Wiring a trailer power wire/reverse light?

I have an expo trailer and want to run a wire through mytrailer harness from my truck that I can use to charge the battery in the trailer while I am driving. I also want to run a power wire to my 55watt halogen back-up light on the trailer that is activated when I put the truck in reverse. My truck has the 7 way plug as well as the trailer. I just don't know how to wire the thing right. I'm sure relays will be involved. Blessings

Here is a diagram of the seven pin plug: http://www.google.com/imgres?imgurl...a=X&ei=N3BZUPW9M-KWiAKMl4GgAw&ved=0CC8Q9QEwAg

Wire the backup light through the "aux" terminal. There is more than one way to wire the charge system. Mine is truck battery >> 30 amp breaker >> 12V continous duty starter relay >> trailer plug >> trailer battery. I use 10ga wire. You'll need the ground circuit too. The relay is triggered when the ignition is on using a wire from the fuse box under the hood. Some people use a battery isolator in place of the relay, but the relay has always worked well for me.

Is that middle pin from the truck already hot or do I need to run a wirre from the battery to make it hot?

If you have the tow package on your vehicle it should be hooked up, take a volt meter or test light to find out. . With the key or ignition off there should be no power to the middle pin, start the vehicle and check for 12v, if the meter shows 12v or the test light comes on your in like Flynn and good to go.

wingysataday said:

Is that middle pin from the truck already hot or do I need to run a wirre from the battery to make it hot?

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The center terminal may already be wired for backup. The only way to know is to put the truck in reverse, key on, and see if that produces 12V on that pin. If not you will have to wire it.

If you want the backup lights on the trailer to come on in reverse then connect a backup light wire to the middle truck terminal, then wire the trailer side to the trailer flood light. You could also run a separate circuit with a switch on the dash if you don't want the flood activated with reverse. Does that make sense?

On my trailer I have 2 55 watt flood lights. I also have high powered backup lights in the truck. I did not want to power all thoose lights from the factory harness. What I did was use a lead from the back light wire in the truck to trigger a small 30A Bosch type 4 pin relay. The relay was powered from the battery. That wire went through the center terminal and out to the flood lights. Basically, when the truck is in reverse the Bosch relay is triggered, sending power to the flood lights.

My truck came with the factory tow pkg. I tried to hook up the flood light on the trailer directly to the wiring harness and it just blows the fuse in the truck. DOWNHILL you mentioned running power to the bosch relay from a battery, where is this battery? in the truck or on the trailer? I also want to run a power wire to the battery tender in the trailer so when I am driving I can charge that battery. I want to be able to have the flood light on the trailer power independantly of the battery that is on the trailer. http://www.etrailer.com/faq-wiring.aspx. It looks like the middle connector is the reverse light and the black wire is a constant 12volts. I can use the black wire to power my battery tender and also go through a relay that will power my flood light on the trailer that is excited somehow when put in reverse?

wingysataday said:

My truck came with the factory tow pkg. I tried to hook up the flood light on the trailer directly to the wiring harness and it just blows the fuse in the truck. Most likely its because the total draw of the lights is too much for that circuit. You will need a relay as I described. The existing wire in the center position should be from the backup light right? Use that to trigger the relay instead. On the power side of the relay run one end to the truck battery or some other capable ignition on power source. The other end goes to the vacated center terminal on the truck. DOWNHILL you mentioned running power to the bosch relay from a battery, where is this battery? I used my truck battery, but you could also put the relay in the trailer and use the trailer battery to power the lightsin the truck or on the trailer? I also want to run a power wire to the battery tender in the trailer so when I am driving I can charge that battery. I want to be able to have the flood light on the trailer power independantly of the battery that is on the trailer. then use the scheme I described using the bosch relay on the truckhttp://www.etrailer.com/faq-wiring.aspx. It looks like the middle connector is the reverse light and the black wire is a constant 12volts. correct, the black wire is designed to charge the battery but you do not need a battery tender/charger. It is wired direct to the battery. A tender/charger is a 115 volt device designed to charge the battery from shore powerI can use the black wire to power my battery tender and also go through a relay that will power my flood light on the trailer that is excited somehow when put in reverse? yes

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May I suggest replacing the 55 watt back up light with an LED light. The power requirements are much lower, and the wire size smaller.

The battery tender is a 110v battery charger and would have to be wired up to a shore plug for power supply via an extension cord. When driving you can charge the batteries via the 12 volt supply from the 7 pin on the vehicle.

The center pin is for the reverse light. It may or may not be wired up. If it is not you need to connect it to the wiring for your reverse lights.

If you understand 12 volt DC wiring it's an easy task. If you don't understand 12 volt DC, and reading the wiring diagram is difficult, pay someone to do the work.

I can handle I think. I am just not savvy with the relay stuff. Does the relay come with a wiring diagram? I bought a couple H4 LED's off ebay and have not been able to get them to work. I think I might have some wiring issues in the plug. I think my reverse light wire has to much load on it since I did the reverse light mod on my truck taillights. I need to probably use the black wire from the 7 plug to run into the relay that is excited by the purple wire. I will also splice the black wire over to the battery in my trailer as well.
What gauge is the black wire coming from the truck harness? I will just match it on the trailer side.

wingysataday said:

I can handle I think. I am just not savvy with the relay stuff. Does the relay come with a wiring diagram? I bought a couple H4 LED's off ebay and have not been able to get them to work. I think I might have some wiring issues in the plug. I think my reverse light wire has to much load on it since I did the reverse light mod on my truck taillights. I need to probably use the black wire from the 7 plug to run into the relay that is excited by the purple wire. I will also splice the black wire over to the battery in my trailer as well.
What gauge is the black wire coming from the truck harness? I will just match it on the trailer side.

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If you did the backup light mod you definitely need a relay! That is why you are blowing fuses. The backup mod maxs out the stock wiring. You can power both the trailer light and the charge circuit for the trailer from the black wire on the truck plug, yes. Run an 18ga to 16ga wire through the relay to the light and 10ga to the battery. Be careful that the connections you make for these wires are good. A poor connection will result in a voltage drop that will affect charging efficiency. I would not use 3M wire splices for this. You want to use 10ga for the battery charge line to also minimize voltage drop. It doesn't matter what the truck wiring has.

LEDs are polarity sensitive. Most of the time when an LED light doesn't work it's because the leads ae reversed. I have heard that some LEDs can be fried by hooking them up in reverse. The ones that I have screwed up were all fine.

As for the relay, most of them have the diagram on the relay itself. These relays come in both a 4 pin version and a 5 pin version. All of them use standardized terminal numbers written on the relay, so I will give you the connections to use. Terminal 30 gets wired to the black wire circuit with(18-16ga). Purple wire gets removed from the truck plug and goes to terminal 85. Terminal 86 goes to ground (18ga). terminal 87 goes out to the trailer light (18-16ga) via the middle plug terminal where you removed the purple wire. If you bought a 5 pin relay you will also see an 87A terminal. You won't need that, so just ignore it. It is to power a second circuit like perhaps an indicator light on the dash.

terminal 30 = main power in (high amperage side)
terminal 87 (87A)= main power out to the driven device(s) (a light in this case) (high amperage side)
terminal 85 = trigger wire in (low amperage)
terminal 86 = ground for trigger current (low amperage)
**terminal 85 and 86 are not polarity sensitive so they can be reversed

I hope this helps and doesn't just make it more confusing. It's hard to know when you answer these questions how much the OP knows coming in.

downhill, very helpful thank you. Where do I put this relay? Is it on the trailer side somewhere on the tongue or in my trailer battery box? If the truck side black wire is only 20 gauge wire than why put a 10g on the trailer side, seems wasteful?

Your 12V charge wire is 20 ga?? Generally the minimum is 12ga. Maybe Toyota is using another color. Generally, black is 12V, white is ground, blue is brakes. All of these should be 12ga minimum. I wired my own truck and I used 10ga. I think you might be better off getting someone local to help you out with this. They can look at what you have and make sure you aren't creating something hazardous. No offense meant, but I get the feeling you don't understand well enough to tackle this without help. I'd hate to encourage you to do something that might end up causing a fire, or other costly repairs.

The reason I suggested 10ga is because during the initial charging of a dead battery the current can get pretty high. The other reason is that charging efficiency is dependent on the volatge reaching the battery. The greater the voltage differential between charger and battery (within reason), the more efficient the charge function. That is why alternators are regulated at around 14 volts even though a fully charged battery is just 12.7 volts. There is a long wire run to a trailer battery, so there can be substantial voltage drop over that distance unless a larger wire is used.