I don't believe it can. The stock dimmer resistance is not ranged for LED's. My theory below...
The dimmer rheostat in my 96 SCSB controls the current to 6 194 bulbs, the radio bulbs, and A/C control bulbs.
A 194 bulb draws 3.8 watts. Forgetting about the radio and HVAC bulbs, the 6 194 bulbs on the dash are ran in parallel so the current through them is additive. I don’t know what the minimum wattage on a 194 bulb would be to lightly dim it behind the dash or even look as to be off, but let’s say 2 watts. Power in watts is equal to voltage in volts multiplied by the current in amps. And resistance in ohms is equal to voltage in volts divided by the current in amps.
Watts=Volts x Amps
Ohms=Volts / Amps
So, when the dimmer is set to bright, six 194 bulbs in parallel drawing a total of 3.8 watts each is a total of 22.8 watts with .27 amps through each one. With 14 volts supplied, this means all the bulbs together are drawing 22.8/14 = 1.63 amps current. The rheostat dimmer resistance to provide a total 1.63 amps then divvied out to all the bulbs in parallel is 14/1.63 = 8.5 ohms.
When dimmer is set to low brightness , let’s say 2 watts is what each bulb is drawing in power. Doing the same math means the rheostat increased resistance to limit the current down for dim bright is around 16 ohms.
All this to say the dimmer in the truck is probably got a rheostat with about 18 or so ohms down to some small ohms (8 ohms) for max bright.
An LED doesn’t work like an incandescent bulb. It’s a diode so the current only flows in one direction across it and its current has to be limited on the order of milliamps or it’ll burn out. Something like 20 milliamps of current. That’s .02 amps. Depending on the LED color, the diode has a forward voltage drop of 1.8 to 3.3 volts when lit. Across the diode is going to drop from 14 volts by this amount. Let’s say the LED forward voltage drop is 2 volts. So, in sizing a resistor, it’s 14v – 2v = 12volts, then 20 milliamps into that is 600 ohms. 600 ohms would provide .02 amps to an LED with a forward voltage drop of 2 volts, on 14volt supply.
With a 14 volt supply, the LED has to have a resistor in series with it of around 600-700 ohms in order to keep the current to .02 amps, and that resistor is going to be buried into the LED bulb pack if your buying 194 or 74 LED replacement bulbs. Nobody is going to sell you 194 or 74 LED bulb replacement without a resistor in there because they know without the resistor you’ll install them and blow them out.
To dim the LED to a point where it would look deeply dimmed, the current would need to drop to like 1mA, or .001 amps. But the LED isn’t reliable then and flickers on/off or strobes, or just turns off etc.
Watch the first minute of this video
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From the standpoint of the circuit, the 6 600 ohm resistors of the LED’s in parallel is the same as a single 100 ohm resistor representing the parallel LED bulb bank. The problem with trying to dim the LED is that with a rheostat dimmer that goes from 8.5 ohms 18 ohms, the total available resistance to dim is about 118 ohms. 12 volts / 118 ohms = .1 amps and .1 amps / 6 LED’s = .017 amps. 17 milliamps dimmed vs. 20 milliamps bright. Not a very deep dim even though dimming is occurring, but not noticeable.
Better dimming might be possible with a wider range adjustable resistor but even then it would have to be put in as a separate device adjustable from the dash. A fixed lower brightness could be achieved by changing LED resistors if possible.
I suspect the superbrights.com LED’s might dim, but not very noticeable and then they go dark. The best way to dim an LED bank is with Pulse Width Modulation but that is a whole other topic.
