1956 LED Instrument panel dimmer solution.

[lichau]

I decided to replace the instrument panel lights with LEDs. Worked fine, brighter and whiter. However, dimming doesn't work, at least with the LEDs I used. The light switch rheostat expects to be driving about ten incandescent bulbs at about 3W each--full brightness. The LED's consume a lot less than that. I found my LEDs dimmed to zero at about 8V. With the stock set up, full dim on the rheostat driving the panel with LED's is about 10.5V-- at which level the LED's don't appear any dimmer.
Being a long-time design engineer--electronics--I am adept at coming up with complicated solutions to simple problems. Visions of apps on my phone to dim the panel, and various other things were dancing in my head. Then I got talked off the ledge.

I found that a 25ohm resistor to ground on the instrument panel light string (red/blue, I think) simulates the incandescent load nicely. The panel lights extinguish about five to ten degrees before you get to the full clockwise.

The resistor is going to dissipate about 3-4W. Power resistor wattage is usually at a pretty high temperature. I put together a 23 ohm resistor out of four ten watt resistors I had in my junk box and the temp is OK. Bolted it to the dash cross brace.

You could put in a 10-20 watt incandescent light--if you could find one and didn't mind having your feet lit.

I am confident someone will have a more elegant solution. But, mine works. Off to the next issue.

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[cokefirst]

I decided to replace the instrument panel lights with LEDs. Worked fine, brighter and whiter. However, dimming doesn't work, at least with the LEDs I used. The light switch rheostat expects to be driving about ten incandescent bulbs at about 3W each--full brightness. The LED's consume a lot less than that. I found my LEDs dimmed to zero at about 8V. With the stock set up, full dim on the rheostat driving the panel with LED's is about 10.5V-- at which level the LED's don't appear any dimmer.
Being a long-time design engineer--electronics--I am adept at coming up with complicated solutions to simple problems. Visions of apps on my phone to dim the panel, and various other things were dancing in my head. Then I got talked off the ledge.

I found that a 25ohm resistor to ground on the instrument panel light string (red/blue, I think) simulates the incandescent load nicely. The panel lights extinguish about five to ten degrees before you get to the full clockwise.

The resistor is going to dissipate about 3-4W. Power resistor wattage is usually at a pretty high temperature. I put together a 23 ohm resistor out of four ten watt resistors I had in my junk box and the temp is OK. Bolted it to the dash cross brace.

You could put in a 10-20 watt incandescent light--if you could find one and didn't mind having your feet lit.

I am confident someone will have a more elegant solution. But, mine works. Off to the next issue.

Interesting story. I used to work the chat line for a vintage parts supplier and I had many people tell me they wanted LED dash lights. I told them that the ones we sold could not be dimmed, and most did not buy. I wondered if some electronics guru would come up with a solution.

 

[cougarsunlimited]

LED dash lights can be dimmed, without a load resistor, using a PWM (pulse width modulation) controller such as the Auto Meter 9114.
Note: the unit must be a high-side controller because the lights and the power source use a common ground.
PWM controllers that have a separate ground will not work (2 wire input, 2 wire output).

 

[paul5456]

The dash lights in my 56 are really good so I havn't changed them for LED's/ But I did change the ones in my 54 Ford as the dash lights were terrible. The LEDS are great. I like bright lights in my dash, regardless of what car it is, so I don't miss the dimming feature.

 

[Ward 57]

The dash lights in my 56 are really good so I havn't changed them for LED's/ But I did change the ones in my 54 Ford as the dash lights were terrible. The LEDS are great. I like bright lights in my dash, regardless of what car it is, so I don't miss the dimming feature.

Since I rebuilt the cancelling feature I know the blinkers are working and cancel properly even though during the day especially with the top off the green indicators are almost useless but I can hear the flasher clicking.