Vintage Gauges, headlight switch dimming feature?

[Jeff_J.]

I have the FF headlight switch and have connected it the harness - I was expecting the rotation of the knob would adjust the back-light on the gauges, the switch works correctly to turn on the lights.. Maybe I have a faulty switch or is the dimming feature not connected to the gauge lights.. Thanks Jeff_J

[facultyofmusic]

The "dimming" of the gauges is designed to work on older incandescent bulbs that gives off different brightness depending on the voltage supplied to it. The gauges supplied by FFR use LEDs which do not behave the same way. They just "turn off" if the voltage is below some threshold.*

There are things that help you "dim" an LED tho, such as PWM controllers that convert input voltage to a PWM signal that effectively switch the LEDs on and off really quickly to make them seem dimmed.

* Technically they don't "just turn off" but the range of transition is small enough that for what the knob lets you control, it effectively "just turns off".

[Jeff_J.]

Ok, makes sense the FF switch was intended for incandescent. I think the real answer here is the Headlight switch does not control the light intensity of the Gauge LED's. I'll look into a dimmer specific for the gauge lights - I'm sure speed hut can help here. Thanks for the input.
Jeff_J.

[John Ibele]

The vintage gauges come with their own PWM dimmer. It's on the left in the picture on p. 61 of the harness installation manual Rev W.

I attached the PWM controller to the back of my dash and the dimmer knob to the bottom edge of the dash.
They're on the very lower right corner of this photo:

https://live.staticflickr.com/65535/51060502777_b6cc3f1714_b.jpg (https://flic.kr/p/2kN3qya)
Untitled (https://flic.kr/p/2kN3qya) by John Ibele (https://www.flickr.com/photos/familycobra/), on Flickr

You can see the dimmer knob in this photo:

https://live.staticflickr.com/65535/52443097035_a9965c77b0_b.jpg (https://flic.kr/p/2nUdzEc)
Untitled (https://flic.kr/p/2nUdzEc) by John Ibele (https://www.flickr.com/photos/familycobra/), on Flickr

Hope that helps.

[Papa]

You'll need something like this: https://www.amazon.com/ALOVECO-Interior-Ceiling-Recreational-Lighting/dp/B07Y2XC225/ref=sr_1_19?crid=2J7YDWVV9TSSI&keywords=LED+dimmer+12v&qid=1670298053&sprefix=led+dimmer+12v%2Caps%2C117&sr=8-19

[Jeff_J.]

awesome, Thanks guys.
Jeff_J.

[narly1]

There are things that help you "dim" an LED tho, such as PWM controllers that convert input voltage to a PWM signal that effectively switch the LEDs on and off really quickly to make them seem dimmed.
.

Thinking that it should be possible to home brew a circuit that converts the analog voltage out of the existing old school headlamp switch to PWM as required by the new LED illuminated gauges.

Earl

[edwardb]

FWIW, lots of forum bandwidth on gauge dimming. With 10+ years of driving various models and gauges, I've found (1) I don't drive at night nearly as much as with a DD, and (2) dimming the gauges just isn't a big issue. They're not that bright. I've had several versions of Speedhut and Autometer. I typically leave them on full brightness and rarely if ever change it. If the gauges don't dim out of the box, personally I wouldn't recommend spending a huge amount of time adding it. Likely you may never use it. Just my take.

[skidd]

I concur with Ed. Adding dimming to my SpeedHut gauges was a waste of time and money.

[rich grsc]

FWIW, lots of forum bandwidth on gauge dimming. With 10+ years of driving various models and gauges, I've found (1) I don't drive at night nearly as much as with a DD, and (2) dimming the gauges just isn't a big issue. They're not that bright. I've had several versions of Speedhut and Autometer. I typically leave them on full brightness and rarely if ever change it. If the gauges don't dim out of the box, personally I wouldn't recommend spending a huge amount of time adding it. Likely you may never use it. Just my take.
Make me another in agreement here. I have a dimmer, it came with my speedhut gauges, but don't think I've ever used it in 5 yrs

[Jeff Kleiner]

Add me to the don’t bother with a dimmer camp. As said, the backlighting isn’t very bright and even with a dimmer turned all the way down the gauge pointers stay at full intensity (except for the clock hands which don’t light at all…go figure out the thinking on that). Better to put your time and effort into something useful like utilizing the courtesy light function of the light switch for interior and trunk lighting.

Just one guy’s opinion ;)

Jeff

[Jeff_J.]

All good points.. Thx
Jeff_J.

[Ted G]

Make sure your switch is grounded. I mean the actual body of the switch. I have updated/custom gauges from Speedhut and I had the same problem because the body wasn't grounded by the carbon fiber dash. Ran a ground wire and now everything dims.

176539

[Nigel Allen]

I agree with the other posters that dimming is not needed, as the brightness level of these gauges is pretty much perfect.
However if you do wish to dim them using the rheostat on the headlight switch, you do not need to build a complicated circuit. What is missing from the current circuit is the load from all the incandescent globes that are normally installed in a dashboard. Without the load of the incandescent pilot lamps, there is no voltage drop across the rheostat when you adjust it to the low position. So the solution is to provide a dummy load, equivalent to the load of the original pilot lamps, between the output of the rheostat and ground. The dummy load needs to be a suitable resistor, nothing more.

Hope this makes sense. Reach out if you need any further support.

Cheers,

Nigel

[Theshandman]

Haven't driven at night yet (or for that matter much even in daylight) but when killing the garage lights at night and turning on the roadster lights, the gauge lights are not too bright to my taste. I wondered why the dimmer function of the headlight switch didn't change anything until I realized the dash lights were LED and thus didn't care about varying voltage, save for a specific on/on value.