LEDs are current driven, not voltage driven
(well not strictly true
- they do need a certain amount of volts in order to light up, but as you're reading 12V in the dash, that explanation will suffice).
While you're showing 12V, it's possible that there's not enough current getting through.
If something has shorted out causing the wiring in the loom to partially burnout, it may still allow the voltage through but not the amount of required current
- i.e.
the wire is acting as a resistor.
Do you have any idea what current is required by each of these LED bulbs? A check of the supplier's website might yield the answer.
If the bulbs are for example rated for 1 watt, they will require around 84 milliamps
(12V divided by 1 watt
= 0.083 x 1000).
If your power supply cannot deliver this then they are not going to reach their full brightness.
The way to test this would be to use a multimeter in amps mode
(by switching the positive lead into the correct socked
- ensure you put it back to volts etc.
afterwards) and testing it in series with the bulb whilst it is power up
- do not put the test leads across the bulb's terminals, it will short out the connection.
I would do this by finding a way to affic some test wires to the terminals on the bulb bracket
- maybe by using an empty old socket to carefully wedge some wires in place.
I can then use the test wires to hook up the LED out of its socket to test that the connection is good.
Once you're happy with that, remove one of the wires from the LED and hook it back up via the multimeter i.e.
Here's a
(terrible) diagram to make it easier to explain
Once you have it all hooked up, set your multimeter to read milliamps and see what the current draw is.
Note down this result, it should be similar to the specifications but manufacturers have been known to lie a bit about the power output so it could be lower.
One way to be sure is to get a 12v DC power supply and hook one of the LEDs straight up to that with the multimeter also in series.
See how much current it is trying to draw which will give you an idea of the real rating
- ensure the LED is lighting to the correct brightness.
Hope this helps.
It is definitely possible to replace the dash bulbs with LEDs I've been running them for the last five years in my MR2 without issue.
They're the surface mount types and there are around 10 LEDs on each
"bulb".
If you can't make the required current, then I would suspect something is up in the loom or you have a bad connection somewhere.
You really need to get this checked out.
At best
- the already burnt out wires will just burn out quickly and stop working.
At worst, the increased resistance will cause them to heat up, potentially causing a fire.
