instrument cluster light switch & panel light rheostat

7982X

7982X

So much fun it MUST be illegal!
InstrumentClusterLightSwitch.jpg On the 79....we have both the instrument cluster lighting switch (photo attached) & the panel light rheostat. In looking at the wiring diagrams, it appears that the instr. cluster switch is an OFF-LOW-HIGH function for the instrument cluster ONLY and the panel light rheostat is for the fiber optic unit & the cigarette lighter & the heater control panel ONLY. The 2 circuits are independent of each other. Is my understanding correct? Has anyone tried to run ALL of those lights through the rheostat? It seems silly to have both systems. Also, we could use the extra position on the console as we are adding an antenna switch & a factory fog light switch. Our 81 only has the rheostat.
Thanks!
 
on my 79 I wired around both (all lamps on full) and used all the switch locations for driving lights. (6 100W driving lights) My first ticket was 85 around 11:30 pm officer said normaly for those speeds at night He would wright wreckless driving for over driving the head lights, But He was sure I had enough light infront of Me to stop in time if I saw something.
 
I think both the switch and rheostat are a waste as the lamps are not that bright anyway. I always had them both turned up all the way and the lights were still dim. I modified the instrument panel switch to be a double pole switch. One pole is a kill switch and the other pole activates the relay for the radiator fan. When the switch is off, no start. In the middle or top start. The fan only comes on with the switch at the top position. The kill switch controls the relay for the fuel pump.
 
However if you convert to LED's for the entire dash, then they are too bright and a 'dimmer' control is necessary. I recall Bob Brown explaining there are two types of rheostat dimmers on X's. One type works to dim LED's, the other does not. Anyone recall which is which? Or better yet, which years will work to dim LED's?

This still leaves the original question though; can they all be tied together through the dimmer control? I would think so, but I'll defer the definitive answer to one of our electrical experts.
 
The dimmer in my 87 does not work with leds. I removed them from the B.B. cluster as a result & went back to incandescent. I stayed with incandescent for my modified tach position cluster.
 
Dr. Jeff, it does make you scratch your head, doesn't it?
After posting this, I went back & did some checking & it looks like 79-82 uses the same rheostat, so it should work to bypass the switch & just run everything through the rheostat (like the 81 is wired). Another thing that we discovered (although everybody else here probably already knows this) is that the instrument & panel lights come on with the key in the ON position, not with the light switch (parking or headlights on). I don't think that I ever noticed that before. It seems a waste to have the instrument & panel lights on in the daytime, when you don't have your parking/headlights on. We may reroute the wiring to have the instrument & panel lights come on only when the outside lights are on (like our other vehicles). Also, we will likely bypass the instrument light switch and may also bypass the rheostat and have them at full brightness as I can use all the light I can get at night. We did convert our interior lights to LEDs. It seems to look good on the bench, but the proof will be when it is installed in the car.
We may also use Rodger's idea of putting a fan switch (for our second radiator fan) in the console. (We are using a VW radiator switch to run the two fans normally, but could use the console switch as a manual bypass for the second fan). The kill switch position is a clever idea as well, but will think about that.
By the way, Rod, do you have a couple of extra batteries in the frunk to drive those driving lights? 6 100W lights? WOW!
Hussein, didn't you do the instrument cluster with the LED strips inside the housing?
As always, your input IS appreciated. I couldn't come up with half of these ideas myself!
 
Funny, I've never noticed if the instrument lights come on with the key switch. Frankly I don't drive the X much, and really almost never at night. But agree that is a stupid design. If you figure out how to rewire it to the headlight switch, please tell me how. Same with how to bypass the dash switch for the other interior lights; I'd also like to put everything through the rheostat. Keeping the rheostat would be good if you have LED's (they are VERY bright, too bright for my preference), assuming the type of rheostat is the one that will work with LED's.

Huss, thanks for the feedback on your '87 rheostat and LED's. I wonder what other years are the same as yours? And which years do work with LED's.

Regarding rad fans. This has been discussed before, personally I don't see the need for a manual switch to control them. But I understand others do. Since you are running two fans (great idea), one option is to run the VW rad switch with 3 poles. It is a dual temp switch. That allows one fan to come on at the first temp level, and the second to also come on when the second temp level is reached. Saves on the charging circuit load, less noise, and a smoother control of the coolant temp. On the same topic, the VW switches are also available with various temp settings; cooler than stock is a good idea if you run a cooler than stock thermostat (both are excellent ideas in my opinion).
 
The rheostat in the 81 (which I think is the same for 79-82) works to dim the LED that we put in the fiber optic light source socket. We haven't changed that instrument cluster to LEDs yet.
The VW fan switch is to be installed, functioning as you suggested, turning each fan on at a different temp. The manual switch is to be used as a backup in case the VW switch fails and as a "judgment call" option, such as anticipation of slow moving traffic in 90 degree weather, etc.
 
If you've converted your cluster to LED's, AND you have an electronic dimmer, you can add the dimmer control to the back lighting lamps within the cluster by doing the following:
Attach a piggyback spade connector (male/female combo) to a 3 foot yellow/red stripe wire and attach one end to the lamp behind the console that controls the Fiber Optic lamp. (there should be a spade connection that plugs into the back of the lamp socket and this connection basically taps into this wire) Run the other end to the gauge cluster and attach it to the RED connector marked "Gauge Backlighting +" (middle pin, closest to speedo) You only need this one wire to do the trick. Obviously, you will first need to remove the existing connection to this pin on the red connector block. (a paperclip will bend in the female spade locking tab) Tape or heat-shrink the original connector/wire so that it doesn't short to the chassis or other connections. Wouldn't hurt to identify the removed wire for future owners. :)

Important: If you perform this mod before changing the lamps to LED's, you will burn out your dimmer in short order. The dimmer can't handle the current draw of incandescent lamps.

-> Cluster pinout here <-
 
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I believe all X's after 1976 and beyond have the electric dimmer, but I'm not positive.
Easy to identify, as the electric dimmers all have little circuit boards with components on them.
The resistive style had thin layer PCB with no components. Only wire traces.
 
Thanks Bob, excellent information. If you happen to have a photo of each type handy, that would be helpful for others. ;)
 
Dimmers,01.jpg

Dimmers,02.jpg

Here are photos of 2 dimmers that we have. I didn't pull the resistive unit apart as it looks a bit more difficult to do without damaging it. The electronic unit came out of our 81 as the terminals appeared to be intermittent (will have to check the solder joints). One of the resistive units came out of our 79 and the other resistive unit came out of another car that we parted out over the years....not sure of the year.
Per Bob's suggestion, the plan is to add the wire from the fiber optic bulb to the instrument cluster, so that the dimmer will control both. Then, we will replace the red wire feeding +12v to the dimmer with a red wire from the dimmer to the "downstream" side of fuse H or G to supply +12v to the dimmer only when the lights are turned on. It doesn't make sense to me to have the panel & instrument cluster backlighting on unless the lights are on. (These are the only cars that we have had that have these lights on any time the ignition is on.) We will probably use the same color wires that we are replacing, as we have a harness that was removed from the 82 that we parted out and have those wire colors available. I will still need to confirm that the resistive dimmer will dim the LEDs.
 
The resistive dimmer will not dim the LEDs. Not enough current draw on the LEDs for that to happen. Thanks for the photos BTW.
 
Thank you for the pics, very easy to see the difference now.
Off hand I don't recall. Are the two types an interchangeable fit physically? Meaning can one type be inserted into the same hole on the control panel as the other type? Or are the two different dimensions? Seem to remember they are different sizes but not certain.

And thanks again Bob for the technical info, very helpful.
 
"The resistive dimmer will not dim the LEDs. Not enough current draw on the LEDs for that to happen. Thanks for the photos BTW."
Thanks for the insight....It never occurred to me that the current draw would be an issue here. If you placed a resistor in parallel with the rheostat to lower overall resistance, might that work? Just a thought.

Are the two types an interchangeable fit physically?
They sure appear to be the same, although I am having some difficulty getting it all the way into the console panel in the 79. I think the problem is the "springy" devices on the top & bottom of the electronic rheostat unit seem very stiff when compared to the resistive units. If I can resolve that issue, I think it will fit. The faceplate fits when you put the face into the panel from the front side.
In looking at some much later X1/9s, it appears that they have a dimmer that looks very different from the ones we have. They do not look like they would even come close to fitting in the 79-82 panels.
 
7982X said:
"The resistive dimmer will not dim the LEDs. Not enough current draw on the LEDs for that to happen. Thanks for the photos BTW."
Thanks for the insight....It never occurred to me that the current draw would be an issue here. If you placed a resistor in parallel with the rheostat to lower overall resistance, might that work? Just a thought.

Are the two types an interchangeable fit physically?
They sure appear to be the same, although I am having some difficulty getting it all the way into the console panel in the 79. I think the problem is the "springy" devices on the top & bottom of the electronic rheostat unit seem very stiff when compared to the resistive units. If I can resolve that issue, I think it will fit. The faceplate fits when you put the face into the panel from the front side.
In looking at some much later X1/9s, it appears that they have a dimmer that looks very different from the ones we have. They do not look like they would even come close to fitting in the 79-82 panels.
Click to expand...
Denny:

A resistor in parallel would make matters worse. What you need is a higher value rheostat. If you are locked into that rheostat for mechanical reasons you may be able to scale down the current range using a voltage divider or current mirror depending on how things are wired. Probably won't save much power though. Does anyone have info on the rheostat? Depending on how it is built, you might be able to exchange the guts for a higher value. If you want maximum efficiency, you could go to pulse width modulation with a simple circuit and if you got lucky, perhaps you could control it with the existing rheostat.

Don
 
Don has addressed this better than I could, so this is just an added thought. While I get the logic of adding resistance to LED's, like is done to make the 'flasher' work correctly, it does not seem like a good solution to me. One of the great benefits to going to LED's is their low current draw. Adding a resister just negates that advantage. Especially on the X where the wiring system is over loaded already.

Please keep us informed on how it goes with installing the 'electronic' rheostat into your '79. Especially in light of what Don just said, it seems much better to use the electronic unit in those cars that came with the 'resistive' type.

Interesting that there is yet another type in the later X's (I guess 3 versions in total). I know those models have many little changes (for example the headlight switch) so no real surprise. I wonder what year this changed for the dimmer control.
 
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