Another Hazard Light Head Scratcher (1 Viewer)

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Oct 29, 2019
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Dallas, TX
Don't usually have to post anything new here as this forum is pretty darn comprehensive, but have an issue with my hazards that I can't find duplicated in any of the threads.

Basically turn signals work fine. Only front hazards working. Have looked and wiring diagram and can't for the life of me figure out how that can be. The rear lights are after market but I pulled them and checked for voltage at the connector - have it for the turn signal but not the hazards so don't think it's the light units. I did only pull one light however; maybe I need to pull them both and check for voltage.

Basically acting like a bulb is burnt in that the fronts flash at double speed but backs don't flash.

It looks like they run on all the same wiring as the turn signals and it looks like the hazard switch can only fail left vs right not front vs back so don't think the switch is the problem. So if the turns work can't for the life of me figure out why the hazards don't. Maybe something wonky with the aftermarket rear lights? But again not even getting voltage back there.

I think next step is to pull both rear lights and check voltage. If that doesn't do it then I'm at a loss.

Any insight would be greatly appreciated.
 

Shark56

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Year of 40?
99 percent of light problems are grounds if the bulbs are good. Check the other bulb also.
 

Cromagnon

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Year and model would help us help you. If the rear turn signals work then it isn't the rear fixtures. You have a wiring or hazard switch problem. What changed to cause this i.e. what did you or someone else do? Go to the last known good configuration, restore that, and see if the problem goes away.
 
Joined
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Messages
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Dallas, TX
Sorry about that, 78 FJ40.

Just bought it little less than a year ago. Honestly never checked the hazards but coming up on inspection so flipped them on noticed the problem. So not sure when it started.

It looks like the right and left circuits are independent however, and fronts are linked to backs on each side so can't think of a reason, if I had a short somewhere, that it wouldn't also show up in the turn signals.

I was reading somewhere that the bulb requirement for the hazard is different than the turns so that's only thing I can think of given after market fixtures (which are self contained looks like LED type). But the turns and the hazards energize the same wire and with the fixture out it's getting nothing with hazards on.

I did notice the hazards are connected to the parking brake light circuitry, which acts a little wonky on mine. But don't think that's affecting it.

The replacement tail lights look like these. These are marketed as FJ40 replacements from Metal Tech. Connectors look pretty much identical to these.

1600101194172.png
 

Cromagnon

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I did notice the hazards are connected to the parking brake light circuitry, which acts a little wonky on mine. But don't think that's affecting it.
The load resistor will not fix this problem.

The parking brake warning light should not be connected to the hazard switch. Do you have a wiring diagram?
 
Joined
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Messages
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Location
Dallas, TX
I have a wiring diagram. I don't see it actually being connected, it just looked like it ran off the same power source in the wiring diagram. So I thought maybe they connect somewhere.

How do I get the hazard switch out?
 

Cromagnon

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Remove the knob and then the "nut" with two holes in it. It probably is technically a bolt but you will understand once you have it off. The two wholes are for a spanner.
 

Cromagnon

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The power for the hazard side of the switch is powered from the stop light circuit. The turn signal side of the switch is powered from the turn/heater circuit.
 
Joined
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The power for the hazard side of the switch is powered from the stop light circuit. The turn signal side of the switch is powered from the turn/heater circuit.
Yep see that in the diagram. I'm getting voltage in and out of the flasher unit for both hazards and turns, just cycles faster for the hazards. But again if I have a short somewhere be it in the switch or the wiring it looks per the diagram that it would knock out one side vs the other not backs vs fronts.
 

Cromagnon

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Colorado Springs, CO
 
CORRECT!!!! You definately have a wiring problem as the hazard side of the switch feeds the left ( GB wire that goes to both the front and rear ) and the right (GY wire that goes to the front and rear,) Some PO Wizardry happening in the wiring somewhere.
 
Joined
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Messages
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So bit of an update here. I think it is in fact tied in to my parking brake light gremlin. When I step on the brakes the rear hazards work. More detail on the parking brake light gremlin. Parking brake on, light is on. Parking brake off, light is on but if you step on brakes it turns off - also if you turn or pull out the brake handle ever so slightly it also turns off. Definitely looks like the PO rewired at the very least the parking brake light switch. Understand that light also is a brake fault light too, at least it looks that way, meaning if there is a pressure fault on the master etc it's supposed to light up but my guess is if that were case moving the brake handle wouldn't extinguish it. At least making progress.
 

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