Step by step guide on how to troubleshoot and repair automotive tail and running lights, this information pertains to not working, dim and flickering lighting systems.
Begin with the car on level ground, engine off with the parking brake set, wear protective gloves and eye wear. When performing tests avoid connecting power wires or terminals to ground (metal), fuse damage can occur, most automotive bulb testing procedures are done in this manner.
Difficulty Scale: 4 of 10
Step 1 - Identify the light or lights that are non operational. If one tail light bulb has failed, the problem is probably the bulb itself or a bad connection, if all lights are non-operational, follow down the guide to Step 5.
Step 2 - Remove bulb socket to expose the bulb
for inspection, gently grasp the bulb and pull or push down and twist counterclockwise
to remove, some bulbs are accessible by removing the lens itself while other require
the removal of a plastic panel.
Step 3 - Remove the bulb and inspect, check for
any burned color or white with blue smoke inside the bulb which is an indication
of failure.
Step 4 - Replace the bulb with new and recheck
before re-installation.
Step 5 - If a new bulb still doesn't operate, use
a grounded testing light to help test power feeds to the bulb.
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Step 6 - With the bulb removed (optional) and while
the running lights are "ON", use a grounded test light to test the inner contacts
of the bulb socket or wire connectors. Be careful not to touch the test light lead
to the outer socket ring or to ground for this will cause a short circuit and fuse
failure.
Step 7 - A diagram will facilitate repairs but
is not needed for this test. Search
Google images or an online
service manual such as
Mitchell1 to obtain
a diagram.
Step 8 - After confirming power is present at the
socket, attach a pick or other pointy metal object to the test light clip, insert
both probe and pick into the ground and power terminals or wiring, this test confirms
power and ground at the socket.
Step 9 - Using an Exacto blade or sandpaper, scrape
clean the terminal connections that are inhibiting the electrical flow. Lighting
sockets are subject to heat and can melt plastic and cause corrosion which promotes
bulb operation failure, in severe cases the socket will need to be replaced.
Step 10 - If all running or tail lights are not
working, a fuse is used to protect the lighting system from overload and short circuits,
anytime more than one light bulb is out, the fuse is the first place to check, these
fuses are located in the power distribution center (pdc).
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Step 11 - A tail light control relay is used to
help shoulder the electrical draw many bulbs can cause on a single circuit, this
task is carried out by the BCM (body control module). The headlight/running light
switch is used as the trigger circuit which sends a signal to activate the relay.
When this relay fails, it will hinder the operation of the running lights.
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Step 12 - Next, remove the headlight switch to
probe harness wires, the test light must be connected to positive power such as
the battery which is needed to test ground circuit connections. Observe the test
light while operating the switch, the light should follow the switch operation.
On older cars, the switch controls headlight and tail light power, instead of grounding
BCM triggers. For these systems use a grounded test light and test for twelve volts
at the rear of the headlight switch connector (removed) on one or two of the terminals
or wires. If no power is confirmed, repair the fuse holder or the power feed (maxifuse
- fusible) from the fuse panel to the switch. If power is confirmed at the rear
of the switch, turn the switch to the "ON" position and test the remaining terminals
(or wires), power should be present at the remaining terminals.
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Step 13 - Diagram of a typical grounding BCM trigger
system, each vehicle will vary. Wiring diagrams are obtainable at
Google images or
Mitchell1
Step 14 - For final testing, a wiring diagram is
needed to trace wires to be tested in the lighting circuit, with the switch in the
"ON" position test for power output by probing lighting circuit wires which also
tests the BCM operation.
Step 15 - A dim light is caused by a poor ground
circuit which causes the electrical flow to back feed resulting in higher than usual
resistance. While the tail light bulb is installed, touch a grounded test light
to the outer ring or ground wire of the bulb socket. If the bulb brightness increases,
the bulb socket ground has gone open and must be cleaned or repaired-replaced.