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Turn signal not working properly

Rodd

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My Rear right hand turn signal (on my suburban)works fine with the lights off however with the lights on, it blinks fast at the front and rear. I noticed that the top tail light doesn't light up when the lights are one while the left side both top and bottom light up. I took the working light assembly off my 95 sierra and tried it on the suburban and got the same results. This tells me that it is in the pigtail/plug somewhere. I am thinking of clipping it and splicing in a new one but not sure if there is a way to trace the tail light pigtail.
 

schiker

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If you try to probe the pigtail for those lights use an actual bulb to draw current with the headlights on (get the same bulb and makeup "jumpers" or test wires). It sounds like there is a connection that is marginal. It works with low current but with high current of all the lights it has high resistance and not allowing current to flow and the quick flash is indicating a bulb is blown. A normal test light or multi meter here would probably give false ok's. Grounds are always important and may look at your trailer wiring if there is a short there might draw just a little current to reveal the marginal connection.
 

Rodd

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If you try to probe the pigtail for those lights use an actual bulb to draw current with the headlights on (get the same bulb and makeup "jumpers" or test wires). It sounds like there is a connection that is marginal. It works with low current but with high current of all the lights it has high resistance and not allowing current to flow and the quick flash is indicating a bulb is blown. A normal test light or multi meter here would probably give false ok's. Grounds are always important and may look at your trailer wiring if there is a short there might draw just a little current to reveal the marginal connection.
So you think it could be in the tow wiring? That is easy to check for open wires or anomalies visually. If there is nothing plugged into the tow wiring how can it cause a problem with the regular wiring?
 

schiker

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It's just a possibility. I had a loose wire in my trailer plug that back fed through my reverse lights and caused me a problem (the truck did not cut off with key off). The frame is basically a big busbar and there are several shared nodes in different wiring circuits.

What it sounds like you might be having a problem is when a lot of current is flowing through the grounds of the lights its causing higher resistance so that the bulb isn't working but when the lights are off the blinker works fine.

I have been fooled looking for marginal connections using a DMM and test light so suggest using a test bulb that will actually pull enough current to test the wiring.
 

Rodd

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After dealing with these tail light gremmlins for over a year I decided to replace the tail light wiring harness. Now that is done the parking lights don't work with the light switch on. I checked the fuses that I think might correlate to it and all of them are good. Does anyone know what fuse / fuses correlate to the parking lights?
 

Will L.

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idk the fuse locations, need to look that and a full schematic up in a manual. Sounds like the connection at the neww harness is faulty adding to the problem.
All connections need to be removed, cleaned and tightened.

There is likely a bad ground or bad connection in the running light/ head lights circuit. then because that has a higher amperage draw it is picking up it's ground through the turn signal circuit via the bulb.

It is possible the turn signal switch, headlight switch, emergency flasher switch could cause it also. But don't just swap parts because like when you changed the harness, if it isn't the problem it can just add a new one complicating it more. This is why the schematic is important so you can follow each section of the circuit and test the functions of the switches properly.
 

Husker6.5

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Do you have a trailer wiring harness on your vehicle? I have seen the type (regardless of brand) that uses the T-tap type connectors to splice into the wiring harness cause much the same symptoms that you describe. Over the years, the tap causes the harness wiring to corrode and either become much more resistive or corrode through completely and cause an open circuit. That can lead to all sorts of things, like one circuit grounding back through another, non-operating lights or only one side working, etc.
 

Husker6.5

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The best type of trailer harness are the ones that plug in in-line with the factory harness connectors for each taillight assembly to tap power for the trailer harness.
 

Will L.

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We call those “scotch lock taps connectors” because scotch invented them pieces of dung.
Those are very useful in certain situations. Like you hate someone so you put them on their truck harness.
Or your trash can is 3/4 full and you want to fill it the rest of the way.
 
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