Turn indicator turns on with dash lights

[Cantedvalve 128]

I am still chasing this little gremlin. Long story short (hehe, pun), my left turn indicator light in the dash comes on when I turn on the dash lights (pull the headlight switch knob).  Here’s what I have done:

• Pulled the dash harness and checked for shorts and broken wires, no issues, reinstalled
• Unplugged rear lights harness. Turn indicator went out, but so did the front marker light and parking light, which I don’t think should happen
• Pulled rear light harness. Checked for shorts or broken wires, no issues, not yet reinstalled
• Pulled front harness. So far no signs of shorts or damaged wires

And that’s where I’m at.  As I look at wiring diagrams, I am confused why the turn indicator isn’t on all the time. According to what I can tell, it’s on when the side markers are on. If I turn on the lights, and the side markers come on, I’d expect the turn indicator to turn on as well, given it’s tied together.  So in that sense, I have no idea why it worked before. But it did. 

Help?

[bigmal 225]

I have had a similar problem. For me it was a bad earth at the indicator light. Try a wire with two alligator clips and give your light a direct earth. Go from light to light and see if it cures the problem. Worked for me.

[Midlife 814]

5 hours ago, bigmal said:

I have had a similar problem. For me it was a bad earth at the indicator light. Try a wire with two alligator clips and give your light a direct earth. Go from light to light and see if it cures the problem. Worked for me.

That doesn't work for side marker lights for 70's, as there is no ground for them: they use running lights/turn signals as the two leads.

CV: plug back everything in and start removing bulbs one at a time: somewhere there's a bulb causing lines to cross.  Once the bulb is out that fixes the problem, then that socket is where the problem is.

[Cantedvalve 128]

@Midlife   You keep telling me that... I keep forgetting to listen.  I’m off to do that.  Assume we are talking about the dash cluster bulbs? Oh hell I’ll check them all

So next question before I head over.  Why would the parking lamp stop working when I disconnected the rear lights harness?

@bigmal   As the vaunted shorts checker said, 1970s have really funked up turn circuits.  Yes, I did misspell that on purpose.

[Cantedvalve 128]

I ran out of wire wrap...

[gordonr 4]

On a normal unmodified (incandesant) car that would normally mean the left front park/turn socket has a bad ground.  Because of loss of ground the park light power passes thru to the turn signal element in the bulb  instead of the socket base ground then back up the wiring to the dash and it illuminates the indicator.

[Midlife 814]

3 hours ago, gordonr said:

On a normal unmodified (incandesant) car that would normally mean the left front park/turn socket has a bad ground.  Because of loss of ground the park light power passes thru to the turn signal element in the bulb  instead of the socket base ground then back up the wiring to the dash and it illuminates the indicator.

And that's why I recommend removing bulbs one at a time on each side to see where the problem socket lies/lays/laid/awww...scheiss!  However you spell that damn word.

[Cantedvalve 128]

8 hours ago, gordonr said:

On a normal unmodified (incandesant) car that would normally mean the left front park/turn socket has a bad ground.  Because of loss of ground the park light power passes thru to the turn signal element in the bulb  instead of the socket base ground then back up the wiring to the dash and it illuminates the indicator.

I did have a filthy disgusting side marker socket. Replaced that.  The lamp assembly is newer... but that doesn’t really mean anything.  It could still be bad.  Once I get the wiring back in, I’ll check out the bulbs.

[gordonr 4]

Try unscrewing the left front lens coverto expose the 1157 bulb. Using a test light and park lights turned on touch your test light probe to light bulb base if it lights the ground is bad. As a tip always verify  that your test light operates from the ground point you attached the alligator clip to before testing. 

[Rich Ackermann 174]

The 70 side marker wiring is a rube golderberg. Ford engineers were trying to be clevor by making the side markers blink alternately with the front and rear markers. I don't care if the side markers flash alternately with the front and rear markers. So, I just converted my 70 parking light wiring over to work as it does in a 69 and 71-73 years. I used 69 front markers with three wire plugs (the plug includes the ground wire whereas the 70 marker does not). I changed the 70 front marker harness from a two plug connector to a three plug and wired the third plug wire (ground) from the 69 front marker to chassis ground by way of the new three plug connector on the 70 harness . I then rewired the LH green/white and RH blue/white front and rear side marker wires to go to chassis ground. I left the brown (parking light) wire alone as it is. That's all. Now the side markers work only as parking lights and no longer flash alternately with the front and rear markers (same as it does on the 69, 71-73 cars), and chasing down ground and bulb issues is much more straight forward and easier. 

[Cantedvalve 128]

Amen brother. Ford was too cute with it by half.

[Cantedvalve 128]

I’m renaming the post to remove left, because now the RIGHT side is doing it. 

So the left side stopped once I put the harnesses back in and replaced all 8 bulbs. Now, the side markers are all bright (except the passenger rear, more on that in a second). The left indicator light is off, but now the right is lit!

Rear marker light on passenger side isn’t working. I switched out a known good bulb and it is still not working.  Front marker is working. Parking lamp is working. No idea what the problem is. I played musical bulbs, but nothing changed. 

Help

[Cantedvalve 128]

Okay... so it seemed as if the disconnect was between the front harness and the dash harness - the white/blue wire provides ground for the marker lamps, but power for the turn indicator (blinks with the parking lamp). This doesn’t explain how I have power to it when the lights are on, but I’m gonna ignore that for now hoping that fixing the rear marker fixes that too.

So I checked the brown wire at the passenger rear marker socket. 12V... good.  Then I checked the white/blue wire for ground (which it should be when just the lights are on, no turn signal).  Nothing. Okay... so back tracing that, the next place to check is the red plug under the dash where the rear harness plugs into the dash harness. No ground there either... huh. So I checked for continuity between the red plug on the dash harness and the turn signal indicator wire. Good there. So it appears that the dash harness is indeed okay, but the ground connection isn’t being made. Maybe I put the pin in the wrong hole (hehe... ) when I reassembled the front light harness. That is my next check... after I change the spark plugs in my sister’s Jeep.

[Midlife 814]

How many times do I have to tell you?  There is no ground on the 70 side marker lamps, only a difference in voltage between the brown (running lights) and the turn signals. 

[Cantedvalve 128]

Yes I understand that... but it is effectively a ground for my trouble shooting purposes.

[Midlife 814]

Yes, but you should not measure continuity between that socket pin and chassis ground.  You can only measure voltage on each pin to verify proper operation. 

[Rich Ackermann 174]

1 hour ago, Cantedvalve said:

Yes I understand that... but it is effectively a ground for my trouble shooting purposes.

As Midlife states, when you ground  either socket pins you are essentially completing the circut directly at that bulb which circumvents the way the system would seek ground normally. It will always test good that way. Remember the brown parking wire is positive and seeks ground thru the white/blue and white/green passing thru other bulbs to get there. That ground connection can come from the ground wire for the hood signal lights if you have them or the dash ground, etc.

The directional switch in the column plays games with the + and - when LH or RH the blinker is on. It's a mess, if you ask me.

[Cantedvalve 128]

Found it... white/blue wire broken at the parking lamp connector.  There are two that come out of that connector together... the one that goes under the dash is broken out.

[Cantedvalve 128]

44 minutes ago, Rich Ackermann said:

As Midlife states, when you ground  either socket pins you are essentially completing the circut directly at that bulb which circumvents the way the system would seek ground normally. It will always test good that way. Remember the brown parking wire is positive and seeks ground thru the white/blue and white/green passing thru other bulbs to get there. That ground connection can come from the ground wire for the hood signal lights if you have them or the dash ground, etc.

The directional switch in the column plays games with the + and - when LH or RH the blinker is on. It's a mess, if you ask me.

Yeah I’ve got a working knowledge of the circuit now.  I did find the problem... broken wire at the parking lamp, which was preventing the rear marker lamp from getting ground.  Now to fix it.

I understand what both of you are saying.  I did check voltage across the light first, got nothing. I then checked the brown wire, got 12V. After that I checked the continuity of the white/blue wire to chassis ground and got no continuity.  Right or wrong, that test put me on track to finding the issue, be it dumb luck or what have you.

Thanks for the help!

[Rich Ackermann 174]

On 4/7/2019 at 9:07 PM, Cantedvalve said:

Yeah I’ve got a working knowledge of the circuit now.  I did find the problem... broken wire at the parking lamp, which was preventing the rear marker lamp from getting ground.  Now to fix it.

I understand what both of you are saying.  I did check voltage across the light first, got nothing. I then checked the brown wire, got 12V. After that I checked the continuity of the white/blue wire to chassis ground and got no continuity.  Right or wrong, that test put me on track to finding the issue, be it dumb luck or what have you.

Thanks for the help!

Glad you found it. Sometimes it's hard to chase down those electrical gremlins.

[Cantedvalve 128]

I was working on the harness yesterday. The break was at/in the connector on one of the white/blue wire. I started looking... the other one was crunchy as well when I handled it, and it pulled right out too. So seeing as this happened on the right side, I replaced both sides with weatherpack connectors, and removed the same molded style connectors from the headlight circuit as well. Those I just spliced together. Not sure why the connector on the headlight harness was necessary to begin with. Seems like just another thing to chase.

[Cantedvalve 128]

Reinstalled the front lighting harness and parking lamps.  Everything works perfectly now.  So to recap, the things I found were:

• a broken wire on the passenger side parking lamp plug.  This caused the rear marker light to not work, and also caused the right turn indicator to turn on with the parking lamps.
• a badly corroded bulb in the driver parking lamp.  This caused dim lights on the driver side, and the left turn indicator to turn on with the parking lamp

With those items fixed, I have been able to reassemble the dash.  I also eliminated the unnecessary molded connectors in the headlight wiring to avoid this kind of issue in the future.