Dan Cobb

For those considering an LED conversion, I wouldn't bother unless you plan on installing several additional lights in each gauge (as they do at a very reputible speedometer shop for about $300!).
I used a 10mm high output blue LED ont he clock and it was as pitiful a the original bulb, except it was blue.

I have created a method of brightening the gauges though using off-the-shelf components.
My local radio shack has bulb sockets that fit the Sylvania 3893 (T4W) bulbs.
They slip right into the original holes on the back of the gauges, & they are at least twice as bright as my original bulbs.
You will have to clip the black/blue wires and remove the BA7 sockets from the harness, but not such a bad sacrifice for being able to now see the gauges at night.
I added an extra hole to the 6:00 position on the clock and installed a second bulb. It allows you to actually see the numbers between 3 and 9.

I'll post more info once I have a final version integrated into the factory harness, as I have not determined the best method of attaching the new sockets to the backside of the gauges where necessary (i.e. the second hole on the clock).
+++

98carrera4S

Dan, I've been contemplating installing LEDs in my dash cluster lately as well...it's pitiful how dim the factory lighting is. I had a couple of questions for you:

1. Do you know what kind of OEM bulbs the 911 uses, and how many are needed? I haven't taken my dash apart yet, and would like to be able to order the bulbs before doing so.

2. Did you use wide-dispersion angle LEDs? Incandescent bulbs emit light in every direction. LEDs are semiconductors and typically emit light in a more narrow, focused beam (sometimes as little as 10 or 15 degrees). Getting a bulb with a wide dispersion angle is key to getting uniform lighting across the instrument face.

For what it's worth, in doing my research, the two most promising wide-angle LEDs I've come across for dash applications are radial LEDs: http://superlumination.com/images/au...matrix_lit.jpg and inverted cone LEDs: http://superlumination.com/images/auto_bulbs/194iw.jpg. I'm not sure if these will fit in the 911's dash light base (both are 194 bulbs).

Please do post updates as you experiment with on your T4W bulbs. I'm not hung up on installing LEDs - like you, I just want my dash to be much brighter than it currently is. I'd love to see before and after pics when you're done. Thanks.

Dan Cobb

1- OEM bulbs for the gauges are a European (DUH!) BA7. It looks similar to the T4W, but instead of round pins to hold it in place, they have 'wings' and are smaller in diameter.
I believe you will need 9 bulbs for the gauges.
The heater/fan control, & the fog light/rear defroster ***** have the smaller 2721s (or 2723s).
You will need 5 of these.

2- The LED that I tried was a 10mm high otput w/ a 25° viewing angle. Part of the issue is how far the face of the gauge is from the mounting point of the light. There is a small 'tube' on the back of the clock that the light goes in. This tube is nearly an inch or so long, placing the light too far behind the face to do much good on the bottom of the gauge. The larger gauges have multiple lights, but they are still less than adequate for uniform illumination.
I tried a colored sleeve over the T4W bulb and it provided a great blue color that was uniform and bright enough to see the entire clock.

I'll be picking up a few more parts today to hopefully complete at least 1 gauge this weekend.
+++

98carrera4S

Thanks Dan. I'm looking forward to hearing how the install goes this weekend. Please post pics if you can. By the way, I noticed some BA7 wide angle LEDs on this site: http://www.superbrightleds.com/cgi-b...ct=CAR&next=50 (scroll to the bottom of the 2nd page)

Not sure if these are the ones you tried, but I thought I'd pass the link along in case it's helpful.

Dan Cobb

Very interesting. I actually bought up a bunch of loose LEDs and resistors and made up my own "bulb".
I like their packaging (it appears to be almost the same exact size as the original bulb), but I suspect the issue of angular dispersion (for lack of correct terminology) of light from the LED will be significantly inferior to the incandescent bulbs.
For $0.89 each, it would certainly be worth a try though. I'll have about $30-$40 plus a bit of trial-n-error time invested into mine when it is finished.
Hopefully it will be a bit brighter than stock though.
BTW, FYI: It is possible to have an effective dimming circuit for the LED applications, BUT (BUT!) the potentiometer must have a very accurate, very narrow range, and it must be wired in series with an appropriately sized resistor to drop the voltage to the maximum rated value for the LEDs selected. (usually around 3.8VDC, but some operate as high as 5.0VDC) The potentiometer needs to add to the fixed resistor to drop enough voltage (usually only 1-1.5VDC) to dim the output.
The problem with simply replacing the factory bulbs with an LED such as those pictured is that the resistance in the potentiometer of the headlight switch is too high, too fast to make it effective as a dimmer. It essentially becomes an off switch at only 1/8th of a turn.
+++
+++

98carrera4S

I can definitely see how this might be necessary if you're using "loose LEDs" to build your own light source. Standard LEDs use a fraction of the current draw of 12V OEM light bulbs. However, if you use 12 volt LEDs designed specifically for vehicle applications (like the ones sold at www.superlumination.com or www.superbrightleds.com , your dimmer should work as before. I actually replaced the dash lights in my wife's Nissan a few weeks ago with 12V LEDs that I bought from SuperBrightLEDs (...as a dry run practice exercise for the Porsche :-). We still have the full range and sensitivity in brightness adjustment using the factory dimmer control. I think it's because these LEDs use the same 12V of voltage as the factory bulbs, so it becomes a straight drop-in replacement application.

I hope your install went well this weekend! Please let me know where you ended up once you're finished. I'm hoping to swap out my Porsche dash lights at the end of July, and hope I can benefit from your experience.

Dan Cobb

So far I have had the time to replace only the outer 2 gauges' bulbs.
Here's something interesting I figured out; the 'tubes' mounted on the backside of the gauges (which actually hold the lamp and socket in place) have nearly the exact ID as the T4W socket OD. This means that you can actually 'press fit' the T4W sockets into the back of the gauges and get a good ground w/o making additional modifications to the OEM wiring harness, or making your own ground wires. I just clipped off the original BA7 socket and crimped (this is a temporary connection for now to determine the value and worthiness of the entire project) on a short lead that I had soldered tot he center pin of the socket.
I am happy enough with the results that I intend to make additional progress on the remaining bulbs as time permits.

As far as the LED dimmer goes, I found that there are at least 3-4 different forward voltage ratings for the majority of LEDs available, each being somewhere between 3.2 to 5.0 VDC.
If you determine the resistor value required to provide the highest rated forward voltage (small resistor value, thus making the LED brighter), then adding additional resistance through the factory dimmer switch will probably be effective.
If you increase the value of the resistor (dropping more voltage, thus making the LED dimmer), then adding additional resistance through the factory switch will likely provide very little dimming ability before simply turning the LED off. This is because the accuracy of a 25 year old (or more!) dimmer switch is simply not tight enough to make a very fine adjustment, which is needed to control the lower voltage LED.
The advantage of using a higher resistance in the beginning is that (if calculated correctly) it will not over drive the LED and blow it up.
Many LED manufacturers provide a maximum forward voltage rating that is still somewhat conservative, but probably not by more than 10-15% of the rated amount. At 3.4V, that would probably be no more than .50 V, and I would think the factory switch is a bit too 'crude' for adjustments much finer than that.
I am far too willing to err on the side of not blowing out my dash lights, than to over drive them.
I'll bet that the switch in your wife's Nissan is solid state, whereas the 911 switch has a winding of copper wire and an armature.

Anyway, I'll try to get a few pics this week.
+++

98carrera4S

Really insightful comments, Dan. Thanks. I hadn't thought about the 911 not having a solid-state dimmer switch. BTW, I did a quick Google search on 3893 bulbs and came across this article on a Ferrari site: http://www.ferrariclub.com/faq/dashlights.html. Nice to know that Porsche owners aren't the only European exotic owners to suffer from dim panel lighting :-). The interesting excerpt in the article is:

"If installing these new bulbs still doesn't make your instrument lights bright enough, you may want to bypass the dimmer switch. Some 308 owners have measured up to a 2 volt power loss through the dimmer switch, and bypassing the switch has produced much brighter instruments. Using the following procedure will render your dimmer switch inoperable, but most of us keep our dimmers at full power anyway and the procedure is simple to reverse if needed."

If the upgraded lighting on my 911 still isn't bright enough, I may try disabling the archaic dimmer to see if it makes a difference. I've never used the dimmer on anything less than the maximum setting on any car I've owned, so the loss of the dimmer control isn't likely something I'll ever miss.