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Discussion Starter · #1 ·
The trailer lights on my pickup appear to be factory and I was having issues today when I was testing my lighting on my trailer. The trailer lights are all wired correctly as my neighbors truck tested it and it is good. When I hook up mine the left turn signal is not working at all. I tracked the yellow wire down and from the plug towards the dash is a black plastic box with a yellow and also a green wire going into it and a green, yellow and red coming out going towards the dash. The yellow wire has weak voltage on the plug side and a strong voltage on the dash side. This box is causing the droppage. What is this box? It is black and about 4"x3"X.5". I don't want to take it out because it must be doing something? Please help because I am tempted to bypass this by taking it out but that extra red wire is going in it. Green is right turn signal and yellow is left turn signal. Thanks.
 

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Soylent Green sales
rock crawler
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12,801 Posts
If your trailer connector is the 4-pin type, that box would be the converter.
Toyotas use one bulb for the turn signal and a 2 filament bulb for brake and tail light.
Most trailers just use a 2 filament bulb for all 3 functions.
The converter box makes it possible to combine the 2 bulbs into one. (All that's in it are 4 diodes - 2 for L and 2 for R). A diode has a small voltage drop (about 0.7V).
 

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Discussion Starter · #3 ·
So would it be safe to remove this box completely or do I need to leave it in? I did jump the green wire and it seems to work right for the right turn signal but now on the way to work my blinker acted like it was going out because it would stay on sometimes after I would make the turn. What is the red wire used for? I know the green is right and the yellow is left. I would really like to take this out because I think the converter is bad because it is causing too much voltage drop to light it up. Thanks!!
 

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Soylent Green sales
rock crawler
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I would make sure the ground (white) wire on both sides (vehicle and trailer) is clean and tight first. It could be that easy.
 
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