Buzz buzz blinker- electrical gremlin (1 Viewer)

[diesellibrarian]

I went through a similar issue with my house wiring. I replaced a fluorescent light fixture in my shop with an LED fixture, and suddenly my motion sensor switch no longer worked properly. I did some reading and learned that some types of relays/thermal switches rely on a certain minimum electrical load to work as designed. The LED I installed did not draw enough current to allow the switch to work properly.

I wonder if the same issue would occur in a 12v DC system? Thermal switches such as those used in the flasher circuit must be calibrated for a certain draw/resistance, no? Wondering if replacing the incandescent bulbs with LEDs reduces the draw to the point where the thermal switch can no longer develop enough heat to open the circuit, meaning that the lights stay on, or at least oscillate on/off so rapidly (hence the buzz) that it looks like they're fully on. With reduced resistance in the overall circuit (caused by the removal of the incandescent bulb), perhaps the resistor in the flasher switch can no longer build enough heat to open the switch?

 

[CruiserTrash]

I went through a similar issue with my house wiring. I replaced a fluorescent light fixture in my shop with an LED fixture, and suddenly my motion sensor switch no longer worked properly. I did some reading and learned that some types of relays/thermal switches rely on a certain minimum electrical load to work as designed. The LED I installed did not draw enough current to allow the switch to work properly.

I wonder if the same issue would occur in a 12v DC system? Thermal switches such as those used in the flasher circuit must be calibrated for a certain draw/resistance, no? Wondering if replacing the incandescent bulbs with LEDs reduces the draw to the point where the thermal switch can no longer develop enough heat to open the circuit, meaning that the lights stay on, or at least oscillate on/off so rapidly (hence the buzz) that it looks like they're fully on. With reduced resistance in the overall circuit (caused by the removal of the incandescent bulb), perhaps the resistor in the flasher switch can no longer build enough heat to open the switch?

The relay in the flasher is dependent upon current to open and close, but it’s primarily it’s own internal resistance that determines the current. A relay will have a coil and a switch contact that’s magnetic. When The coil is put into a circuit - with system voltage on one side of the coil and ground on the other - the current is determined by the coil resistance. Typically that is 50-300 ohms. The current in the coil induces a magnetic field that attracts the magnetic switch towards a contact and voila, you’ve made a connection. A bulb in series will affect the current draw, but typically the system is designed for the coil to be doing the “heavy lifting” so to speak. I do not think the bulbs are in series with the coil itself in this application. Additionally there are very few thermal switches (thermistors) in a 60 Series, and the flasher isn’t one of them. The carb cooling fan, and the two BVSVs in the thermostat housing come to mind.

All that to say I test a fair number of flasher modules/relays in my personal 60, which is fitted with LED blinker bulbs all the way around. I’m modifying the flasher modules for use with LED bulbs and I test every one after the mods. And no it’s not the “cut out the resistor mod” - folks are free to do that on their own but when the unobtainable transistors in the module get fried from too much current, I guess you have to find another module. I never have any trouble with blinker operation unless I have a cold solder joint or the contact is dirty. A quick easy touch up and then they work. That situation is very very rare.

I agree that the buzzing is likely a relay that’s trying to switch but the coil field isn’t strong enough to latch the connection. The switch itself is bouncing off the contact. That’s my theory anyway, because the noise is mechanical and the relay is an electromechanical device.

My best guess? The coil isn’t developing a strong enough field to latch the switch contact, which indicates that it isn’t experiencing the full current it was designed for. Why? Lack of voltage, likely from a faulty positive wire or a dirty ground.

V=I*R —> I=V/R
V=voltage
I=current
R=resistance

I is too low. We know resistance of the coil is fixed (and Chase has tried multiple modules to confirm that his wasn’t busted). As you can see in the equation, the higher the voltage, the higher the current. So V must be too low. What makes V too low? The wiring.

 

[CruiserTrash]

@red66toy do you have access to a DC power supply? You could put 12-14VDC on the flasher module relay and see if it replicates the buzzing. That would for sure let you know if the module is bad. Yes, there are some other things in the circuit that can make things more complicated than 12VDC, a coil, and a ground - I'll check it out when I'm able. You could also check the VDC and ground at the pins of the flashed module receptacle.

 

[red66toy]

@red66toy do you have access to a DC power supply? You could put 12-14VDC on the flasher module relay and see if it replicates the buzzing. That would for sure let you know if the module is bad. Yes, there are some other things in the circuit that can make things more complicated than 12VDC, a coil, and a ground - I'll check it out when I'm able. You could also check the VDC and ground at the pins of the flashed module receptacle.

I do, I can run that test this weekend.

 

[CruiserTrash]

I do, I can run that test this weekend.

As I recall you tested resistance between the bulb sockets and the contacts where the module plugs in right? If a wire is corroded and providing a ton of resistance, it will also “steal” the lions share of the current versus the coil. Do you have a voltage meter in the truck - like one that gives you at least one decimal place of accuracy? It would be interesting to see what the Vdrop is with the blinker on. The incandescent bulbs gave me 0.5-0.7 Vdrop. LEDs give about 0.1Vdrop. That’s system voltage and not measured directly at any of the points in the flasher circuit, so it’s more of a general system health test rather than a surgical measurement. But it could give you a rough idea of corrosion in the wiring - if you have all four LEDs in place and hit the blinker maybe you get 0.1Vdrop on one side and 0.4Vdrop on the other. That would indicate one side has more resistance from corrosion, which is going to use more current, which in turn will cause a bigger voltage drop.

(disorganized morning coffee thoughts)

 

[CenTXFJ60]

Chase, curious if you ever changed the blinker bulbs in the gauge cluster back to incandescent? I'm having the same issue on a 62 I'm working on. The owner stopped by my place the other week and swapped out all the interior bulbs with LED. Went to use the blinker for the first time yesterday and both L&R sides buzz and do not blink.

We fixed this on our end. Way too easy…swapped the LED’s out for the stock bulbs and she works again. When I figured out the blinkers with LED’s worked with the key in the ACC position but not when the truck is running I was pretty confident the additional juice was botching the system. This works out well for the owner as those LED blinkers are way too bright.