Wiring the truck for towing is fairly easy. There are a number of good wiring kits available and these should be used, rather than trying to design your own. All trailers will need brake lights, turn signals, tail lights and side marker lights. Most states require extra marker lights for overwide trailers. Also, most states have recently required back-up lights for trailers, and most trailer manufacturers have been building trailers with back-up lights for several years. Additionally, some Class I, most Class II and all Class III trailers will have electric brakes. Add to this number an accessories wire, to operate the trailer internal equipment or to charge the trailer's battery, and you can have as many as seven wires in the harness.
Determine the equipment on your trailer and buy the wiring kit necessary. The kit will contain all the wires needed, plus a plug adapter set which includes the female plug, mounted on the bumper or hitch, and the male plug, wired into, or plugged into the trailer harness. When installing the kit, follow the manufacturer's instructions. The color coding of the wires tends to be standard throughout the industry.
One point to note: some domestic vehicles and most imported vehicles, have separate turn signals. On most domestic vehicles, the brake lights and rear turn signals operate with the same bulb. For those vehicles with separate turn signals, you can purchase an isolation unit so that the brake lights won't blink whenever the turn signals are operated, or, you can go to your local electronics supply house and buy four diodes to wire in series with the brake and turn signal bulbs. Diodes will isolate the brake and turn signals. The choice is yours. The isolation units are simple and quick to install, but far more expensive than the diodes. The diodes, however, require more work to install properly, since they require the cutting of each bulb's wire and soldering in place of the diode.
A final point, the best kits are those with a spring loaded cover on the vehicle mounted socket. This cover prevents dirt and moisture from corroding the terminals. Never let the vehicle socket hang loosely; always mount it securely to the bumper or hitch.
The most common problem associated with trailer towing is engine overheating. With factory installed trailer towing packages, a heavy duty cooling system is usually included. Heavy duty cooling systems are available as optional equipment on most trucks, with or without a trailer package. If you have one of these extra capacity systems, you shouldn't have overheating problems.
If you have a standard cooling system, without an expansion tank, you'll definitely need to get an aftermarket expansion tank kit, preferably one with at least a 2 quart capacity. These kits are easily installed on the radiator's overflow hose, and come with a pressure cap designed for expansion tanks.
Another helpful accessory is a Flex Fan. These fans are large diameter units designed to provide more air flow at low speeds, with blades that have deeply cupped surfaces. The blades then flex, or flatten out, at high speed, when less cooling air is needed. These fans are far lighter in weight than stock fans, requiring less horsepower to drive them. Also, they are far quieter than stock fans. If you do decide to replace your stock fan with a flex fan, note that if your truck has a fan clutch, a spacer between the flex fan and water pump hub usually will be needed.
Aftermarket engine oil coolers are helpful for prolonging engine oil life and reducing overall engine temperatures. Both of these factors increase engine life. While not absolutely necessary in towing Class I and some Class II trailers, they are recommended for heavier Class II and all Class III towing.
Engine oil cooler systems consist of an adapter, screwed on in place of the oil filter, a remote filter mounting and a multi-tube, finned heat exchanger, which is mounted in front of the radiator or air conditioning condenser.Transmission
An automatic transmission is usually recommended for trailer towing. But the increased load of trailer towing causes an increase in the temperature of the automatic transmission fluid - heat is the worst enemy of an automatic transmission. As the temperature of the fluid increases, the life of the fluid decreases. It is essential, therefore, that you install an automatic transmission fluid cooler.
The cooler, which consists of a multi-tube, finned heat exchanger, is usually installed in front of the radiator or air conditioning compressor, and hooked inline with the transmission cooler tank inlet line. Follow the cooler manufacturer's installation instructions and select a cooler of at least adequate capacity, based upon the combined gross weights of the truck and trailer.
Cooler manufacturers recommend that you use an aftermarket cooler in addition to, and not instead of, the present cooling tank in your truck's radiator. If you do want to use it in place of the radiator cooling tank, get a cooler at least two sizes larger than normally necessary.
One note: A transmission cooler can sometimes cause slow or harsh shifting in the transmission until the fluid has a chance to come up to normal operating temperature. This condition is usually more pronounced in the winter months. Some coolers can be purchased or retrofitted with a temperature bypass valve which will allow fluid flow through the cooler only when the fluid has reached operating temperature.