Turn signals don't work when headlights are on

[aolitesnsirens]

He fellas, so I've got a 77 Chevy K10 short bed stepside project that's almost done. I've converted all the incandescent bulbs to LED's and also changed out the turn signal and hazard relays to accept the new LED voltage. Everything is working great during the daytime. When I turn on my headlights, the dash lights come on as they should and also the turn signal lights on the dash light up, but my turn signals or hazards don't work. I can't seem to figure out why?? Everything works fine other than that. Could something be cross wired somewhere and sending power to the turn signals only when the headlights come on?? I'm stumped on this one. Any help would be greatly appreciated.

 

[Rickf]

Try replacing the side marker LED's with incandescent bulbs and see if the issue goes away. You may have the wrong type of LED's.

 

[aolitesnsirens]

Try replacing the side marker LED's with incandescent bulbs and see if the issue goes away. You may have the wrong type of LED's.

So it was the side markers. I’ve since ordered new LED side markers and I hope that fixes the problem. Thanks for the help.

 

[Ricko1966]

So it was the side markers. I’ve since ordered new LED side markers and I hope that fixes the problem. Thanks for the help.

The way the side markers are wired on these trucks is very unusual they pull ground in different polarity depending on if the turn signal is on.Most cars don't change bulb polarity,and most LEDs are polarity sensitive. You'll need polarity neutral bulbs.

 

[goldpack]

others here have typed of this, its a HD wire harness for the headlights, so it replaces the old wires and re-routes power, not sure if that would be a fix for you, ...or if there are similar harnesses

but maybe someone smarter than me will type.

https://www.lmctruck.com/electrical/wiring-components/vn-1971-12-heavy-duty-headlight-harness

 

[Ricko1966]

others here have typed of this, its a HD wire harness for the headlights, so it replaces the old wires and re-routes power, not sure if that would be a fix for you, ...or if there are similar harnesses

but maybe someone smarter than me will type.

https://www.lmctruck.com/electrical/wiring-components/vn-1971-12-heavy-duty-headlight-harness

That's not going to help him. His problem is with the side marker bulbs,he used leds and leds are polarity dependant. The problem is the side markers need bulbs that aren't polarity sensitive.

 

[shovelbill80]

others here have typed of this, its a HD wire harness for the headlights, so it replaces the old wires and re-routes power, not sure if that would be a fix for you, ...or if there are similar harnesses

but maybe someone smarter than me will type.

https://www.lmctruck.com/electrical/wiring-components/vn-1971-12-heavy-duty-headlight-harness

A relay harness will absolutely upgrade the headlight circuit, giving you more voltage to the bulbs and saving your switches.

A well-built harness using 12 and 14-gauge quality wires, or even 10/12, 'made in Germany/EU', Tyco-Bosch relays(ie, https://terminalsupplyco.com/Store/Default.aspx?CAT=EC070010), ceramic connectors...all soldered and shrink-wrapped is the way to go. Yes, the LMC harness is 'cost-effective,' and it works, but it's really junk, all things considered. You could build your own, but buying a pre-made, proper harness is a lot easier than sourcing all the parts....expect to pay +/- $175 for one.

Here's an example of a higher-end harness, and they sell lots of 'wiring' stuff: https://ceautoelectricsupply.com/headlight-relay-kits/h4-sealed-beam-headlight-relay-kits/

A fantastic harness, built for the Toyota community, can be adapted to our trucks: https://www.headlightservices.com/index.html

Unless something has changed, as far as I know, Hella relays are all made in China...caveat emptor. Keep spare Bosch units in the glove box, lol...

 

[shovelbill80]

That's not going to help him. His problem is with the side marker bulbs,he used leds and leds are polarity dependant. The problem is the side markers need bulbs that aren't polarity sensitive.

In all the decades in these trucks, I never knew that...I also never tried to use LED 'bulbs,' either. Thanks...

 

[gofone]

I had that exact problem with my 87 last month. I had to go back to regular bulbs in the front turn signals

 

[NLD79K10]

You could try and put a bridge rectifier in the feed of the LEDs, this way polarity should stay the same for the LEDs irrespective of whether the headlights are on or not.