option (but were standard with the optional System Sentry/"lamp out" system, where halogen lamps were required). These days it's difficult to find a non-halogen bulb, which is actually a good thing. Halogen light is stronger, consistent, and the bulbs tend to last longer. The only downside is that they produce their fair share of heat. But for the most part, Ford allowed for all of this when they designed the lighting systems for our cars.
So it would be very easy for us to say, "Replace any burned out bulb in your car with a halogen replacement" and be done with it. While that's completely true, we did want you to be aware of a few things first.
In the last decade or so, we've seen a multitude of newer halogen bulb offerings that promise whiter light. Pioneered by Sylvania under the Silverstar brand name but equally relevant to other brands, this lighting has a coating on the outside that gives a slightly bluer casting. According to Sylvania, these bulbs last longer and give off a stronger light. We can attest to their claim, especially with headlamps, where typically we can use a little more help. Nearly every bulb in our cars can be replaced with a Silverstar equivalent, including 1987-88 headlamp bulbs. They are more costly (usually twice the cost of a regular halogen), which seems to be the only downside here. We find them to be a very good replacement "upgrade", as they will give new life to your aging system and reward you with better visibility all around. We also feel that they wouldn't penalize you when it comes to judging at car shows, if lighting is even checked. Be sure to use a quality name brand that you've heard of before, and make sure there's a warranty in case of premature failure.
Yes, it's very tempting to go with LED replacement bulbs. Yes, they're plentiful and inexpensive on eBay. But after converting a couple of our own cars with LED lighting, we can say that at this point it's not such an easy thing to do the correct way. The first issue is the type of lighting--not all LEDs give off the same type and quality of light as an incandescent or halogen bulb. LEDs tend to be directional, while the older bulbs are omnidirectional. This creates a big problem with things like taillight bulbs and turn signals that were designed by Ford to reflect light from an omnidirectional bulb. Any LED replacement needs to mimic the stock bulbs, or else you'll see "hot spots" that will diminish the overall light quality and possibly safety.
Even with the right style of LED bulb (which we have found and used), the next issue is the overall brightness. While LEDs can be bright, not all of them will give you better light vs. your stock bulbs. A brightness rating of 5050 or higher is what you'll need to look for. For things like the taillights, you will need to use red bulbs and not white ones. It's a phenomenon unique to LED lighting but if you use a white bulb, the light output through the taillight lens will be pink and possibly not in the legal color range. As a general rule, you need to buy the same color LED as the lens it's going into.
The light range is also critical. As with LED bulbs for your home, the automotive versions also have a light range rating. Ideally, any LED bulb replacements for our cars should be in the 4500-5000K range. This gives off a warm, yellowish-white light that mimics incandescent or halogen lighting and ensures that everything lights up the way it was intended from the factory. The reality is that there aren't a multitude of good, quality bulbs in this light range. You can use 6000K, which is a bright white that borders on blue, but things like the heater panel and some of the digital dash components may change colors when illuminated, which may not be desirable. In fact, some things are overpowered with 6000K bulbs.
And then there's the quality issue. Sure, you may luck out and find a 10-pack of 194 bulbs in the 5000K range on eBay for dirt cheap. But even if they give out the same quality of light as a halogen 194 (which is unlikely), are they going to last? The theory is that LED bulbs last 20,000-50,000 hours. But cheap LEDs typically won't. Many people report flickering, blinking, and premature failure with these cheap, off-brand bulbs. We have used a lot of Sylvania LEDs and can attest to their quality...but they're only available in the 6000K range and up.
So until a quality name brand company starts producing reproduction-style LED bulbs in the 4500-5000K light range, we would suggest sticking with halogens for the time being, if you wish to maintain the stock lighting appearance throughout the car. We suspect that in the future, this will be a common upgrade for hot rodders and muscle car owners, so just sit tight until mankind gets this correct.
Technically, Ford issued different instrument cluster bulbs for things like the digital speedometer illumination. These pointed halogen bulbs were very expensive when new. Typically these bulbs will be in a different colored bulb holder on the back of the cluster, usually light blue or sometimes red. Of course, Ford wanted you to replace that bulb with the same exact kind, but in reality you can easily substitute it with a regular 194 (or similar 168) bulb with zero difference in quality or illumination strength. There is no need to hunt one down on eBay or a Ford dealer anymore.
For 1983-86 cars, he stock-style 4x6 rectangular 4651(1A1) and 4656 (2A1) headlamps are still available for our cars. They are not as inexpensive as they once were, when nearly all cars used them, but at least you can get them.
For correctness, if your car did not have the halogen headlamp option, it may be a a little tougher for you to find a non-halogen headlamp new. Your best bet may be swap meets or even eBay or Amazon. However, at this point you can upgrade to halogen without penalty at judged car shows, as that is what was typically expected of cars from our era.
All halogen headlamps should have "HALOGEN" stamped in the middle of the glass section. All markings and fluting should be as original, complete with "DOT" in the glass. This is how the cars left the factory and how they should also be replaced if this is your desire. Other brands may have different lettering in the glass, such as Silverstars ("PERFORMANCE"). This may or may not be acceptable in serious judging and is your call. We know a few people that switch out headlamps specifically for these types of shows, so that's something to consider. As long as you have four matching bulbs you should be alright.
Be sure to check the bulb reference chart pages for 1983-86 and 1987-88 cars for reference when replacing. Please keep in mind that this information came directly from published Ford documents (owner's manuals, EVTM manuals, shop manuals, etc.) but it may not reflect what's actually in your bulb holder. We have annotated variations that we've found on those pages so that you won't have to guess.
As with all halogen bulbs, any dirt or oil from your fingertips will shorten the life of the bulb. Be sure to use clean mechanics or rubber gloves when replacing them, and be sure to wipe off all excess dirt and oil before you're finished replacing them.