Trailer Wiring

hearnc843 · Jan 10, 2021

I recently purchased a horse trailer with some questionable wiring, and I am going through everything.
This might be a rookie question- but when I wire up the left and right turn signals, will those bulbs also function as brake/running lights? As in, when I turn on the running lights on my vehicle will the rear tail lights come on? And when I brake, will these tail lights also turn brighter red?

mhb@ufe · Jan 10, 2021

Wiring the directional lights will take care of the brake lights but the running lights are on a separate wire.

Mark

dpendzic · Jan 10, 2021

you need a 2 element bulb to have running lights and directional lights from the same bulb---and of course separate wire feeds

rustred · Jan 10, 2021

Yellow wire is left signal , green right signal and brown is tail lights that’s if you have color coded wires on it. Depends on the trailers age but those bulbs need to be #1157 with 2 filaments. The newer push in bulbs are a diff number.

bc · Jan 10, 2021

(quoted from post at 20:46:38 01/10/21) I recently purchased a horse trailer with some questionable wiring, and I am going through everything.
This might be a rookie question- but when I wire up the left and right turn signals, will those bulbs also function as brake/running lights? As in, when I turn on the running lights on my vehicle will the rear tail lights come on? And when I brake, will these tail lights also turn brighter red?

Yes, that is correct. Although I have seen them get the wires reversed/switched to where the brighter/larger brake filament on the 1157 bulb would come on with the taillights and the dimmer/smaller taillight filament on the 1157 coming on with the brakes.

used red MN · Jan 10, 2021

Hope I am not to late, if you wired by the color of the wires rustred gave it is correct and those are the colors you will find in most GM wiring at least prior to 1990. Sorry, bc but the explanation you gave is NEARLY correct. The brighter element in the 1157 dual element bulb is the the stop and turn, which are green right and yellow left. The power from the stop light switch when activate goes up through the switch in the steering column and when no turn signal is selected back out to the bright filament of the tail light. When a turn is selected contacts in the column direcect the wire to the bright tail light filament to be powered by the flasher circuit thus interrupting the steady on bright filament ..brake.. on the selected turn side to flash. The dimmer filament is simply the tail light or running light circuit which is the brown wire. Sometimes you would see were the bright filament was wired as the constant on tail light and in some later models that used plastic housings and sockets could melt from the higher heat produced. I could go on to explain how front vehicle turn signals with side fender lights were wired to be both a turn and side marker with a single element bulb, but that would be much easier if you were here with me so I could draw a circuit diagram. Oh I should add if you are towing with a newer model or foreign vehicle they may have a 4 circuit tail light system. This means there is a circuit for right turn, left turn, brake and tail. Meaning each side tail light needs 3 elements, a change added mostly due to the addition of the third center brake light. You will need a converter that electronically converts that vehicle wiring to match the older wiring of your trailer.

Steve@Advance · Jan 10, 2021

Yes, that is correct.

As long as the vehicle is wired to operate the lights that way, and most are.

Some that have separate turn signals from brake lights require a converter box to operate trailer lights.

Trailer wiring takes a beating. I use soldered and shrink tube connections sealed with liquid electric tape, keep everything well supported and tucked up tight. You will have much longer trouble free life with sealed LED lights.

used red MN · Jan 10, 2021

Oops, sorry bc you were correct! I missed the part where you said ..I have seen them get the wires reversed.. my bad!!

bc · Jan 10, 2021

(quoted from post at 00:24:59 01/11/21) Oops, sorry bc you were correct! I missed the part where you said ..I have seen them get the wires reversed.. my bad!!

That's ok. I've seen them get reversed because it was me that did it. It's easy to miss in the day light but at night the error shows up better. Got about 4 trailers that I'm waiting on the price of LEDs to come down. The vehicles and trailers with the 1157 bulbs are getting harder for me to see as I get older.

used red MN · Jan 11, 2021

Should also add that the part about needing a converter for the 4 circuit system really doesn’t apply to your post. That would only come into play if you were doing wiring on the plug in the vehicle. If installed correctly the existing plug in a vehicle should be wired to compensate for this. Really wish we could edit posts here.

showcrop · Jan 11, 2021

Do yourself a favor and get a new harness and lights with modern water proof connections. They are not that expensive.

RJKeith · Jan 11, 2021

Most taillight bulbs have two filaments. one for the normal taillight and one for the turn/break light, so you will run two wires to each tail light, with the trailer chasse as the common.

Carlmac 369 · Jan 11, 2021

(quoted from post at 02:16:09 01/11/21) Hope I am not to late, if you wired by the color of the wires rustred gave it is correct and those are the colors you will find in most GM wiring at least prior to 1990. Sorry, bc but the explanation you gave is NEARLY correct. The brighter element in the 1157 dual element bulb is the the stop and turn, which are green right and yellow left. The power from the stop light switch when activate goes up through the switch in the steering column and when no turn signal is selected back out to the bright filament of the tail light. When a turn is selected contacts in the column direcect the wire to the bright tail light filament to be powered by the flasher circuit thus interrupting the steady on bright filament ..brake.. on the selected turn side to flash. The dimmer filament is simply the tail light or running light circuit which is the brown wire. Sometimes you would see were the bright filament was wired as the constant on tail light and in some later models that used plastic housings and sockets could melt from the higher heat produced. I could go on to explain how front vehicle turn signals with side fender lights were wired to be both a turn and side marker with a single element bulb, but that would be much easier if you were here with me so I could draw a circuit diagram. Oh I should add if you are towing with a newer model or foreign vehicle they may have a 4 circuit tail light system. This means there is a circuit for right turn, left turn, brake and tail. Meaning each side tail light needs 3 elements, a change added mostly due to the addition of the third center brake light. You will need a converter that electronically converts that vehicle wiring to match the older wiring of your trailer.

Very well covered, although someone new to automotive electrical systems may have to spend some time absorbing it which is recommended.

A previous post mentioned not knowing the number for the newer push in equivalent of a 1157 bulb. That would be a 3157.

There is also a 4157. The 3157 and 4157 are different only in their longevity. The 4000 series is a new bulb containing Krypton gases and apparently have up to 4 times the longevity of the 3000 equivalents.

rustred · Jan 11, 2021

Yellow wire is left signal , green right signal and brown is tail lights that’s if you have color coded wires on it. Depends on the trailers age but those bulbs need to be #1157 with 2 filaments. The newer push in bulbs are a diff number.

bc · Jan 11, 2021

There is also a 4157. The 3157 and 4157 are different only in their longevity. The 4000 series is a new bulb containing Krypton gases and apparently have up to 4 times the longevity of the 3000 equivalents.

Are the 3157 and 4157 any brighter? Thanks.

Loosehandle · Jan 11, 2021

Watch out for mice chewing new wires if it has soy insolation

Carlmac 369 · Jan 11, 2021

(quoted from post at 12:54:46 01/11/21)

There is also a 4157. [b:95ecc7befe]The 3157 and 4157 are different only in their longevity. [/b:95ecc7befe]The 4000 series is a new bulb containing Krypton gases and apparently have up to 4 times the longevity of the 3000 equivalents.

Click to expand...

Are the 3157 and 4157 any brighter? Thanks.

Nope.

JimKS · Jan 11, 2021

number 1 thing to do when working on trailer wiring is to have the trailer hitch and safety chains UNHOOKED. I have seen people work hours because of poor ground in the harness.

Carlmac 369 · Jan 11, 2021

(quoted from post at 15:59:14 01/11/21) number 1 thing to do when working on trailer wiring is to have the trailer hitch and safety chains UNHOOKED. I have seen people work hours because of poor ground in the harness.

Yep. Running a dedicated ground to each lamp is a good practice as well.

Trailer Wiring

hearnc843

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mhb@ufe

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dpendzic

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rustred

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bc

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used red MN

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Steve@Advance

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used red MN

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bc

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used red MN

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showcrop

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RJKeith

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Carlmac 369

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rustred

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bc

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Loosehandle

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Carlmac 369

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JimKS

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Carlmac 369

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