The Stovebolt Site Forums The Shop Area The Electrical Bay Turn signal problem solving

Took a little drive in my 51 3100 yesterday. Been several weeks since I had the chance.

Truck has a very old aftermarket turn signal switch that utilizes a 3 prong flasher and has an onboard indicator light. Got it all functional 3-4 years ago. Rear signals have a separate fixture. Front signals are tied into the park lights via twin filament bulbs.

Anyway, I noticed yesterday the right signal to be done functioning as normal on the switch indicator light. The left signal would give exactly one flash, and then nothing.

I didn’t have time to investigate or troubleshoot night. Curious if this symptom points to a specific cause?

In my brain, a weak flasher would show weirdness on both left and right. Weak bulbs, in my experience, tend to do flash at a higher interval. A cut or chewed wire won’t even give a flash at the indicator…from previous experiences

Nothing like the old left arm that works perfectly every time.

99.9% of the population would just think you were waving at them.

That’s my fear. I did use the arm on this ride. But I like the turn signals.

Ya, I actually had a lady follow me into Advance Auto to ask me what my straight-up forearm meant.

Between Ol' Roy and The Phantom, I'm used to using hand signals.

Did you know that turn signals weren't required on vehicles sold in the USA until 1968? Pretty funny.

My daughter just took the CA. D.M.V. driver's permit test yesterday. That is a question on the test. All three arm signals!
Todd

It's on the Georgia test, too. Hardly anyone knows it, though.

So….

Any theories on the “one flash and done” behavior?

We did get slightly off topic, didn't we?

I think the turn signal switch you describe would have just 4 wires. It should be wired up like the drawing below.

Starting at the upper left is the supply voltage (6v or 12v, you didn't say which) that should be switched on with the ignition switch.
The supply voltage should go through a fuse and then connect to the input pin (I) of your 3 prong flasher.

The output pin (O) of the flasher should connect to the wiper connection (W) of the turn signal switch.

The pilot (P) pin of the flasher should connect to the onboard indicator light in the turn signal switch. I didn't draw it inside the turn signal switch because it has nothing to do with the operation of the system. It just shows the driver if the system is working.

The left turn wire (L) on the turn signal switch should connect to the center (only) contact of both the left front and rear turn lamps.

The right turn wire (R) on the turn signal switch should connect to the center (only) contact of both the right front and rear turn lamps.

The outer case of all 4 of the turn lamps need to be connected to ground.

The magic of the whole system is the orange colored device inside the flasher. It is a bi-metallic strip that bends when it warms up as electrical current flows through it. As drawn, the turn signals are off and there is no current flowing. Therefore pin I of the flasher is connected to pin O and none of the turn signal lamps nor the onboard indicator lamp are on.

When the driver moves the turn signal lever to the left:

1. Current starts to flow from switched battery voltage
......through the fuse
......from pin I to pin O of the flasher
......to wire W of the turn signal switch
......through the yellow wiper of the turn signal switch
......to the L contact in the turn signal switch
......out to the left side turn lamps center contacts
......through the lamp filaments (lighting up the lamps)
......out through the metal outer shell of the lamps
......and back to the ground side of the electrical system.

2. The left front and rear turn lamps illuminate and the bi-metallic strip starts to warm up. In about 1 second, the strip warms up enough to bend away from the O pin of the flasher and the strip contacts the P pin instead.
The left turn lamps go out because they are no longer supplied with electricity.
The onboard indicator turns on, telling the driver that the system is working.

3. I a second or so, the bimetallic strip cools down, bending away from the P pin (turning off the onboard indicator light) and making contact with the O pin, starting the whole process over again at step 1 above. This continues until the driver turns off the turn signal switch.

The bi-metallic strip depends on a certain amount of current flow to operate correctly.

A higher than normal electrical resistance anywhere in the system will cause the bi-metallic strip to take longer to switch from O to P (although the P to O switch should remain the same). An example of this being a good thing is when one of the turn signal bulbs burns out. The lower current flow will cause the flasher to take longer to warmup, signaling the driver that a lamp is burned out.

In worse cases there will not be enough heat generated it the bi-metallic switch to bend it away from the O pin at all. The turn signal lamps may show very dim or not at all.

Now back to your problem. I'd start by making sure all connections shown in the drawing are clean and tight.

Assuming you have a voltmeter to test with:

A. Turn on the key
B. put the turn signal lever in the left position
C. measure voltage from fuse I to ground. It should be real close to battery voltage. If not, stop and find out why.
D. using the lowest voltage scale on you meter measure voltage across each device in the left turn system. Any reading over a 10th of a volt or so is suspect
.. a. Fuse I to O
.. b. Fuse O to flasher I
.. c. flasher I to O (this will change as the flasher operates - we are looking for the low measurement while the lamps are on. If you can't get a good measurement take on of the left side turn signal lamps out which will slow or stop the action of the flasher)
.. d. flasher O to turn signal switch W
.. e. turn signal switch W to turn signal switch L
.. f. turn signal switch L to left front turn signal lamp center contact
.. g. left front turn signal case to a good ground
.. h. fuse I to left front turn signal lamp center contact
.. i. turn signal switch L to left rear turn signal lamp center contact
.. j. left rear turn signal case to a good ground

Now repeat A through D. j. using the right turn system.