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How To Light The Old Bomb

Most new tractors on the market today offer high-intensity lighting. In contrast, lights on older tractors can be pretty minimal, which makes pulling wide implements at night or feeding cattle after dark in the winter pretty frustrating.

Fortunately, installing extra lights on an older tractor is pretty easy. A lot of aftermarket lighting equipment is available, and most of it comes with a reasonable price tag. You can add just one or two lights or install a complete high-intensity lighting kit.

But this can also be an easy way to set the tractor on fire, especially if electrical connections aren’t made properly. So to help you upgrade your older tractor safely, here is a look at how to add lights, starting with the basics.

Understanding an electrical circuit is the first step. Photo 1 demonstrates the basic principle. Current flows from the battery’s positive terminal through the tester’s bulb and back to the negative terminal through the red wire. When the connection is complete, the circuit is “closed.” If the connection is broken anywhere, either before or after the bulb, the circuit is “open” and current won’t flow. The light stays out.

The mock up in photo 2 shows a simple lighting circuit. The metal bar substitutes for a tractor chassis. Current flows from the positive battery terminal to a fuse box. From there, it goes to a switch. If the switch is “closed,” current passes through it to the light. Inside the light, current passes through the bulb and out through the mounting bracket to the tractor’s chassis, then back to the negative (ground) battery terminal. This is exactly the same route as in photo 1.

Typically, automotive lights ground through their mounting base. But when installed on a fibreglass or plastic component, they can’t make a complete (closed) circuit. You can connect a ground wire from the mounting base to a metal component on the chassis to solve the problem.


Adding a lot of lights creates a high current (amperage) flow, so you’ll need a relay to keep high-current wires out of the cab or to shorten a long wire run. A relay is just a remotely controlled switch used to activate circuits.

The mock up in photo 3 shows how two circuits are required to make a relay work. The red wire shows the power circuit, which supplies current to the light. A second circuit (the green wire) is used to route a low current flow through the switch just to control the relay. When the switch is “closed” it allows current to flow through the relay’s control circuit. That closes the “normally open” relay and allows the power current to flow through the red wire directly to the light.

Many accessory lighting kits in the automotive aftermarket include a relay for this just this kind of connection.

To make sure all circuit components have an adequate rating, be sure to calculate the amperage flow through the circuit. To do that, check the watt output of each lamp, add them together and divide by 12 (for 12-volt systems) to get the amperage flow. Watts/ volts=amps.

Thicker wire is capable of carrying more current than thin wire. For a 20-amp circuit, 16 gauge wire is adequate for runs of up to 10 feet in length. To carry the same amount of current for lengths up to 15 feet, you’ll need 14-gauge wire. (Source: Haynes Techbook) Wire that is too small for the amperage load can overheat and cause a fire.


The easiest way to tap into battery power for extra lights is through an unused port on the tractor’s fuse box. However if that’s not an option, you can run a power lead directly to the positive terminal on the battery or to the “battery” connection on the starter, as shown in photo 4. But when connecting at the starter, be sure the tractor doesn’t start on 24 volts. If it does, the components in any 12-volt connection will burn out.

When connecting directly to battery power, be sure to route the connection through a line fuse, also shown in photo 4, but keep the fuse holder protected from the elements. The fuse will burn out if current flow (amperage) exceeds its capacity, protecting the circuit — and the tractor —from fire.

Finally, route all wires carefully and cut them to length, which avoids excess sagging. If possible, route them alongside existing wires and secure with cable ties. Don’t allow them to fray against metal edges. Shielding wires by running them inside a conduit, like the one in photo 5, prevents wires from rubbing or touching vibrating metal parts. Vibration can wear away the insulation on wires and cause them to ground on a metal surface. That can prevent the circuit from functioning and cause a fire.

When routing wires through openings in sheet metal, such as through a cab wall, install a rubber grommet first, even if the wires are inside a conduit. That isolates them from vibration damage.

Scott Garvey specializes in writing about tractors and farm machinery technology for publications in Canada and Great Britain. He’s also a former affiliate member of the Society of Automotive Engineers (SAE). He farms near Moosomin, Sask.

About the author


Scott Garvey

Scott Garvey is a freelance writer and video producer. He is also the former machinery editor at Grainews.



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