Headlight short circuit??? Help??? (1 Viewer)

Joined
Oct 31, 2020
Messages
2
Location
mid coast NSW
Hey guys,

so I’ve got a bit of a doozy I’d say.... I was installing a new set of ultra flex LED’s only to find that I’ve got a constant 12v at the headlights once I flick them on. I disconnected The main headlight relay in the engine bay and am still getting power to them and also the L/H fog light park light whatever you wanna call it... in the terminals of the relay the 2 left slots have constant power: one with +12v and the other reads -12v?

so from here I have disconnected ALL external light relays (light bar etc) disconnected the trailer harness at the rear, checked all fuses and replaced both headlight main relay and also the tail relay in the kick panel....

Still there’s a constant +/-12v at the lights when on low beam. With the new lights installed nothing comes one at low beam but when you flick to high beam they get stuck on, even if it’s just flash. I have to turn the lights off to get them to go off....

please help I’m about to cry... 🙄
 

Comet

Knower of little, master of less.
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Joined
Nov 22, 2009
Messages
2,189
Location
Southwest Virginia
Jayce, I have no idea on your set up. I do know that LED lights are polarity sensitive and some of the chinesium ones have the traditional red wire as ground. Look at the schematic again from the led manufacturer. Three wires, one common (ground) one low beam and one high beam at the termination.

BTW crying is good for the soul. Get that bad juju out and let your brain work through this.
 

ProjectsNMotion

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Sep 19, 2018
Messages
260
Location
New York
Are you sure it's the headlight relay that you're removing? Where are you measuring voltage for the headlights? Are you looking at the correct range when you measure voltage (volts vs millivolts)?

The fact that you're mentioning some negative voltages implies that you're not very familiar with a multimeter. That's okay, everybody starts somewhere. If you're measuring voltage for the headlights, you may as well attach the ground of the multimeter to the "negative" terminal on the battery. That way, all of your measurements will have a known good ground reference. Is your multimeter auto-ranging or do you have to manually set the range?

Cheers
 

ppc

M Go Blue
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Aug 18, 2003
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Nashville, TN
Keep in mind that Toyota uses ground switching not positive switching. That means 12V will always be present at the bulb. The switches control the ground side of the circuit. If there is a problem with the lights turning on with incandescent bulbs where 12V is measured at the bulb then test the ground side that has continuity when the switch is turned on and no connection when turned off. With LED bulbs the polarity makes a difference. It might be easier to only have one of the four bulbs inserted at a time.
 
Joined
Oct 31, 2020
Messages
2
Location
mid coast NSW
Thanks everyone for the replies!!



@ProjectsNMotion yeah it’s the main headlight relay in the box on the P side, I’m measuring 12v at the L/H outer light plug to both beams. Yeah it’s set to dc an it’s definitely reading 12v an I was earthing to the -ve terminal...

I’m an electrician so a got history with the multi aha it was just confusing me with the -ve symbol is all, I’m not familiar with auto electrics...



The new led’s change it from -ve switching to +ve so I’m lost with that side of it? But somethings changed because now the low beams work as do the high beams but it doesn’t switch back to low still, I gotta turn them off to reset them...?



Thanks again everyone!
 

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