Turn signal INOP with Headlights on? (2 Viewers)

[atoyot]

When I power my left front turn signal on my '73 FJ40 with the headlights or parking lights on it will not flash. With the headlight switch fully off it works fine. All other signals work as they should. I checked the wiring, fuses, bulbs.

What am I missing? I'm thinking either the headlight switch or a bad ground. What do you think?

 

[Aalien]

My first guess would be that the signal itself has a poor ground. With a basic probe tester see if the signal wire is actually loosing power when the park lights are on. A poor ground could cause the signal to backfeed through the park curcuit to find its ground, if this happens when you turn on the park lights you are effectively disconnecting its ground. I have repair trailer wiring that has acted just like this, the park light even still worked, but when tested the wrong filement was on. Jump a new ground wire (directly to the bulb) as a test. A bad bulb (broken filament contacting the other filament) can also act the same.

 

[Trollhole]

My first guess would be that the signal itself has a poor ground. With a basic probe tester see if the signal wire is actually loosing power when the park lights are on. A poor ground could cause the signal to backfeed through the park curcuit to find its ground, if this happens when you turn on the park lights you are effectively disconnecting its ground. I have repair trailer wiring that has acted just like this, the park light even still worked, but when tested the wrong filement was on. Jump a new ground wire (directly to the bulb) as a test. A bad bulb (broken filament contacting the other filament) can also act the same.

Gremlins!

On mine if the temp guage is working the left blinker light will work. When it stops working then the blinker on the left turn signal will not blink though the markers blink.

 

[Pin_Head]

The turn signals have to draw a certain minimum amount of current to trip the OEM flasher. When you turn the lights on the voltage drop is just enough so that not enough current flows.

You shouldn't have that much of a voltage drop if the alternator is working. Does it only do it at idle? If so, I would suspect that there is a bad/corroded/high resistance somewhere in the turn signal circuit. If it also does it at RPM > 1,000, I would suspect the battery ground or the ground strap between the engine and the frame. A bad/weak battery is also a possibility.

 

[Aalien]

If the left rear flashes with the park/headlighs on then it is not a voltage issue.

 

[Lashcat]

I am looking for that same gremlin. I know it is a bad ground to the left front blinker. Flashers work fine. I just have not dug into the wiring to find the loose ground. Sometimes if I hit a bump it will start to work. I am going to pull the blinker relay and clean it up. Heck it may be the relay. If I tap on it it will blink. Also the the blinker light in the cab will come on and stay on like I have a bad bulb , bit I have replaced it.

 

[Mark W]

Bad ground.


Mark...