BX8848 Installation Instructions
4 Diode Wiring Kit
For Motorhomes With Red Tail Lights
292-1305 Rev. D Page 1 of 5 4/11/12
WARNING: Incorrect wiring may result in blown fuses, damaged wiring, re, or bodily injury. Blue Ox
recommends installation of this kit by a trained professional. Blue Ox will not be responsible for any
personal property damage, or bodily injury caused by incorrect wiring or misuse of this product.
Note: Some motorhomes may have amber turn signals and red brake lights. Check the rear outlet
to see if the turn and brake signals are on one pin or spade. If they are not a converter is required to
change from a 5 wire to a 4 wire system.
1. Starting in the engine compartment of the towed vehicle, run the harness through the re wall, under the
drivers side door sill plate, under the back seat, and into the trunk area. Depending on the motorhome set
up, the wire at the front of the engine compartment should be wired into either a 4-wire or 6-wire trailer plug
that is mounted to the front of the towed vehicle.
2. Make sure that the white wire is grounded to the vehicle chassis. It is also important to have a good ground
on the towing vehicle.
Use a 12 Volt D.C. continuity lamp tester with a needle point prod to identify the “hot” wires which power
the brake and tail lights. Ground one end of tester, and insert prod through the insulation of each wire
to identify. At this point the 4-conductor cable should be cut to length, leaving enough slack to reach the
tail light connector. NOTE: Vehicle lights must be on and the corresponding turn signals will have to be
operating in order for wires to be “hot”.
3. After the tail light and turn signal wires are identied and marked, shut off the power then cut each wire.
Cut any excess wire off of the four wire harness. Leave about 6 to 8 inches of slack. Separate the four
wires. Start on the outside and carefully peel each wire back about 6 inches. Cut and strip each wire and
crimp a female spade terminal on each wire. Plug the green wire into the right brake diode block. Plug
the yellow wire into the left brake diode block. Plug the female terminal from the front of the car into the
“in” side of the tail light diode blocks and the female terminal from the rear of the car into the “out” side of
the diodes. Plug the brown wire from the four wire harness into the “in” side of the diode block (see wiring
diagram). Test the car tail lights to make sure they work.
4. The last part of the wiring is to ground the four wire harness. The white wire is the ground. In the engine
compartment nd a bolt near the wire harness that will provide a metal-to-metal contact. Carefully cut just
the white wire and peel back enough wire to reach the selected bolt. Strip and crimp the ring terminal on
the wire. Remove the bolt and place the ring terminal under it and tighten. NOTE: If you are installing a
4-wire or 6-wire trailer plug on the front of the towed vehicle, then you may insert the ground into one of
these terminals to provide a ground for the system.
5. Secure the four wire harness several places between the grill and the front of dash to keep the harness
from getting tangled up in moving parts or touching engine parts that will get hot.
6. Hook up the towing vehicle to the wire harness and test the installation by operating the tail lights, turn
signals and brake lights. If the wiring on the towing vehicle does not match, you will need to change either
the wires at trailer plug or on the towing vehicle to match.
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