Author Topic: A Few Thoughts on Turn Signal Troubleshooting  (Read 1141 times)

rich69rs

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A Few Thoughts on Turn Signal Troubleshooting
« on: July 15, 2022, 09:18:07 PM »
From time to time, questions arise on the forum regarding turn signal, brake light, etc. trouble shooting.  I recently had an issue with my left front turn signal so I thought I'd share the approach I used to identify, isolate, and resolve the issue - perhaps someone else may benefit.

My car is a 1969 Norwood built, 01C, Rally Sport.

Before beginning any electrical troubleshooting, I strongly recommend obtaining a complete package of the colored wiring diagrams for your car!!  Tracing wiring with these colored diagrams is infinitely easier than trying to use black and white diagrams.  Having these color coded wiring diagrams will save you time and headaches.

1969 Camaro - Both the left and right FRONT turn signals function as follows:

I.   Switched 12v source from the Fuse Panel supplies power via a 12 gauge pink wire to the turn signal flasher which is located under the dash on a support near the ash tray.

II.   14 gauge purple wire from the turn signal flasher supplies power to the turn signal switch in the steering column via the flat connector on the right side and toward the base of the column.

III.   When the left turn signal is switched on, power is supplied via the turn signal switch through the flat connector to two 20 gauge wires:
      a) light blue wire for the left front, and
      b) a yellow wire for the left rear. 
Both wires connect to separate terminals on the dash side of the bulkhead connector at the firewall.

IV.   An additional 20 gauge light blue wire connects to the light blue wire terminal on the dash side of the bulkhead connector and provides power to the left turn signal indicator light in the instrument panel.

V.   Focusing on the front left turn signal; the 20 gauge light blue wire continues from the engine side of the bulkhead connector to the front of the left inner fender where it connects to the left turn/park lamp assembly wiring harness via a "T-Connector". 

Richard Thomas
1969 RS

rich69rs

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Re: A Few Thoughts on Turn Signal Troubleshooting
« Reply #1 on: July 15, 2022, 09:19:21 PM »
Over the last few weeks my left turn signal had become intermittent and then finally quit working altogether. 

When it quit working, what I observed when the left turn signal was switched on was:
  a) no turn signal flashing
  b) the left front the turn signal not on
  c) the left rear turn signal is on steady, not flashing
  d) the left turn signal indicator light in the instrument panel was constantly on but dimly illuminated. 
This is what one typically would observe if a bulb has burned out and created an “open circuit”.  Since the signal indicator light is illuminated, it is also a direct indicator of power at least as far that point.

If I pull the headlight switch out to “park” position, both the front and rear, left and right parking lights come on.  Also, since both front parking lights come on with the headlight switch in the “park” position, the problem most likely is not a ground problem.  If there was a bad connection between the socket and ground, one would expect that neither the parking lights nor turn signal lights would function properly.

First thing to check was the front left turn signal/parking light bulb.  When I removed it, both filaments looked good.  I confirmed that the bulb was good by using a multimeter and checked for continuity between each two contacts on the bottom of the bulb and the metal side of the bulb.  Bulb checked good.  The problem is not a burned out light bulb. 

For the next step, both the front left and right turn signal/parking light bulbs are removed.

Next I turned on the parking lights and checked for voltage between the left socket contact and ground on the driver’s side.  I also made this measurement on the passenger side.  In both cases, it was essentially 11.5 vDC, which is what I expected since both of the front parking lights were functioning properly.  I turned the parking lights off.

I turned the ignition switch to the “ON” position and turned the left turn signal on.  I measured the voltage between the right socket contact and ground and on the driver's side got 0 vDC.  I turned the right turn signal on and made this same measurement on the passenger side and got 5.5-5.65 vDC.

(Note:  when looking at the front of the car and at the parking/turn signal light socket, the parking light is the left contact and the turn signal is the right contact.  Refer to Photo #1.)

« Last Edit: July 15, 2022, 09:41:05 PM by rich69rs »
Richard Thomas
1969 RS

rich69rs

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Re: A Few Thoughts on Turn Signal Troubleshooting
« Reply #2 on: July 15, 2022, 09:20:40 PM »
At this point, I know that I do not have voltage at the turn signal contact.  Next step is to identify and isolate where the problem is.  To accomplish I had to move up the harness to the “T-Connector” between the forward lamp harness and the parking light/turn signal harness.  It is located at the inner fender near the front left of the car.  Refer red circle in Photo #2.
Richard Thomas
1969 RS

rich69rs

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Re: A Few Thoughts on Turn Signal Troubleshooting
« Reply #3 on: July 15, 2022, 09:25:03 PM »
Since my car is a RS, there were a couple of additional steps necessary to access everything.  The vacuum tank for the hideaway headlights is mounted to the inner fender directly above this connector.  It had to be removed in order to access the “T-Connector”.  From underneath, I also removed the gravel shield which covers and protects the headlight door actuators.

With the vacuum tank removed, I was able to separate the “T- Connector”.  At the forward lamp harness side of the connector, the top or horizontal portion of the connector has the light blue turn signal wire while the vertical portion of the connector has the brown parking light wire.  A second brown wire also runs from this connector to the passenger side parking light.

I turned the ignition switch to the “ON” position and turned the left turn signal on.  I measured the voltage at the light blue wire on the forward lamp harness side of the connector and got 5.9 vDC.  This was what I was hoping to find; i.e. that I had voltage all the way to this connector and that the problem was in the parking lamp/turn signal assembly and harness.

I removed the parking lamp/turn signal assembly and harness and went over to the bench to find out exactly where the problem was.

The two wires in the parking lamp/turn signal harness are essentially enclosed in a protective sheathing and only at the “T-Connector” can one actually see the wires.  What you see are a purple wire and a black wire, not light blue and brown.  The purple wire is parking lights and the black wire is turn signal.  Refer to Photos #3 and #4.

I assume Chevrolet did this for a couple of reasons.  1)  The wire colors really didn’t matter since they are essentially hidden by the outer protective sheathing.  2)  More importantly, if Chevy manufactured this harness with the same two colors then they would have one assembly, p/n 916911, which could be used on either side as opposed to making one harness with light blue wire for the driver’s side and a second harness with dark blue wire for the passenger’s side.  Just something to note and be aware of; i.e. the wiring diagram color coding actually ends at the “T-Connector” not at the parking/turn signal assembly socket.

Richard Thomas
1969 RS

rich69rs

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Re: A Few Thoughts on Turn Signal Troubleshooting
« Reply #4 on: July 15, 2022, 09:26:15 PM »
There was no evidence of an issue with the wiring at the “T-Connector”.  I then looked to see if the wires appeared to be intact at the socket.  To do this I had to slit the outer sheathing slightly.  Everything looked fine at the connector.  I next decided to look at the wiring inside of the plug/grommet which is shown in Photo #2 below the “T-Connector”.  This took a little doing since the plug/grommet had been fused to the two wires during assembly in order to prevent the wires from sliding through the grommet which also allowed the plug to become a point of support for the harness.  After carefully slicing the plug/grommet open, the point of failure was obvious.  The black (turn signal) wire had damaged insulation and badly frayed wiring which had finally broken after 53 years.  The insulation on the purple (parking lights) wire was also slightly damaged. 

I cut out the damaged sections of both wires and soldered in new splices with shrink wrap.  I also added new external shrink wrap to cover the original outer sheathing and places where I had cut it for inspection purposes.  Refer to Photo #5.  As can be seen Photo #5, the plug/grommet was reinstalled back on the harness in its original location.  Epoxy glue was used to fill the inside of the plug/grommet and secure it to the two wires.  A tie wrap was temporarily installed, as shown in the picture, in order to keep the plug/grommet (which I had previously split open) closed until the glue had set up about an hour later.  At that point, the parking light/turn signal assembly and harness was reinstalled in the car and tested.  Everything worked fine.  The left turn signal was now functioning as it should.
« Last Edit: July 15, 2022, 09:46:17 PM by rich69rs »
Richard Thomas
1969 RS

rich69rs

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Re: A Few Thoughts on Turn Signal Troubleshooting
« Reply #5 on: July 15, 2022, 09:26:59 PM »
As a footnote, I would strongly recommend repairing your existing assembly if possible.  Reproduction pieces, including OER, do not provide the protective sheathing as originally designed.  This sheathing not only protects the wiring which would otherwise be exposed to road and weather, but also seals at the back of the socket in order to help keep the elements from intruding.

Richard Thomas
1969 RS

Chuckman4112

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Re: A Few Thoughts on Turn Signal Troubleshooting
« Reply #6 on: July 15, 2022, 11:47:16 PM »
Nice work and post.
Chuck

68 Camaro SST 350/TH400

 

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