Mike, the other forum post for adding the fuse link specs a 3amp fuse because it assumes you are using the stock 2watt bulbs and 8 bulbs at 2watts each will draw about 1.5amps total, so a 3 amp fuse is plenty. However, we are using 5watt bulbs and 8 of these draw about 3.4amps which will clearly blow a 3 amp fuse very quickly. You could start with a 5amp fuse and see how it goes. After re-thinking the fuse size I'd say 5 or 7.5 amp would be just fine, 10 amp may be a bit large for our purpose. I will update my prior post to 7.5amp.

Sal, we need to remember that the bulbs are in parallel. Based on a 14 volt supply and 5 watt rating they should be drawing .35 amps each and have a resistance of about 39 ohms. The equivilent resistance of 8 bulbs in parrallel is 4.875 ohms. Based on that same 14 volt supply voltage the current draw is 2.87 amps. I think a 5 amp fuse would be plenty.
Back to the dimmer having a 5 ohm resistance. If it is in series with the 5 ohm equivilent resistance of the 8 bulbs looks like the current draw would be 1.5 amps to the max of 2.87 amps, based on the dimmer setting... Or is my math flawed?

Ron,

Your math at 14volts is correct, here is my calcs at 14 volts:
1 bulb is 5watts so 5w/14v=0.36a
8 bulbs would be 0.36a X 8 = 2.88a for 8 bulbs.

BUT, we must also calculate current at 12v or even as low as 11v because you can power up the gauge lighting with the car not running, so what if you left your lights on and walked away from the car?

So at 12v the numbers are like this:
1 bulb is 5watts so 5w/12v=0.42a
8 bulbs would be 0.42a X 8 = 3.36a for 8 bulbs.

Also keep in mind that the dimmer circuit not only feeds these 8 bulbs but a few other 2w bulbs as well, like the hazard/flasher light, heat lights between seats and the fresh air controll in the dash, may have missed 1 or 2 others.

As for the 5ohm dimmer it is wires in series with the bulbs but when lights are fully one (turn dimmer clockwise till it clicks) then the dimmer is out of the picture and full battery voltage is sent to the gauges.

So, I agree 5amp would work fine but keep in mind the harness is actually good for about 8amps this means fusing it with 7.5amp is also OK. But to error on the safe side I'll agree with 5amps as a starting point since it's better to have us blow a 5 amp fuse and then bump up if need be.

So, I'll revise my post to 5amp fuse link.

Thanks, Ron

Agreed! I was trying to get a feel for what the current was originally with the the 5 ohm dimmer resistance and the 10 or 12 -2 watt lamps. I guess i need to go back and count up all the bulbs on that circuit. I'm betting the OEM config also made the dimmer get toasty.

Ron, I agree with Toasty dimmer if you dim the dash half way or more with stock configuration. But who ever dims the dash in these 911s? I don't. But my bench test had the dimmer very toasty around 1.8amps with dimmer 1/2 way dim or more.

Thanks for the explanation Sal (and Ron). I completely understand the reasoning behind the fuse size now. (sorry if I'm a little slow...:p )

sub

I bought some white led's from someone on ebay. They put out a slightly brighter light, but you can not dim them. So far I'm appy with them but would like them to be even brighter.
I think with the white gauge kit they would be much brighter.

As noted earlier in this thread, just replacing the tired/smoky bulbs with all fresh goodness can make a huge difference. I changed out all of mine, and am happy with the results.
(This from the guy who got in trouble for cutting up christmas lights to put in spaceship models when I was a kid)
I'd like to bypass the dimmer completely (cooler and brighter?)
Anyone have the pinouts?

Just page up in this thread a little bit to see a picture of the back of the headlight switch. It shows what to relocate so that the dimmer is bypassed. The dash gauge lighting is the black/blue wire that's is shown disconnected. just move it over to the adjacent post with the white wire. So you will wind up with the black/blue wires on the same post with the white wire. I also suggest you put a 5amp inline fuse on the black/blue wires while your at it. The dash lighting circuit does not have a fuse and is only fused by the headlight 30amp (not 100% on this amprage but it's very large fuse) this presents a issue that if a short where to happen in the gauge lighting you could have a dash fire. For this reason many folks like to place a 5amp fuse on the dash lighting circuit (black/blue wires).

Good luck.

Hey Sal,

Any updated pics yet of your dash?

bump

it lives... Sal, would still like to see updated pics of your gauges when you can...

Ron, I just wanted to see a set of gauges that had undergone the complete "treatment" described earlier in the thread... Does not matter whose car...:D

Think carefully before going the LED route. Some people, including me, find them way too bright. And I'm told they can't be dimmed.

moneymanager,

The brightness of an LED is based on the amount of current running through it. If they are too bright, you need a different current limiting resistor.

Ah. Thanks. Helpful.

I did post a few pics of my updated gauges, although the pics suck pretty bad. However, it is a marked improvement. I've been very happy with them. I can actually see my gauges at night without staring at them. No problems, and they've been in the car for at least 6 months now. Much of my driving is at night too.

Does anyone know which bulbs these are? I just bought some leds and look nothing like these. Are these the 4 bulbs? I also have white gauges. Any help is greatly appreciated guys. Many thanks. :)

Sorry, it's this one above. :)