Dash Cluster Illumination

Dano944 · 09-06-2023, 12:50 PM

The illumination in my dash cluster on my ‘83 944 is very dim. I have rarely drive my car at night, so I can’t honestly say whether this just happened or if this is the way it’s always been. And yes, the illumination dial is turned up all the way. Is it a bulb or could there be another issue besides a bulb? And if it is a bulb, does the dash cluster need to be removed to replace?

Monkey Wrench · Monkey Wrench's Garage

if there is a dash lights dimmer , I think the thing there is the dimmer isn't handling many amps so it takes very little resistance to make a change in brightness. its a variable resistor in series with those very low amp bulbs so there is very little current so it doesn't take very much resistance, some dust in that dashpot is likely the issue. maybe try a spray cleaner?

I think every car I ever owned had this issue. you can always jump that resistor and just have them at full brightness. I can't remember ever being bothered by them being too bright. i often end up waiting for a street light to light up my dash to see how much gas I have.

if you get them working you can see paradise by the dashboard lights ;-)

https://www.youtube.com/watch?v=a136H5K3OKw&ab_channel=MeatLoaf-Topic

Dano944 · 09-06-2023, 03:20 PM

[QUOTE=Monkey Wrench;12083702]if there is a dash lights dimmer , I think the thing there is the dimmer isn't handling many amps so it takes very little resistance to make a change in brightness. its a variable resistor in series with those very low amp bulbs so there is very little current so it doesn't take very much resistance, some dust in that dashpot is likely the issue. maybe try a spray cleaner?

By “dash light dimmer”, do you mean the in-dash dial that adjusts the brightness? If so, does that involve removing the gauges panel? If so I’ll Leave that to a shop, as I’ll break stuff if I do that🤣

924RACR · 09-07-2023, 03:55 AM

For sure, cleaning the dimmer switch is a good start... but I'd expect them to still be dim.

You can upgrade to a brighter Euro-spec bulb, found those once upon a time, that at least made them legible. But still not awesome.

I finally went to LEDs in my 931 (same dash)... and it's wonderfully bright and modern as well. There's a good thread over on Rennlist on this, hell I may have started it, I forget...

All options require gauge cluster removal, except the dimmer switch.

curtisr · curtisr's Garage

Quote:

Originally Posted by 924RACR

There's a good thread over on Rennlist on this, hell I may have started it, I forget...

Might this be it? Late 944 Dash LEDs...a reference post

walfreyydo · walfreyydo's Garage

Recommend upgrading to LED bulbs - this clarks article uses incandesent bulbs (outdated). Also recommend some of that double sided metal insulation tape - works well for the reflectors (your issue is likely due to the reflectors being old and no longer shiny).

https://www.clarks-garage.com/shop-manual/elect-08.htm

I also went with LEDs and updated the reflectors and the dash is very very well illuminated now.

PS - there should be nothing stopping you from removing the gauge panel - its very easy to access...

Monkey Wrench · Monkey Wrench's Garage

I made the mental comparison between the brightness adjustment for the instrument cluster and a vlume control on one of those older 9 volt transistor radios.

with such radios it was very common to have a crackly volume control and similar happens with the brightness adjustment.

what I think is happening is that there is a very small (amp) load in either case, sine the load is small so is the variable resistor is very sensitive.

because the variable resistor is so light duty, it is then very susceptible to things like dust and corrosion between the wiper and the resistor. the adjustment seems ot have a bit of a slightly bumpy feel to it so without disassembling it to see I'm imagining a wiper and a wound up resistance wire is used and since it isn't used often the wiper and resistor may become somewhat dirty, corroded etc and then the next thign is no contact. there is not a very high amp load so the current doesn't have the power to "blow through" the dust or corrosion.

I think if it had a higher amp load it would be less sensitive to this.

in a similar way if you think back to the days when you owned a 9 V transistor radio you would often find if it sat then the volume control would become scratchy and unreliable , for the same basic reason.

so then people want a brighter display and read they can get more lumens with the same voltage, yes you can, but the inherent problem with LED's is they have even lass power draw.

my theory is that by reducing the load , the variable resistor will become almost useless or may be unreliable because it isnt' seeing enough load to work right.

Some of those LED's may have a resistor to increase the load to similar to the original and that may fix this issue.

in my volvo my dash light went out and I went to an auto parts place and he opened up the drawer he had and said go ahead pick one ..
I found one that was about the right size but the little connector wires were stainless steel. I know I can;t solder to stainless.
what I did was wrapped many turns of fine wire around those stainless steel wires and soldered them anyway, the solder of course can't stick to stainless wire, but because they had lots of wraps I still got a good connection then I had something I could solder to. that was my workaround.

the variable resistor is in series with the load, it provides a voltage drop in the circuit but hat voltage drop is dependent on the load of the bulbs which are in series. If the load is reduced it will require an even smaller resistance to divide the load appropriately. If you had great big bulbs that variable resistor could be increased in its ohm rating..

i thin if one wanted to they may short the adjustment then there would be no voltage drop through it or one could use a fixed resistor to lower the intensity to a brightness they liked, a switch could be added to have a high or low brightness, a fixed resistor wont be susceptible to this dust and corrosion issue.

cleaning the variable resistor with deoxit might help if you can get some spray inside the switch and work it back and forth a bunch of times to clean it.

personally Id keep it original and clean the swithc and replace any burned out incandescent bulbs with incandescents theat have a similar resistance or if using LED's wire an appropriate fixed resistor in.

if you know the resistance you can calculate the resistance required to reduce the voltage, what I'd do there is just set them up on a temporary "test bed" and swap in some resistors from an assortment and see what happens

if you want to do the math it's basically ohms law. V=Ix R , voltage equals current in amps times the resistance. you know it's 12 V, the resistance may be on the packaging the bulbs come in. at no resistance the voltage across he bulb is is 12 increasing the resistance will dim the bulb as it will receive less voltage across it because it is in series and sharing it's load with the resistor..

the resistor provides a voltage drop in the series circuit from the battery through the dimmer and to battery ground. as you increase the resistence the voltage drop becomes greater so instead of 12 V acros the bulbs it is less, perhaps 8 volts.

the resistance may vary as the intensity changes. so there the math becomes beyond me so I'd just experiment with some different resistors.

if the bulbs were providing 1 ohm of resistance and the variable resistor was 1 ohm then the voltage across the bulbs would be 6 volts, the bulbs and the resistor would be sharing the load evenly.

if you go stick in bulbs with a lower amp load , lets say they are .1 amps then you have a

The math may be confusing but the voltage will always add up to 12 and I think it's easier to just think in terms of the voltage drop. someone good at math can use the resistance and power draw in amps to calculate the appropriate power range.. Personally Id just try experimenting with them out of the car.

I think what you may find happen with the LED's is that they don't dim but when they reach a certain voltage across them they just come on. a incandescent will burn down to a very low brightness at a low voltage but the LED is a different animal, I think it will stay on until the voltage is too low and then just go out.. so as result of that, using LED bulbs might make the dimmer not work at all?

I just replaced a 115 V incandescent at home with an LED bulb and noticed on the packaging it said non dimmable. I assume this is why.

if you set this up on a test bed you can just take your meter and measure the voltage before and after the resistor or across the bulb and get a voltage reading.
If that dimmer switch isn't too hard to get to Id try cleaning it if the problem is not that the bulbs are out , just that the variable resistor has so much resistance due to dirt and dust that the lamps wont shine brightly. If I wanted a simple fix I'd just short the leads of the potentiometer providing no adjustment but the lamps will then burn at full intensity.

so far as the load on the charging system the amperage is so negligible I dont think it's really a factor worth bothering with . If one prefers the whiter light of an LED to the original bulb than that's a reason to change it. Personally not something I care much about. i just wan to be able to read the guages.

Im in the city so I never have issue with the too bright , its these new cars with super bright headlights that bug me. maybe if you do a lot of highway driving out of the city its a factor for you.

I was going on to think that during remote highway driving one might have their high beams on and it might be possible to rig things so when high beams are on the dash lights are dimmed. that may not be practical, just a thought.

I dont think the OP ( Dano) cares about them being LED, they might just have a dirty dimmer so Id' suggest that if they can get the switch out , can try to spray deoxit in there and work it back and forth 50 times.. and see. failing that I'd suggest just putting a jumper wire between the two spade connectors so it has no resistance and maybe if Dano has just full intensity it may save paying a shop mechanic for just doing that job..
I dont expect the OP will understand about voltage drops through the circuit. and ohms law calculations, but maybe .. I think converting to LEDs is a bit much for what the OP really needs to accomplish. If the bulbs are burned out then yea the dash needs to come apart and it may be too much and that may be some shop time and maybe a couple hundred bucks for a mechanic to change a light bulb.

if you unhook the wires and put a meter on ohms across the two terminals then turn it you should be able to see the resistance changing or you may see that the control is intermittent.