Random speed turn signals?

[chaseincats]

Hi guys,

So got a weird one for you.  We've been doing some work on a 1974 260z and the turn signals on the car don't blink in a standard rhythm.  They randomly blink super quickly, super slowly, and everything in between when engaged with the signal stalk.

I'm guessing this is a grounding issue with the turn signal stalk itself, right?  I can't seem to find where the turn signal grounds out to , does anyone know?

 

Any ideas?

-chase

[SteveJ]

Is the car running? Does the rate of blinking correlate to engine speed? How old are the flasher relays? What modifications have been made to the car? Does it still have incandescent bulbs, or have they been swapped over to LEDs?

This has NOTHING to do with the turn signal switch. There is no ground for the circuit at the switch.

You should download the service manual from this site. The BE section has some excellent breakouts of many of the circuits, including the turn signal circuit. It helps a lot in troubleshooting.

[chaseincats]

2 hours ago, SteveJ said:

Is the car running? Does the rate of blinking correlate to engine speed? How old are the flasher relays? What modifications have been made to the car? Does it still have incandescent bulbs, or have they been swapped over to LEDs?

This has NOTHING to do with the turn signal switch. There is no ground for the circuit at the switch.

You should download the service manual from this site. The BE section has some excellent breakouts of many of the circuits, including the turn signal circuit. It helps a lot in troubleshooting.

The car does run and the rate does not correlate to engine speed.  The flasher relays are most likely original (that said so are mine and they work fine).  There are no electrical modifications to the car and the bulbs remain incandescent.  

I have the FSM but I wasn't sure if the switch had a ground itself down the loom as there are quite a few ground symbols on its wiring diagram page.

[SteveJ]

First, the FSM clearly identifies two ground points for this circuit. One is in the engine bay, and the other is by the taillights. They are identified at Earth Point.

Let's talk about theory of operation as designed. When the turn signal switch is moved up or down, it completes the circuit for the right or left side respectively. Using a positive to negative flow, we can trace voltage from the battery, to the starter, through the black fusible link, through the shunt, through the green fusible link, through the ignition switch, through the fuse box, through the hazard switch, through the flasher relay, and to the turn signal switch. After the switch, you just have the bulbs, ground, and back to the battery.

As current flows through the circuit, the bimetal strip in the flasher relay heats up (power= current x voltage). Due to the nature of the bimetal strip, the heat causes the strip to move away from the contact, and that opens the circuit. The strip quickly cools down, and it makes contact again, heating it with the current flow.

So, since you said the blinking speed did not vary with the engine speed, let's break this down into the elementary factors of resistance, current, voltage, and power. The resistance is primary from the bulbs. It can be considered constant. The current that causes the bimetal strip to heat up is voltage divided by resistance.

This gives us two things to check in this circuit:

1. The voltage in the circuit: Measure voltage to ground while the turn signals are operating and see if there are voltage fluctuations. Higher voltage would, in theory, give a faster blink rate.
2. The condition of the flasher relay: See if the hazard lights exhibit the same behavior as the turn signals. If they don't, swap the two flasher relays and see if the problem follows the flasher relay.

[chaseincats]

12 hours ago, SteveJ said:

First, the FSM clearly identifies two ground points for this circuit. One is in the engine bay, and the other is by the taillights. They are identified at Earth Point.

Let's talk about theory of operation as designed. When the turn signal switch is moved up or down, it completes the circuit for the right or left side respectively. Using a positive to negative flow, we can trace voltage from the battery, to the starter, through the black fusible link, through the shunt, through the green fusible link, through the ignition switch, through the fuse box, through the hazard switch, through the flasher relay, and to the turn signal switch. After the switch, you just have the bulbs, ground, and back to the battery.

As current flows through the circuit, the bimetal strip in the flasher relay heats up (power= current x voltage). Due to the nature of the bimetal strip, the heat causes the strip to move away from the contact, and that opens the circuit. The strip quickly cools down, and it makes contact again, heating it with the current flow.

So, since you said the blinking speed did not vary with the engine speed, let's break this down into the elementary factors of resistance, current, voltage, and power. The resistance is primary from the bulbs. It can be considered constant. The current that causes the bimetal strip to heat up is voltage divided by resistance.

This gives us two things to check in this circuit:

1. The voltage in the circuit: Measure voltage to ground while the turn signals are operating and see if there are voltage fluctuations. Higher voltage would, in theory, give a faster blink rate.
2. The condition of the flasher relay: See if the hazard lights exhibit the same behavior as the turn signals. If they don't, swap the two flasher relays and see if the problem follows the flasher relay.

Thanks for this awesome write-up - I'll pass this along to my friend.

It occurred to me today that I believe he does not have the firewall ground wire connected - could that be of consequence?  Everything seems to *work* with it having been disconnected thus far...

[SteveJ]

It is best to have all the grounds in place for testing electrical circuits.