Headlight switch, headlight pods, and related circuits

Dr.Jeff

Dr.Jeff

True Classic
I've been going through my '79 X's electrical system as part of the complete restoration/customization projects. One circuit I still can't quite figure out is how the headlight switch, the high/low switch, the changeover relay to the pods, the relays for the pod motors and other related components are wired. It's my understanding the '79 is unique in several aspects of this particular circuit. Therefore many of the threads relating to aspects of the lighting circuit do not pertain to the '79. Some of it makes sense but not everything.

I have the '79-only wire diagrams and have physically traced every wire from its source to its destination but I'm still not clear how the changeover relay ("lighting relay" according to Fiat) interacts with the "up/down" contacts on the pod motors, the relays to those motors, and the headlight and steering column stalk switches. It appears power comes through the headlight and column switches to the changeover relay, and then to the two up and down pod circuits, but somehow also to the parking/side marker lights and headlight relays (I realize that isn't possible but that's how it looks).

Some of the components involved include fuses "G and H" for most of the outside lights, fuses "I and L" for the headlight motor relays, as well as fuses "Q and R" for the up and down functions of the pods. As noted the main headlight switch and the steering column "high/low beam" switch are also in the circuit. Plus there's also lots of other things like the switch for the cluster lights with its resistors, the dimmer rheostat, the ignition switch, the clock, warning lights on the instrument cluster, fuses "A and B" (all of the 'switched' circuits), etc, that are tied into all of this. But for the most part all I'm really interested in is how the "lighting (changeover) relay", headlight switch, and the outside lights interact.

Can anyone please "enlighten" me with "illuminating" knowledge on this.
 
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I believe you are confusing powering the objects with providing a controlling signal. In the case of the relays the thing they are powering gets a power source through a fused circuit which is not going through the switch. So while the signal power to the relay comes from and goes through the lighting switch the actual power to run the motors does not.
 
kmead said:
I believe you are confusing powering the objects with providing a controlling signal. In the case of the relays the thing they are powering gets a power source through a fused circuit which is not going through the switch. So while the signal power to the relay comes from and goes through the lighting switch the actual power to run the motors does not.
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Actually quite the opposite. This particular circuit is not configured in a conventional way as we would expect. For the change-over relay it appears possibly Fiat did exactly the opposite of normal and ran the power source for it in reverse so to speak; there are two possible power sources that are selected between when the relay is switched over and then fed to a single destination. As opposed to the other way around - one power source that is switched to two possible destinations. I think. But it also appears that relay serves to trigger two others, on different circuits, in addition to controlling the first function separately at the same time. On one of those circuits the power (not signal) is then fed through the headlight switch. I think. The '79 headlight switch is unique and functions differently from the others, in a very bizarre way. There have been discussions just trying to figure out why the headlights seem to be operating wrong, when in fact that is how they were designed to work.

Later I'll try to cut and paste some illustrations from the wire diagrams to show what I'm talking about.
 
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I can't figure out how to reproduce the pages here, so look at the Wiki in the "Electrical System", under the "Wire Diagrams" section, for the "1979" model [https://xwebforums.com/wiki/images/a/a4/1979_wiring_diagram.pdf]. Pages 2 and 3 specifically show the components I'm asking about. You kind of have to meld those two pages together because neither of them tell the whole story.

Starting on page 3 you will see the "lighting relay" toward the top of the page. Tracing the wires from it you find fuses G/H and Q/R are involved. The see where those fuses lead refer to page 2. The headlight switch is on both pages but showing different wires to it, for different functions. This is one of the aspects of these diagrams I hate, you never get the full picture. Between the two pages you can also see how other components are involved, like the high/low beam switch, ignition switch, left and right headlight relays, the pod motors, the instrument cluster lighting switch, etc.

One particular area of confusion is the "yellow" wire coming off of terminal 30 of the "lighting relay" (page 3). It feeds power to fuses G and H, which power the outside lights. But if you look inside the lighting relay, terminal 30 is switched between terminals 87 and 87a, depending on the signal to the relay coil (it is a changeover relay). Therefore it appears the power source that is being fed through the yellow wire will come from one of two possible sources (87 or 87a). However if you trace the "light blue" and "light blue/red" wires from those two terminals they lead to the headlight pods "up and down" function switches on the headlight motors (see page 2, the grey/yellow and green/white wires). This makes no sense to me. How are the outside lights and the pod up/down functions related? And how does the current travel through the lighting relay?
 
I think I've figured out some of this puzzle. Specifically regarding the "lighting relay", a changeover relay that does multiple functions.

Power from the key switch energizes the relay when the key is "on". That positions the changeover connection between terminals 30 and 87. Terminal 87 brings power from the headlight switch, depending upon its position (I still haven't figured out exactly how the headlight switch works). The power is transferred to terminal 30 which goes to most of the outside lights (parking/running lights, etc).

At the same time, this configuration of the key switch and headlight switch also powers fuse "R" - which triggers the headlight pod relay to open the pods.

Turn the key off and the lighting relay is no longer energized, switching the changeover to connect terminals 30 and 87a. Terminal 87a brings power from the headlight light switch when it is in another position from above (again, not sure of the various headlight switch positions). The power is again transferred to the outside lights, depending on this position of the headlight switch.

At the same time, the same configuration also powers fuse "Q" - which triggers the headlight pod relay to close the pods.

Change the position of the headlight switch and all of this changes again. This odd configuration is why the running lights will only go on if the key if off or the headlights are on. See this thread for more on how that arrangement works:

1979 x1/9 (US), headlight/marker/"parking" light operation - what's "correct"?

As I'm about to add various circuit improvements (relays, BWM, uncovering the dash backlight switch & hazard switch previously buried behind a custom center console by the PO, reviving some switch backlighting, etc.) on my 1979 X1/9, I've found myself slightly baffled by the light switch...
xwebforums.com

So my earlier assumption that the power circuit runs through the lighting (changeover) relay in the opposite direction of conventional was correct. I was also correct in guessing that the key switch, lighting relay, outside lights, headlight switch, high/low beam switch, and other components all interact in a bizarre non-logical way. However I still haven't figured out how the '79 specific headlight switch functions. So I'm still at a roadblock for my custom wiring changes.

I think the lighting relay can be eliminated and the power to the running lights can go directly from the headlight switch, like every other car in existence. It looks like this will not affect the function of the headlight pods going up and down, as the lighting relay doesn't seem to play a role in that. These changes should also eliminate the funky operation of the '79s running lights, as described in the thread linked above.


EDIT: After posting this I re-read the linked thread discussing how the pods function (see link above). That helped to clarify how the position of the headlight switch interacts with the pods and running lights, at least in function if not in wiring. So some of my earlier comments about how the headlight switch works are no longer as much of an issue and I think I can proceed with my wiring mods by completely eliminating the "lighting relay".
 
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Removed the "lighting relay" and all of its associated components. As should be expected there were surprises. The schematics do not show a wire connection that directly links the relay to the high/low beam switch on the steering column, in addition to all of the other connections I've already discussed. But it is there. Actually it's another of those very long wires that goes all the way over to the opposite side of the car then back again before ending right next to where it started. So I had to work around that, but it wasn't too difficult....just cut out more wires. :D
 
I believe I've determined the basic wiring for the '79 headlight switch. For as many circuits and functions it affects, there isn't that much to it....just a very odd way of doing it.

First the wires/terminals on the switch:
"H" = blank.
"L" = white wire. Goes to a few things but basically is a constant power source (i.e. not through the key switch, but always hot).
"V" = light blue wire. Goes to one side of the changeover ("lighting") relay, as well as fuse "Q" (triggers the pods to go down).
"T" = brown wire. This is just jumpered to "U"...see next.
"U" = black wire. Goes to the key switch for a "switched" (i.e. only hot when key is on) power supply.
"I" = green wire. Goes to the other side of the changeover ("lighting") relay - opposite "V", and to the high/low beam switch on the steering column, and to fuse "R" (triggers the pods to go up).
"D" = blank.
"CAVIS" = blank.

When the headlight switch is in position 1 ("off"), it isn't really off, but "V" and "T" are connected. This provides a power signal to trigger the pods to go down, and it routes power through one side of the lighting relay to power the external lights (running/parking lights). Although the 'parking' lights do not go on while the light switch is off, but the key is on. So I guess "V" is only connected to lower the pods in this configuration.

When the headlight switch is in position 2 ("parking lights"), "V" is connected to "L". This provides a signal to trigger the pods down, and routes power to the same side of the lighting relay (without raising the pods). That allows the parking lights to be left on when the key is off, a throwback to the old days of Europe when cars were left parked half way in the street.

When the headlight switch is in position 3 ("lights on"), "U" is connected to "I". This provides power (through the key switch) to the high/low beam switch - which in turn provides power to the headlights. It also provides a signal to trigger the pods up, and it powers the lighting relay to turn on the running lights.

Again I'll refer back to another thread that describes the weird lighting functions on the '79 to help explain all of these settings:

1979 x1/9 (US), headlight/marker/"parking" light operation - what's "correct"?

As I'm about to add various circuit improvements (relays, BWM, uncovering the dash backlight switch & hazard switch previously buried behind a custom center console by the PO, reviving some switch backlighting, etc.) on my 1979 X1/9, I've found myself slightly baffled by the light switch...
xwebforums.com

All of this can be grossly simplified by eliminating most of it and using a double throw "ON-OFF-ON" (or "A/B") toggle switch. The middle terminal would have switched power, the "A" side would be to the running lights, and the "B" side would be to all of the lights. When the switch is in the middle ("off") it also triggers the pods down. When the switch is on "A" it turns on only the running lights, pods still down. And when on "B" it turns on all lights and triggers the pods up. Only a couple of wires and a simple switch are needed to do the same as the original system.
 
This has already been sorted out.
See: Headlight Pod Description and Alternate Headlight Switch. With the details contained in these documents, you should have everything you need to understand the function of the X1/9 headlight electrical system.
Contrary to popular belief, the headlight switch function is exactly the same on ALL X1/9 models, sans the switch itself. The older model X uses a different toggle switch whereas the later model uses a slide switch. The wire colors are pretty-much the same, thought I've seen different shades on the wire colors. FYI the hotlinks above are PDF document downloads so you can have them on file whenever you need them.
Enjoy.
 
bbrown said:
This has already been sorted out.
See: Headlight Pod Description and Alternate Headlight Switch. With the details contained in these documents, you should have everything you need to understand the function of the X1/9 headlight electrical system.
Contrary to popular belief, the headlight switch function is exactly the same on ALL X1/9 models, sans the switch itself. The older model X uses a different toggle switch whereas the later model uses a slide switch. The wire colors are pretty-much the same, thought I've seen different shades on the wire colors. FYI the hotlinks above are PDF document downloads so you can have them on file whenever you need them.
Enjoy.
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I certainly won't argue with you, but having reviewed those documents (and others) several times before I am convinced the '79 is different. When I tried to apply the info found in those docs to my system it did not match up and I wasn't able to sort out how things worked. Granted most of it is the same or very similar, but there are enough differences to throw things off - at least for a simple mind like mine. :D
 
bbrown said:
This has already been sorted out.
See: Headlight Pod Description and Alternate Headlight Switch. With the details contained in these documents, you should have everything you need to understand the function of the X1/9 headlight electrical system.
Contrary to popular belief, the headlight switch function is exactly the same on ALL X1/9 models, sans the switch itself. The older model X uses a different toggle switch whereas the later model uses a slide switch. The wire colors are pretty-much the same, thought I've seen different shades on the wire colors. FYI the hotlinks above are PDF document downloads so you can have them on file whenever you need them.
Enjoy.
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Perhaps your resources can help me with a remaining question. The way the changeover ("lighting") relay is wired, it will either power the running lights when the key switch is on or off, but from different power sources (constant vs switched), also depending on the position of the headlight switch. From the looks of it, with the headlight switch off (V connected to T), and the key on (lighting relay powering the lights from the key), the running lights will be on. Obviously that can't be, the running lights aren't always on when the key is on. Did you find something different there? Thanks.
 
The headlight relay location for late models controls power to the filaments (in red) but (unfortunately) I don't have the layout handy to the early model relay cluster that identifies which relay that is. Hopefully someone here can identify it.

Headlight Relay identifier.png
 
bbrown said:
The headlight relay location for late models controls power to the filaments (in red) but (unfortunately) I don't have the layout handy to the early model relay cluster that identifies which relay that is. Hopefully someone here can identify it.

View attachment 50682
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You can find the location of the '79s changeover "lighting" relay in the documents I linked earlier (unfortunately I can't reproduce it here). That also shows the '79s wiring schematics. But the location of the relay wasn't the question. The way it is wired to the other components and how it functions relative to those components is what's different about the '79 compared to my newer X's. And it isn't designed in an intuitive way - at least not to me. :)
 
HI everyone , I,am having headlight problem ,when switch is in second position parks are on ,when going to third position parks go out and lights do not go up ,if I jump white to green lights go up and parks are on , if I bring power to single brown wire on switch they will also go up , when putting switch to off lights go down and off , and another twist had car running to flush cooling system and went to try lights nothing on second position and in third all worked ,did this twice problem changes ??
 
Irregular electrical behavior like that might be due to poor connections. Possibly at any of the numerous grounds, wire harness connectors, fuse panel connections, etc.
 
Dr.Jeff said:
Irregular electrical behavior like that might be due to poor connections. Possibly at any of the numerous grounds, wire harness connectors, fuse panel connections, etc.
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HI JEFF I have been checking connections ,fuses ,relays , do you know the motor relay wiring specs , I seem to have no power there , should be power on one and power on another with key I think ,
 
This whole headlight system is very oddly designed, especially on some years. For example a '79 (which I believe you have) has a unique layout due to still having the old style headlight switch (complete 💩 in my opinion), the fuse box is partially old style and partly new, and the operation tried to maintain the Euro habit of being able to leave your marker lights on when parked with the engine off, but also tried to offer some more modern functions. Earlier in this thread it was stated they are all the same, however I eventually realized that is definitely not true...there are significant differences for certain years. Trying to sort that '79 wiring harness is a nightmare, as you can tell from my earlier posts.

On the '79 (again, I believe that's what you have) there are two relays labeled as "headlight". But they are not for the lights. And they are not regular relays. They are "changeover" relays for the motors that operate the pods (headlight buckets). They work in conjunction with switches and diodes on the motor drives (one on each headlight pod). And they are controlled by the headlight switch as well as the steering column lever switch. Even the emergency flasher switch (as well as the flasher itself) is involved.

Therefore those relays won't operate as you might expect in terms of when power is applied and where it goes. To be honest it took me several days to fully figure out this whole system on my '79. And to be more honest I'm not sure I can explain it very well now (it was all a bit fuzzy to me at best). Hopefully my prior post (#7 above) will help some in trying to diagnose your issues. Also review the thread linked in that post to understand how it should function in general.

A couple thoughts to consider. When you flushed the cooling system water might have splashed onto the headlight motors and their switch housings. If they are not sealed this may have caused a short and triggered a different behavior than you experienced before. Hince the changing nature of things. Also like I said, a dirty or loose ground can cause intermittent behavior. There are several grounding locations (those metal "spider" things), including one by each headlight motor area, one on the driver's side under the dash, and others elsewhere (likely not related to the headlights). Those are notorious for having issues. Also check all of the "spade" terminals (the 1/4" flat push-on connections) for all of the related wires. There are several of them at the fuse panel, the relay panel, the headlights, the headlight, steering column and emergency switches, and elsewhere. They tend to get loose or corrode. Even the fuse prongs get bent or corroded and loose good contact with the fuses. So cleaning and tightening them (with new fuses) can resolve many issues. From what you said I don't think it is a diode issue (at the motors), but the switch contacts inside those housings could be dirty. And look for bad wires; it is common for the insulation to wear or rot away exposing bare wire, or the wire itself corroding away.

Frankly there is a multitude of things to check, test, clean, tighten, and sort out. I wish I could short track it for you by saying exactly where to look, but I can't. I just started going through things one by one; and mine was actually functioning correctly to begin with, I started out wanting to do some general maintenance and began to discover a long list of little issues everywhere. Electrical systems were certainly not one of Fiat's strong suits.
 
Further thought. Do you have the unique wire schematics specifically for the '79? They are available in the Wiki:

Unfortunately there are a couple of errors on them, but not too many. And each schematic only shows the wires and components directly related to the particular circuit. However there is a LOT of overlap between them. So you kind of need to look at more than one at a time to follow things.
 
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