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Grey's truck's turn signals work fine when the engine is not running. . The battery reads 12.4 volts When it is running and the voltage reads 14.5 volts, they do not work. I have replaced most bulbs with LED's and replaced the flasher with a compatable one. Is it time to start easter egg hunting for a more robust flasher? Or am I missing another issue? Tks
Grey's truck's turn signals work fine when the engine is not running. . The battery reads 12.4 volts When it is running and the voltage reads 14.5 volts, they do not work. I have replaced most bulbs with LED's and replaced the flasher with a compatable one. Is it time to start easter egg hunting for a more robust flasher? Or am I missing another issue? Tks
Can you add more information on the flashing unit you are currently using.
Does it have a separate ground wire, or just your basic 2 prong design.
Here's what I mean, with the extra ground wire.
Might be worth a try.
I personally just use regular bulbs, so maybe someone else has a better idea.
Jim
Edit: do your 4 way flashers work?
Last edited by JimsRebel; Oct 4, 2025 at 09:45 PM.
Yea, I only use regular bulbs too. Why take the chance using LED's.
Same here and I pull a trailer on weekends and it flashes the same with trailer plugged in or not.
I am guessing it is a HD flasher it was one that came with either my truck or the parts truck and looked like it was good is what I went with.
Dave ----
I’m no fan of retrofit LED bulbs. The QC and reliability of them is pretty dismal.
To work on vehicles that have bulb failure warning, most LEDs have extra circuitry built in to mimic regular incandescent bulbs. Just a hunch, but I think it’s this extra wizardry that causes trouble with simple flasher circuits. It’s supposed to work in theory, but not always in practice.
Where does this leave you? If you’ve absolutely positively gotta have them spiffy LEDs, try a different brand of flasher. Make sure it’s rated for LEDs. If still no help, try another brand of LEDs. Maybe the problem is the bulbs, not the flasher. Unfortunately for your wallet, it’s all guesswork.
An issue I discovered recently when rewiring my boat trailer with LED tail lights was LEDs can't be tested for continuity. They are open circuit until voltage is applied and the diode closes making the circuit. They are good for trailer lights and your flasher won't even know there's extra load back there and will flash at the same rate as the truck signals. Good for trailers but could cause issues for circuits designed for incandescent.
An issue I discovered recently when rewiring my boat trailer with LED tail lights was LEDs can't be tested for continuity. They are open circuit until voltage is applied and the diode closes making the circuit. They are good for trailer lights and your flasher won't even know there's extra load back there and will flash at the same rate as the truck signals. Good for trailers but could cause issues for circuits designed for incandescent.
You can test for continuity if you have a diode checker on your meter. And a regular ohmmeter will check them also. BUT, polarity must be observed with the meter, you will only get a reading in one direction.
You can test for continuity if you have a diode checker on your meter. And a regular ohmmeter will check them also. BUT, polarity must be observed with the meter, you will only get a reading in one direction.
Thanks Dave, I do have a diode setting. But I was using the continuity setting and that doesn't show a circuit at all. I'll fool around with the diode setting and see how that works.
Just had a thought possibly explaining why the lights misbehave only when the engine is running. A bad diode in the alternator can cause voltage spikes (and other problems not so readily obvious).
I used to suggest a method to test with a multimeter, but have come to realize not all meters can capture these spikes. This would give a false indication that all is good. Instead, I now recommend taking the truck to any place that sells batteries and ask for an AC ripple test. With the proper test equipment, which any parts store should have, AC ripple is easy to measure. If the kid looks at you funny and doesn't know what AC ripple is, thank him for his time and try another store.
If afraid you'll have to surrender your man card by asking for help (a valid concern...), you can get an inexpensive meter that will work. I've owned an ANCEL BA101 for several years and it works well. I think it set me back a whopping $40 at the time:
There are plenty of similar battery testers out there that should work. This is just one example.
Whether you do it yourself or have it done, definitely get the charging system tested. If the charging system is putting out big voltage spikes, this can cause all sorts of havoc.
One last thought: try turning the heater fan to hi speed and turn on the headlights. The extra load may help dampen the spikes, and give you an idea if AC ripple is causing trouble.
Grey's truck's turn signals work fine when the engine is not running. . The battery reads 12.4 volts When it is running and the voltage reads 14.5 volts, they do not work. I have replaced most bulbs with LED's and replaced the flasher with a compatable one. Is it time to start easter egg hunting for a more robust flasher? Or am I missing another issue? Tks
sounds like you bought a bad flasher to me. Not every flasher will work with leds.
Just had a thought possibly explaining why the lights misbehave only when the engine is running. A bad diode in the alternator can cause voltage spikes (and other problems not so readily obvious).
I used to suggest a method to test with a multimeter, but have come to realize not all meters can capture these spikes. This would give a false indication that all is good. Instead, I now recommend taking the truck to any place that sells batteries and ask for an AC ripple test. With the proper test equipment, which any parts store should have, AC ripple is easy to measure. If the kid looks at you funny and doesn't know what AC ripple is, thank him for his time and try another store.
If afraid you'll have to surrender your man card by asking for help (a valid concern...), you can get an inexpensive meter that will work. I've owned an ANCEL BA101 for several years and it works well. I think it set me back a whopping $40 at the time:
There are plenty of similar battery testers out there that should work. This is just one example.
Whether you do it yourself or have it done, definitely get the charging system tested. If the charging system is putting out big voltage spikes, this can cause all sorts of havoc.
One last thought: try turning the heater fan to hi speed and turn on the headlights. The extra load may help dampen the spikes, and give you an idea if AC ripple is causing trouble.
I gotta say ive been working on stuff for 50 years, and even some schooling back in the day. I had to look up what a AC ripple test is. Turns out ive tested for it, but never knew the name. Learn something new every day.
As for the problem. I know in the past dealing with LED's, that sometimes tossing at least one incandescent bulb in the system sometimes help issues. Kinda becomes a buffer to help the system work together.
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