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Courtesy light woes

1741 Views 12 Replies 4 Participants Last post by  PhillyGTV
I seem to be post happy, this Monday morning. The courtesy lights on my 71 GTV Euro have never worked. Fuse 1 immediately blows when an 8 amp fuse in put in. So my neighbor(an auto electrical engineer) and I tried to track down the short. We were using the wiring diagram supplied by papajam, titled 1750 GT Veloce Series 2. Here is what my neighbor said:

"Your door switches break the ground connection to the dome lamps.
The dome lamps however, are already grounded from the housing to the roof.
The dome lamps only have a single power lead from the fuse.
In order for the dome lamps to function with the existing door switches, there would have to be an extra wire for the ground. The ground wire from the lamps would go to the door switches."

Curiously enough, he happened to see a wiring diagram for a 1750 Berlina in my Autobook, that he said more resembles my car's courtesy light wiring.

Does any of this make sense to anyone? I am embarassingly inept at car electronics(my previous posts support that)!
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hey howieb4,
i don't have the schematics with me but for the 72-74gtv (115) the courtesy lights are a three way switch.
With the little lever In the middle the light never goes on.
With the little lever up (?or down) the light will go on (this is the circuit to ground at the light)
With the little lever down (?or up) the light will go on when the door is opened (this circuit the current flows thru bulb, light switch and thru door switch.

I would try removing both passenger and driver's side bulbs. If fuse blows there is a short before one of these two points (most likely).
If no short, try a bulb in one side only to determine if passenger or driver's side is causing the short. (i would suspect the short to be before bulb as if it was after the fuse probably would not be blowing as this is the normal circuit to ground).

I will also check when i get home to see what other components are utilizing the same fuse.

Best of Luck,
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Joe, the middle switch on my car only lights up the gauges. I think that's how it works in the 1750.
The dome lamps only have a single power lead from the fuse.
Looks like this may be a problem. All the light assemblies I recall ever seeing have two wires (like in the pic below) and function exactly as Joe describes. So perhaps your light has been modified at some point. Another possibility is that if Alfa did supply single wire courtesy lights, they were not intended for the 1750 GTV.


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the little switch i was refering to is part of the overhead interior courtesy lights.
this is true for both my 73 and 74 gtv's (don't have a 72 yet :)
i did find here at work a schematic for my 73.
3 fused lines coming off the #1 fuse are rear defroster (big black wire), key reminder buzzer and courtesy lights(red & black wires).
Your neighbor is correct if your wiring setup is as i described above, else logic would dictate that the current goes from the #1 fuse, through the (normally open ie switch/current path closes when door is open, switch is open when door is closed) door switch and upto and thru the lightbulb to ground.
Tracing this short is a little difficult as i believe you have to get under the carpet, headliner, side panels etc. to check the wires.
Most shorts are typically at connections or where a wire is subjected to repeated movements.
Also, and again this is from a 73 diagram, the hot red/black lead from #1 fuse goes first to driver's side cortesy light bulb, and from same side of bulb jumps over to passenger side bulb. (For both sides) the current can then go thru the bulb and to 1 of 3 places depending upon the position of the little arm/switch on the light itself:
1). to ground - light is always on;
2). to door switch (this would be the second wire your neighbor mentioned, it should be solid black) which when door is opened, switch is closed and current can flow to ground
3). No where as the little switch on the courtesy light creates an 'open' position. (lights will not come on when doors are opened)

At least i believe that is the way mine behave.

I will check to see if the 72 schematics and interior lights are different when I get home.

Anyone else care to pipe in here? Feel free to correct me.

Does your car have any other wires coming off the #1 fuse (same side of fuse as your courtesy light wires, not the other side)?
This is important to know to make sure some other circuit (defroster, key reminder...) is not the guilty culprit.

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Sorry Joe for the misunderstanding of the switch. My courtesy lights do not have their own switch. Of course I always pick up these posts here at work while my car sits at home, but if memory serves me right my light assembly is totally different than the photo that Jim posted. Mine has two depressions with some kind of serrated washer where the two beefy screws tie into the roof. There is also a spring loaded grab handle on it. I can't tell if in the photo that gold thingy on the left is the spring. I never took my assembly apart.
Joe, I forgot to answer one of your questions. According to my wiring diagram, Fuse 1 runs the courtesy lights, rear defroster, and cigarette lighter. And I believe we proved that to be correct for my car. If memory serves me, the cig lighter had more wires going to it than the diagram showed. I've copied my neighbor on all these posts, but I've yet to hear from him. He's probably running for the hills to get away from me!
Sorry Joe for the misunderstanding of the switch. My courtesy lights do not have their own switch.
After reading this post, it would appear that your grab handles may be inconsistant with the parts books listings and wiring diagrams. I'll check the books tonight but memory tells me that the door switches are a single wire affair meaning that they supply a ground, not power. For your lights to work with only one wire, the door switches would have to have two wires and be a normally closed (NC) switch isolated from ground.
The above pic is of the backside of the light assembly only to show the two wire connections (and the grab handle is not installed). The front of the above posted light is in the posted link and shows the two depressions.
Though it sounds as if others have pointed you in the right direction of your lights/switches not being made for the car, keep in mind that the wiring polarity of these little lights is important. When I had my car re-upholstered a few years back (and the head liner re-sprayed), the shop hooked one of the courtesy lights up with the wiring backward. This blew the fuse every time they were switched on, and kept my defroster from working (which is how I noticed the problem). I had to dig through the wiring diagram a while to understand why this mattered, and it took some time, but was a very simple fix. So check your wire colors carefully at each of the lamps, as it does matter!
thanks for finding the other thread. it sound like howieb4 might just have some lights from a gtjunior if they are only single wire. if this is the case i'd guess circuit runs from fuse 1 to door jamb switch, to and thru bulb, and ultimately to ground.
excellent point as this would cause a 'dead short' to ground right at the light.

Howieb4 (and any others who may one day stumble accross this thread) ,
as you mentioned your not the worlds greatest with electronics (me either)
just a quick note: make sure the battery Negative terminal is disconnected before you start poking arround the fuse box. my diagrams show the unfused side of 1, 2, 3, & 4 all being HOT to the battery. An accidental touch of that side to any piece of bare metal will definetely not be fun.
Also, in my last post i said it may be hard to find the short...
what i should have said is it may be hard to fix the short... for the previously mentioned reasons.
If you can safely disconnect the three leads (circuits) coming off the fused side of the 1 fuse, battery cable negative side disconnected, you can reconnect just one of the wires at a time to absolutely determine if the interior courtesy lights are causing the short.
And as JeffM recommended you could also try disconnected the wires at the lights themselves to see if the short is actually at one of the two.
With all three of your wires disconnected, and a cheapo volt meter (harbor freight $4.00) you could alternatively check the three wires independently to see if any of the circuits show a short to ground. If your neighbor hasn't left the state :) , he should be able to show you how to do this in about 1 minute.
Worst case scenario at this point you would have 2 of the 3 circuits you mentioned working just by reconnecting the wires back to fused side of fuse block.
With same voltmeter you can check 'continuity' to findout between which points the short is located.
Then its just a matter of how difficult or easy it is to replace / by pass the bad wire section. (or if you're really lucky JeffM was correct).

Let us know how you make out

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After an hours research, and sparing y'all the play by play, it would appear that howieb4's courtesy lights were originally fitted to a Berlina. I'll try to confirm (or deny) this...
Here's the proof!

Now that I am looking more closely at the light, I can see wear marks from the original light. So I guess now the question is can this be made to work or do I need to start to shop around for replacements! Any one wanna trade!

P.S. Again this board comes to the rescue. Now if you can only find a cure for global warming;)


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The plot thickens...
Sounds like if you get really lucky JeffM's advice might just work.

Have you unscrewed the lights to see if there is an extra set of connectors up there?

If there are, I would guess these lights would only work if the po had properly rewired the circuit to go through the dood jamb switch first, in which case i doubt you would be having the problem you have now. Or if there was some way they were wired in with another switch somewhere to control on/off.

If there are two connectors at each light, as originally wired, the simplest fix is probably to get the correct lights in place. And with a little quick testing you should be able to determine if the circuit is functioning properly, before you actually buy the lights.

Take JeffM's advice, disconnect the wires at both lights, don't let them touch any metal, and see if a new fuse blows as soon as you put it in.
You should also see at this point if you have two connectors or one at each light.

Jim, if i had perfect memory (not even close), maybe i could have remembered how my old berlina's lights worked - excellent detective work by the way - but back then i was really only concerned with how fast it went, how well it cornered and how easy it was to blow away the bmw 2002's :)

Howieb4, waiting for the next chapter.

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