Right blinker doesn't work if headlights are on???

petex19

petex19

True Classic
Restoring my son's '74X and getting it ready for safety inspection is coming along great except for one puzzling issue...

The blinkers work correctly until the headlights are turned on and then the right blinker doesn't work at all. The left works with lights on or off but not the right?

Any suggestions at all would be great,:help:

'PeteX1/9
 
Yep

Turn signal ground is bad, grounding through headlight or parking light instead, which doesn't work when the light providing the ground is on.
 
This may be a stupid question and I will check around both headlight buckets but is there a specific relay for right and one for left marker lights because like I mentioned, both blinkers work but once the headlights are turned on then for some reason the right blinker doesn't work anymore?

'PeteX1/9
 
petex19 said:
This may be a stupid question and I will check around both headlight buckets but is there a specific relay for right and one for left marker lights because like I mentioned, both blinkers work but once the headlights are turned on then for some reason the right blinker doesn't work anymore?

'PeteX1/9
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On a '74 - there's one blinker relay only, under the dash. It's flashy output is routed through the turn signal switch to the appropriate side blinker light. Problems in that circuitry would either kill both lights or not be affected by the headlights.

Almost certainly the problem is in the ground for the right blinker; you can verify this by pulling the connector at the lamp, put a voltmeter lead on the blue wire (assuming the wire colors are standard, a not always safe assumption with the older cars) and the other lead on a known-good ground, see if a pulsing +12 is getting there. I'm betting that it is.
 
Is "the connector at the lamp" referring to the positive lead at the right blinker? So on my voltmeter I would be checking VDC I'm guessing. Trying to understand all of this are you suggesting that the ground coming from the blinker itself is bad or a different ground?

'PeteX1/9
 
petex19 said:
Is "the connector at the lamp" referring to the positive lead at the right blinker?
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yes. The question you'll be answering is whether electricity is making it that far.
So on my voltmeter I would be checking VDC I'm guessing.
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Yes. The voltage will needle will alternate between zero and 12 because its driving a flashing light. You can double-check by doing the same thing at your working light, so you'll know what "good at the connector" looks like.

Trying to understand all of this are you suggesting that the ground coming from the blinker itself is bad or a different ground?
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It's the same suggestion that Steve and Greg have already made. The most likely explanation for what you're seeing is a bad ground connection at the turn signal lamp itself; that will be the black wire out of the connector for the lamp, which goes straight to a ground cluster bolted to the skin of the car. If that ground is bad, the voltage there won't be zero, it'll be some non-zero value that depends on the resistance from it to a real zero ground and the amount of current that is passing through it. Headlights off, voltage at bad ground is non-zero but low enough to allow current to flow through the turn signal lamp; headlights on and pushing more current through and the voltage at the ground drifts up high enough that it you can't get enough current through the turn signal lamp any more.

Might be something else, but that ground is where I'd start.

One other diagnostic question: Are any of the other lights acting up in any way? Headlights, parking lights? Does the four-way flasher work?
 
I'll check the voltage with my meter but I can say that "No" the hazard lights do not work but how to diagnose that issue will be my next issue....

'PeteX1/9
 
Background....

Okay so unfortunately the PO "don't ask me why he would???:confuse2:" removed the front blinkers and the side repeaters when I bought the car, he physically had all the mounting holes filled in when the car went to paint so I drilled tiny holes and installed aftermarket front blinkers.

Connected to the right blinker is only the blue wire as the other two wires coming out of the connecter I'm assuming were meant for the side repeaters. When I connected my test light to the input for the blue wire it blinked with the headlights off and blinker on and when I turned the headlights on the testlight very dim lit up but not enough to blink so your theory is correct that power is getting there but being lost somewhere when the headlights are turned on.

As for ground on my 74X the only thing connected to ground in the headlight cavity is ground from the headlight motor to the body of the car. I check the left side and same thing ground from the headlight motor to the body and all the wires coming from the blinker connector seem to go as a bunch into the loom that goes into the trunk area.

If I knew exactly which wire should be going directly to ground I would just run a new wire from it to ground. Coming from the blinker connector their are two black wires and a few of other colors. 74s dont have a ground cluster like my 84X does.

PeteX1.9
 
petex19 said:
Okay so unfortunately the :devil: :dunce:
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Sigh.... Gotta love the PO....

I've attached a snippet from the wiring diagram showing what's supposed to be in that corner. #1 is the turn signal light, #2 is the parking light, the side marker is at the bottom right, #4 is the headlight relay, and the ground point is off to the left.
Colors are Nero:Black; Grigio:Grey; Verde:Green; Giallo:Yellow; Azzuro:Blue; Rosso:Red; Bianco:White.

All the blacks are grounds.

your theory is correct that power is getting there but being lost somewhere when the headlights are turned on.
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Not my theory, Steve and Greg's. But what you've found is pretty much smoking gun for a bad ground.



 
Thank you very much for the schematic, my Haynes manual has the same diagram but I don't recall seeing the headlight relay that is off to the left in your diagram with the ground. I will definetely check the ground for the relay under the dash next as in the headlight cavities the only ground points are to the body from the headlight motors and they are good. I did also notice that even with the headlights off although the right does blink and chime inside the car it still isn't as pronounced as the left side, a little slower and a little quieter then the left so could it be my flasher relay although it may work it may be slowly dying???

'PeteX1/9
 
petex19 said:
I did also notice that even with the headlights off although the right does blink and chime inside the car it still isn't as pronounced as the left side, a little slower and a little quieter then the left so could it be my flasher relay although it may work it may be slowly dying???
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That is EXACTLY what a bad ground in the right-hand compartment will do - the bad ground behaves like a resistor in the circuit: reduces current flow so dimming the light and slowing the blink rate.

A bad flasher relay is much more likely to affect both sides equally.
 
Am I missing something, is there another ground in the headlight compartments other then the headlight motor ground? I removed that ground and sanded the body down to bare metal and re-attached the ground wire and still nothing. I could try attaching to a new spot on the body and give that a go.

'PeteX1/9
 
Most likely the ground is bad at the bulb socket. Clean the socket and replace the bulb just in case.
 
Matthew said:
Most likely the ground is bad at the bulb socket. Clean the socket and replace the bulb just in case.
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Since the turn signals work when lights are off, the socket is probably OK.

petex19 said:
Background....
...so I drilled tiny holes and installed aftermarket front blinkers.
Connected to the right blinker is only the blue wire as the other two wires coming out of the connecter I'm assuming were meant for the side repeaters.
PeteX1.9
Click to expand...

How are the new after-market blinkers grounded? How many wires come out of the new blinkers? Do the new blinkers have one or two bulbs? If only one bulb, is it a dual filament bulb?
 
ng_randolph said:
Since the turn signals work when lights are off, the socket is probably OK.
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Agree - the bad ground explanation requires that the headlights are adding current somewhere upstream of the offending ground. Y'know, it might be time to try swapping the bulbs between the two sides. Also clean every connection in the path to that light.

Of course Italian electricals routinely make fools of all logical diagnosticians, so here's another trick worth trying:

Slaughter a black rooster (a black goat is probably overkill) at midnight. Drip some of its blood on the bad signal light; wrap the body of the rooster in a piece of paper on which you've written the VIN of the car; then bury it (the rooster, not the car!) with its head facing in the direction of Turin. Next full moon the electrical system will start working again.
 
That is awesome, either you are a true Italian or have spent alot of time around them.:excited:

I'm Sicilian and my dad is always talking about moons, LMAO!!!!

I don't know what I would do without this amazing group of XWeb'ers, I'll try all the amazing tips first chance I get.

'PeteX1/9
 
The new blinkers are from "Princess Auto" and have only one wire coming out of them that I've attached to the blue wire so essentially no ground directly from the blinker itself I guess? I just assumed that the circuit was grounded somewhere along the way between the blinker light and the fuse panel and switch.

'PeteX1/9
 
There has to be a ground connection to the blinker, so it must be relying on getting ground through the mounting screws. What are the blinkers mounted to? Any reason to suspect that it would not get good ground that way?

You said the right blinkers don't work when lights are turned on, does that mean right rear blinkers also don't work when you turn on the lights?
 
Yes the aftermarket blinkers must be grounded through the mounting screws and No the rear blinkers do not work either or is there any blinking chime heard inside the car but you turn the lights off and the blinker works perfectly in the front and the rear???

The blinker is screwed directly to the body metal in the original location area in the front. I don't know how to trace the problem or fix it but obviously when the headlights are turned ON the power is dead to the right blinkers front and back so are the front and back right side on the same circuit and if so should I be looking for a bad ground in the back of the car (i.e. the rear blinkers ground???)

'PeteX1/9
 
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