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Ridgerunnerras, Auto Mechanic
Category: Car
Satisfied Customers: 602
Experience:  I have been fixing cars for 26 years for myself and at a used Car dealer. I am skill mechnical and autobody and paint repair
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I have a hudson utility trailer with brakes. I recently

Customer Question

I have a hudson utility trailer with brakes. I recently replaced the 7 way plug on the tow vehicle side and the trailer side along with a new brake-away switch and side marker and tail light. Bad grounds on the tail and side marker so I cleaned the rust off and put new lights and worked great, however, the brake lights and turn signal lights don't work at the same time. All the lights work, but turn and brake at the same time do not. Only the brake light lights up, no turn signal. Any suggestions? thank you
Submitted: 5 years ago.
Category: Car
Expert:  Auto_Enlightenment replied 5 years ago.
Auto_Enlightenment :

I will do my best to help. Please refrain from rating me until you are satisified. If you need more then please continue our conversation rather than rating me negatively. If I am unable to help then I will opt-out to see if another expert can help.

It sounds like you may have a single filiment bulb where a dual filiment bulb should be. Are the lights wired up for dual filiment bulbs and is a dual filiment bulb installed in the light?

Customer :

both tail lights are designed for dual filaments and both have dual filament bulbs. i did notice, however, that it only does this when the headlights on tow vehicle are on. so for the problem to appear headlights on, brakes on, and then turn signal does not work.

Auto_Enlightenment :

On your tow vehicle, are the turn signals and brake lights seperate? If so, you will need to wire up a seperate converter which uses diodes to change the current to your one piece trailer lights. Click Here for an example This will convert the vehicles 3 wire system to the trailers 2 wire system.

Auto_Enlightenment :

If you already have one of these, I would check it to see if it is swollen and bulging out. I've seen these fail many times and they usually bulge out from overheating.

Customer :

tow vehicle doesnt have separate turn signals. it was working fine for a number of years until recently. could a bad ground cause this to happen?

Auto_Enlightenment :

I imagine if you had a bad ground the lights wouldn't work at all. Did you always have the break away and 7 way plug or are these new additions?

Customer :

always had them

Auto_Enlightenment :

I'm thinking, please bare with me. Thanks.

Customer :

no problem

Auto_Enlightenment :

Do you have a digital volt meter? Let's try this. You could have the brown(running lights) wire shorting out on the turn signals wire. The brown wire only gets power when the headlights are on. If there is a short then when the headlights are turned on then the short would kill the turn signals.This should also affect the brake lights but who knows, it's worth checking out. If you have a digital meter then set it to read continuity/ohms Ω. Place one lead on the brown wire and the other on the turn/stop wires(green & yellow) to see if there is continuity(there should not be). Do this for each side(tow vehicle & trailer) seperately to see what the results are.

If this does not reveal anything then lets hook the connectors up with the trailer seperated from the tow vehiicle to see how the lights behave. This can rule out any crazy ground problems. If the lights work properly then the grounds are good.

Customer :

I found the problem. The tail lights were wired backwards, so the stronger filament was receiving the running light and the weaker filament was receiving the brake signal. It is so sunny outside it took me putting my hands over the light to be able to see the faint blinking of the turn signal. another problem, however, did arise. I replaced my magnets and resurfaced the drums, and replaced the break away and battery, but the break away does not work when connected to the hitch. For example, you can actually here the magnets hit the drum when the break away is pulled, but you cannot here the magnets hit when connected to the tow vehicle. When on the jack, I cannot move the brake axle wheel by hand when the break away is pulled, so i know they are working but only when the trailer is not connected to the vehicle. Nor do the breaks work when they are activated with the brake pedal. So it sounds like a ground issue, no? Thanks for any input

Expert:  Auto_Enlightenment replied 5 years ago.

I'm glad you got the lights working, that makes perfect sense.

So the brakes work only when you pull the break away with the trailer disconnected from the tow vehicles hitch and harness and at no other time?

Customer: replied 5 years ago.
well, I thought that was the case, but they just dont seem to work at all. i thought they worked when the trailer was disconnected from the vehicle because i could hear the magnets hit the drums when i pulled the break away out, but i was able to push the trailer from behind by hand, so I figured they couldn't be working. once again I replaced the shoes ( the correct way) new magnets rated for the axle, and had the drums resurfaced. The drums where nice and snug when I slid them back over the brake assembly, so the adjustment should be correct. I even checked to make sure the brake assemblies were correct for that axle and they where installed on the correct side. Any suggestions?
Expert:  Auto_Enlightenment replied 5 years ago.
The only thing I could suggest is to double check all of your wiring to make sure power and ground for the brakes is wired up correctly. Sometimes these types of problems can be hard to diagnose without being there to physically check things. I am going to opt out to see if another expert can help you with this.
Expert:  Ridgerunnerras replied 5 years ago.

Hello I would like to assist you with this.

As you well know by now trailer lights and break connections can be a royal pain in the rear.

First thing I want you to do is verified with a Voltmeter that you are getting full battery voltage (12v or better) to every output wire on your connector of your vehicle when it is supposed to be there.

So check your running lights, your turn signal lights, your brake lights, and your Trailer break wire.

You should also have a ground wire in your connector.Do not count on the ground circuit being completed through the trailer hitch.

Once you have verified that you're getting all of the correct voltages to the connector at the back of the vehicle with out the trailer connected, Then please connect the trailer wire harness to the vehicle .Do not connect the trailer hitch to the vehicle. I want the trailer physically disconnected and only have the wires connected.

Now check your lights and your break function and see if this differs from before.

If nothing works then you do not have the ground connection back to the vehicle battery.

If they still work as they did before go to each light and measure the voltage and make sure it is the same voltage is that you measured at the connector on the car.

Make sure that you have a physical ground wire connecting to the trailer frame and going through the connector back to the negative side of the battery.

Most trailer wiring problems are caused by A bad ground connection.

You can test your ground connection by using a volt ohm meter with this set on oHMs. Run a wire from the nagative side of the battery to your meter and then the other probe on the meter test it to the frame of the trailer. A perfect connection would be 0 ohms. But I would say anything under 100 OHMs would be OK .

Here's a wiring diagram of how the trailer wire should be wired

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