Electrical Jeep Lights When Being Towed
TSB8C
Old Time Jeeper
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- 1984 CJ7, 420 HP "ZZ6 EFI" Crate engine, 700R4, D300, Dana30 front, Dana489 rear, 4.56 gears, 4" lift
So I flat-tow my CJ from time to time and have always wanted the Jeep's lights to act like trailer lights when it is being towed. This was an easy add-on/mod and very cheap to do (about $25). I have a tow bar that connects to the d-ring mounts on my front bumper. So the actual towing is easy. But I wanted the lights to work also. So I purchased three items from Amazon. First, a 60" 4-wire extension cable to attach to the tow bar itself. This has a standard trailer 4-wire plug on each end, one being the "vehicle side" and one being the "trailer side" type plugs. With this I can plug it into the trailer light plug on the vehicle I am towing with and then plug the other end into a plug mounted on the Jeep and wired into the Jeep's harness. The second item was a standard trailer wiring kit. This is about 10' of wire and a "trailer side" 4-wire plug on it. You would normally use this to wire up your own trailer lights. Since I was wiring up the Jeep lights to act like a trailer, this was perfect. The third item was a mounting bracket to attach the plug on the Jeep's front bumper. You could leave the plug hanging, or tuck it up somewhere when not in use. But I wanted a permanent mounting option. This is a clamp style mount that sandwiches the plug and has two holes for mounting it.
Next step was to mount the plug onto the Jeep's front bumper. I built my bumper myself from some round pipe and didn't want to try and mount this flat clamp to a round surface. So I used the "lip" at the front of my winch mounting plate instead. A perfect flat surface just the right size.
Now to route the wires. There are 4 wires: (1) Ground, (2) Running lights, (3) Left brake/blinker, (4) Right braker/blinker. I ran the wires under my winch mounting plate, up the side of the radiator and along-side the other headlight and blinker wiring harness. then out the opening in the side of the front grill and along the inner fender well where the other wires and the horn were already mounted.
Now the connections. The ground can go anywhere you have a solid ground connection. The running light wire can connect to any existing light's running light connection. Front and rear are all hooked together. The left and right brake/blinker wires need to connect to the rear wiring of the Jeep. The front and rear blinkers are NOT tied together. So you can't just tie into the front blinkers and have rear lights working. So I mounted the ground to an existing lug in the engine compartment. The other three wires I ran in through the firewall by drilling a hole and installing a grommet in my block-off plate covering the hole where the clutch lever used to be before I installed the auto Transmission . Then and up under the dash where the existing connector is near the fuse box that has the wiring harness connector. This is the connecter behind the e-brake lever where you have a 6-pin connector for the fuel sending unit, rear running lights, left and right rear brake/blinker, and reverse lights. The solid white wire in the connector is the rear running lights. The white with black stripe is the reverse lights (don't tie into that one). The lighter green wire is the right brake/blinker and the darker green with a black stripe is the left brake/blinker. And of course the pink is your fuel level sending unit, so leave that one alone as well.
With all the wires connected, there is one more issue to address. Your rear brake/blinker lights are tied together through the blinker switch in the column. When the blinker is off, you can hit the brake pedal and both lights come on together (left and right). It's only when you turn on the blinker by moving the lever up or down that the switch inside the column separates that circuit so that now the left and the right are no longer tied together. So as long as the blinker switch is not on (sitting in the normal centered position) both rear lights will come on together whenever the vehicle you are towing with tries to use either blinker. So you need a way to keep these two circuits separated while being towed. Now you could just hit the blinker lever up or down when you're going to tow the Jeep. But as soon as the steering wheel turns and then turns back, it will turn off the blinker and re-center the lever. So you need an electrical way to isolate the two rear circuits. Now they make diode packs and harnesses that do this. Using a set of diodes between the two circuits will prevent current from one side from flowing into the other through your blinker switch. But I like doing stuff myself and it's easy to do. You simply need to cut one of the wires going to either rear blinker light and connect it through a switch. Now you can leave the switch on for normal driving and the circuit works like normal, or turn the switch off to disconnect the one circuit from the blinker switch. Now the two sides will be separated and no issue of current flowing from one to the other. You basically have a "being towed" mode switch. I already had a couple of switches on my dash for the dual battery isolator, front fog lights, and the OBA setup. I also already had another switch that matched the existing ones. So I just popped another one in there and wired it up into the connector for the blinkers at the base of the column. Doesn't matter whether you splice into the left or the right. Either one does the job. Be sure to wire into the Jeep harness side of the connector rather than the wires coming down the column from the switch. That way you can change your blinker switch in the future if needed.
Now to connect it all up.
Keep in mind that this is not a workable solution if you have an older Jeep you're going to be towing that has a 6V system if the towing vehicle has a 12V. You don't want to send 12V into your older 6V system. But now when I want to tow the Jeep, just connect the two bar, plug in the lighting wires like any other trailer lights, and flip the dash switch. Also note: I previously removed the steering wheel lock "plunger" in my column when I did the push button start. Since I no longer use the keyed ignition on the column, my steering wheel can spin freely, which works when being towed as well.
Next step was to mount the plug onto the Jeep's front bumper. I built my bumper myself from some round pipe and didn't want to try and mount this flat clamp to a round surface. So I used the "lip" at the front of my winch mounting plate instead. A perfect flat surface just the right size.
Now to route the wires. There are 4 wires: (1) Ground, (2) Running lights, (3) Left brake/blinker, (4) Right braker/blinker. I ran the wires under my winch mounting plate, up the side of the radiator and along-side the other headlight and blinker wiring harness. then out the opening in the side of the front grill and along the inner fender well where the other wires and the horn were already mounted.
Now the connections. The ground can go anywhere you have a solid ground connection. The running light wire can connect to any existing light's running light connection. Front and rear are all hooked together. The left and right brake/blinker wires need to connect to the rear wiring of the Jeep. The front and rear blinkers are NOT tied together. So you can't just tie into the front blinkers and have rear lights working. So I mounted the ground to an existing lug in the engine compartment. The other three wires I ran in through the firewall by drilling a hole and installing a grommet in my block-off plate covering the hole where the clutch lever used to be before I installed the auto Transmission . Then and up under the dash where the existing connector is near the fuse box that has the wiring harness connector. This is the connecter behind the e-brake lever where you have a 6-pin connector for the fuel sending unit, rear running lights, left and right rear brake/blinker, and reverse lights. The solid white wire in the connector is the rear running lights. The white with black stripe is the reverse lights (don't tie into that one). The lighter green wire is the right brake/blinker and the darker green with a black stripe is the left brake/blinker. And of course the pink is your fuel level sending unit, so leave that one alone as well.
With all the wires connected, there is one more issue to address. Your rear brake/blinker lights are tied together through the blinker switch in the column. When the blinker is off, you can hit the brake pedal and both lights come on together (left and right). It's only when you turn on the blinker by moving the lever up or down that the switch inside the column separates that circuit so that now the left and the right are no longer tied together. So as long as the blinker switch is not on (sitting in the normal centered position) both rear lights will come on together whenever the vehicle you are towing with tries to use either blinker. So you need a way to keep these two circuits separated while being towed. Now you could just hit the blinker lever up or down when you're going to tow the Jeep. But as soon as the steering wheel turns and then turns back, it will turn off the blinker and re-center the lever. So you need an electrical way to isolate the two rear circuits. Now they make diode packs and harnesses that do this. Using a set of diodes between the two circuits will prevent current from one side from flowing into the other through your blinker switch. But I like doing stuff myself and it's easy to do. You simply need to cut one of the wires going to either rear blinker light and connect it through a switch. Now you can leave the switch on for normal driving and the circuit works like normal, or turn the switch off to disconnect the one circuit from the blinker switch. Now the two sides will be separated and no issue of current flowing from one to the other. You basically have a "being towed" mode switch. I already had a couple of switches on my dash for the dual battery isolator, front fog lights, and the OBA setup. I also already had another switch that matched the existing ones. So I just popped another one in there and wired it up into the connector for the blinkers at the base of the column. Doesn't matter whether you splice into the left or the right. Either one does the job. Be sure to wire into the Jeep harness side of the connector rather than the wires coming down the column from the switch. That way you can change your blinker switch in the future if needed.
Now to connect it all up.
Keep in mind that this is not a workable solution if you have an older Jeep you're going to be towing that has a 6V system if the towing vehicle has a 12V. You don't want to send 12V into your older 6V system. But now when I want to tow the Jeep, just connect the two bar, plug in the lighting wires like any other trailer lights, and flip the dash switch. Also note: I previously removed the steering wheel lock "plunger" in my column when I did the push button start. Since I no longer use the keyed ignition on the column, my steering wheel can spin freely, which works when being towed as well.
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