How to repair dimmer switch? - 1986 Chevrolet Chevy

Instrument Panel Lamps Inoperative
Step
Action
Yes
No
1
Did you perform the Lighting System Diagnostic System Check?
YES - Go to Step 2
NO - Go to Diagnostic System Check - Lighting Systems in Lighting Systems.
2
Turn the ignition to the ON position.
Turn the headlamp switch to the ON position.
Turn the I/P dimmer switch to a low position.
Are the I/P lamps on?
YES - Go to Testing for Intermittent Conditions and Poor Connections
NO - Go to Step 3
3
Disconnect the headlamp switch.
Using a test lamp connected to a known good ground, probe the park lamp switch ON circuit at the headlamp switch.
Does the test lamp illuminate?
YES - Go to Step 5
NO - Go to Step 4
4
Repair a poor connection or an open in the park lamp switch ON circuit.
YES - Did you complete the repair?
NO - Go to Step 10
--
5
Using a test lamp, probe the headlamp switch between the park lamp ON circuit and the I/P dimmer switch control circuit.
Does the test lamp illuminate?
YES - Go to Step 6
NO - Go to Step 7
6
Replace the headlamp switch.
Refer to Headlamp Switch Replacement .
Did you complete the repair?
YES - Go to Step 10
--
7
Inspect the I/P dimmer switch control circuit for a poor connection, or an open.
Is the circuit OK?
YES - Go to Step 9
NO - Go to Step 8
8
Repair a poor connection, short to ground or an open in the I/P dimmer switch control circuit.
Did you complete the repair?
YES - Go to Step 10
--
9
Replace the LH I/P accessory wiring junction block.
Did you complete the repair?
YES - Go to Step 10
--
10
Operate the system in order to verify the repair.
Did you correct the condition?
YES -- Go to Diagnostic System Check - Lighting Systems
NO Go to Step 2

Headlights Circuit Description
The headlights are controlled by the body control module (BCM) via the AHL Relay when the headlamp and panel dimmer switch is the AUTO position. When in the AUTO mode, the BCM receives a signal, (voltage) from the ambient light sensor, based on the voltage of the signal of n the sensor the BCM turns the day time running lamp (DRL) lights OFF and the headlights ON. The headlights can also be turned on by placing the headlamp and panel dimmer switch in the head position.
The relay coil is fed by the headlamp and panel dimmer switch or the BCM and the battery B+ buss bar in the underhood bussed electrical center (UBEC). The BCM supplies current to the relay based on the input from the ambient light sensor via CKT 352.
The relay output feeds the LT HDLP and RT HDLP fuses to supply current to the low and high beam lamps on CKT 1340 and CKT 1240. The ground for both the low and high beam lamps is supplied via CKT 524 and CKT 525 to the dimmer switch. The dimmer switch uses CKT 1850 for a ground to G203.
Some circuits are monitored by the BCM, and upon failure may set a DTC.
Park/Side Marker and Tail Lamps
The park/side marker and tail lamps are split between the following 4 fuses:
?€¢
The FR PRK

?€¢
The LR PRK

?€¢
The RR PRK

?€¢
The TRL PRK

These fuses receive voltage from the park lamp relay. When the headlamp and panel dimmer switch is in the auto position, the body control module (BCM) controls the relay by grounding CKT 1080 based on the input of the ambient light sensor. The park LPS fuse supplies battery positive voltage (B+) to the relay at all times.
When the headlamp and panel dimmer switch is in the PARK position, the relay is by passed through the INT PRK fuse. Current flows from the PARK LPS fuse through the headlamp and panel dimmer switch to the INT PRK fuse in order to feed the following fuses:
?€¢
The FR PRK

?€¢
The LR PRK

?€¢
The RR PRK

?€¢
The TRL PRK

Park Lamps Inoperative

Step

Action

Value(s)

Yes

No

1

1. Turn the ignition OFF.
2. Connect a scan tool.
3. Turn the ignition to the ON position.
4. Using the scan tool, check for any DTCs in the body control module (BCM).

Does the scan tool show any DTCs ?
--
Go to Diagnostic System Check - Body Control System in Body Control System
Go to Step 2

2

1. Turn the headlamp switch to the park position.
2. Connect a test lamp from (back probe) terminal B of the headlamp and panel dimmer switch to ground.

Does the test lamp light?
--
Go to Step 4
Go to Step 3

3

Locate and repair the open in CKT 240 (ORN) between the switch and the mid bussed electrical center (MBEC).

Is the repair complete?
--
System OK
--

4

Connect a test lamp from (back probe) terminal A of the headlamp and panel dimmer switch to ground.

Does the test lamp light?
--
Go to Step 6
Go to Step 5

5

Replace the headlamp and panel dimmer switch. Refer to Headlamp Switch Replacement .

Is the repair complete?
--
System OK
--

6

Connect a test lamp from the INT PRK fuse, located in the left bussed electrical center (LBEC), to ground.

Does the test lamp light?
--
Go to Step 7
Go to Step 8

7

Locate and repair the open in CKT 74 (LT BLU) between the MBEC and the UBEC.

Is the repair complete?
--
System OK
--

8

Locate and repair the open in CKT 74 (LT BLU) between the headlamp and the panel dimmer switch and the LBEC.

Is the repair complete?
--
System OK

Park lamp fuse 20amp located in the under hood fuse box .DRL control module
Daytime Running Lamps (DRL) Control Module
Right of the steering column, behind the IP
Park, Sidemarker, Tail and License Lamps
Voltage is applied continuously to the PARK fuse to the headlamp and the instrument panel (IP) lamp dimmer switch through CKT 1340.
When the headlamp and the (IP) lamp dimmer switch is in the PARK or HEAD position, voltage is applied to CKT 9 thus activating the following lamps:
• The park lamps
• The side marker lamps
• The tail lamps
• The license lamps
The park/turn lamps are the only lamps that do not activate yet receive a current from CKT 9. The park/turn lamps do not activate because the voltage drop across the front side marker lamps is much higher than that across the turn lamp filaments Step
Action
Normal Result(s)
Abnormal Result(s)*

1
Turn the headlamp/instrument panel (IP) lamp dimmer switch to the PARK position.
The following lamps light:
• The license plate lamps
• The taillight lamps
• The front side marker lamps (Domestic)
• The front parking lamps (Domestic)
The headlamp position lamps (Export)
Refer to Park Lamps Inoperative
Park Lamps Inoperative
Step
Action
Value(s)
Yes
No

1
Inspect the PARK LP fuse.
Is the fuse open?
--
YES - Go to Step 2
NO - Go to Step 3

2
Repair a short to ground in CKT 1340.
Is the repair complete?
--
Go to Exterior Lights System Check
--

3
Turn the headlamp/instrument panel (IP) lamp dimmer switch to the PARK position.
Use a test light in order to backprobe the headlamp/IP lamp dimmer switch harness connector between terminal R and ground.
Did the test lamp light?
--
Go to Step 7
Go to Step 4

4
Use a test light in order to backprobe the headlamp/IP lamp dimmer switch harness connector between terminal O and ground.
Did the test lamp light?
--
Go to Step 5
Go to Step 6

5
Replace the headlamp/IP lamp dimmer switch. Refer to Headlamp Switch Replacement .
Is the repair complete?
--
Go to Exterior Lights System Check
--

6
Repair the following conditions in CKT 1340 between the PARK LP fuse and the headlamp and the IP lamp dimmer switch harness connector terminal O:
• A faulty connection
• An open circuit
Is the repair complete?
--
Go to Exterior Lights System Check
--

7
Repair the following conditions in CKT 9 between the headlamp and the IP lamp dimmer switch harness connector terminal R and S204:
• A faulty connection
• An open circuit
Is the repair complete?
--
Go to Exterior Lights System Check

Battery positive voltage (B+) is supplied through the LH underhood fuse block LCM/HDLP circuit breaker via CKT 242 (RED) at all times to the following components:
?€¢
Headlamp switch

?€¢
Lamp control module (LCM)

?€¢
Switch of the RH IP fuse block headlamp relay position J

When the headlamp switch is placed in the ON position, battery positive voltage (B+) is supplied via CKT 10 (YEL) to the coil of the headlamp relay position J. The coil is permanently grounded to G201 via CKT 1450 (BLK). The coil is energized and the contacts close providing battery positive voltage (B+) to the headlamp dimmer switch via CKT 1346 (LT BLU). When the headlamp dimmer switch is in the LOW position, battery positive voltage (B+) is supplied via CKT 12 (TAN) to the following components:
?€¢
Left low beam headlamp

?€¢
Right low beam headlamp The LCM provides battery positive voltage (B+) via CKT 1346 (LT BLU) through the headlamp dimmer switch to the headlamps under the following conditions:
?€¢
The ignition switch is in the RUN position.

?€¢
The ambient light sensor indicates darkness.

The lamp control module (LCM) monitors the ambient light conditions through the ambient light sensor. The ambient light sensor is a variable resistor whose resistance changes as the surrounding ambient light level changes. As the ambient light decreases, the resistance of the ambient light sensor increases. The LCM measures the resistance across the ambient light sensor and determines whether it is day or night.
Headlamps Inoperative - Low Beams (Oldsmobile)
This is a lengthy diagnostic flow chart .

1

Did you perform the headlights system check?
--
Go to Step 2
Go to Headlight System Check

2

1. Disconnect the lamp control module (LCM) connector C1.
2. Connect a DMM from the LCM connector C1 cavity E (RED) to ground.

Is the voltage within the specified range?
10-15V
Go to Step 3 yes
Go to Step 9 no

3

Use a test lamp in order to backprobe the headlamp switch connector from cavity D (RED) to ground.
Does the test lamp light?
--
Go to Step 4
Go to Step 10

4

1. Remove the headlamp relay position J from the RH IP fuse block.
2. Connect a DMM from the headlamp relay position J cavity 30 (RED) to ground.

Is the voltage within the specified range?
10-15V
Go to Step 5
Go to Step 11

5

1. Place the headlamp switch in the HEAD position.
2. Connect a DMM from the headlamp relay position J cavity 85 (YEL) to ground.

Is the voltage within the specified range?
10-15V
Go to Step 6 yes
Go to Step 12 no

6

Connect a DMM from the headlamp relay position J cavity 30 (RED) to cavity 86 (BLK).
Is the voltage within the specified range?
10-15V
Go to Step 7 yes
Go to Step 14 no

7

Connect a fused jumper from the headlamp relay position J cavity 30 (RED) to cavity 87 (LT BLU).
Do the low beam headlamps light?
--
Go to Step 15 yes
Go to Step 8 no

8

1. Leave the fused jumper in place.
2. Use a test lamp in order to backprobe the headlamp dimmer switch connector C202 from cavity C5 (LT BLU) to ground.

Does the test lamp light?
--
Go to Step 17 yes
Go to Step 16 no
Repair the open in CKT 242 (RED) between S201 and the LCM. Refer to Wiring Repairs in Wiring Systems.
Is the repair complete?
--
Go to Headlight System Check
--

10

Repair the open in CKT 242 (RED) between S201 and the headlamp switch. Refer to Wiring Repairs in Wiring Systems.
Is the repair complete?
--
Go to Headlight System Check
--

11

Repair the open in CKT 242 (RED) between S201 and the RH IP fuse block. Refer to Wiring Repairs in Wiring Systems.
Is the repair complete?
--
Go to Headlight System Check
--

12

Inspect for an open in CKT 10 (YEL) between the headlamp switch and the RH IP fuse block. Refer to Testing for Continuity in Wiring Systems.
Is CKT 10 OK?
--
Go to Step 13
Go to Step 19

13

Replace the headlamp switch. Refer to Instrument Cluster Trim Panel Replacement in Instrument Panel, Gauges and Console.
Is the repair complete?
--
Go to Headlight System Check
--

14

Repair the open in CKT 1450 (BLK) between the RH IP fuse block and S308. Refer to Wiring Repairs in Wiring Systems.
Is the repair complete?
--
Go to Headlight System Check
--

15

Replace the headlamp relay position J in the RH IP fuse block.
Is the repair complete?
--
Go to Headlight System Check
--

16

Repair the open in CKT 1346 (LT BLU) between the RH IP fuse block and the headlamp dimmer switch connector C202. Refer to

17

Inspect for an open in the CKT 12 (TAN) wiring between the headlamp dimmer switch connector C202 and S257. Refer to Testing for Continuity in Wiring Systems.
Is CKT 12 OK?
--
Go to Step 18
Go to Step 19

18

Replace the headlamp dimmer switch. Refer to Dimmer Switch Assembly - Disassemble - Off Vehicle and Dimmer Switch Assembly - Assemble - Off Vehicle in Steering and Column-Tilt.
Is the repair complete?
--
Go to Headlight System Check
--

19

Repair the suspect wiring. Refer to Wiring Repairs in Wiring Systems.
Is the repair complete?
--
Go to Headlight System Check

Headlamps Inoperative - Low Beams

Step

Action

Value(s)

Yes

No

DEFINITION: This diagnostic procedure should only be used if the high beam headlamps are operating properly and the low beams are inoperative.

1

Did you perform the Headlights System Check?
--
Go to Step 2
Go to Headlight System Check

2

1. Turn the headlamp and panel dimmer switch to the ON position.
2. Move the headlamp dimmer switch to the LOW position.
3. Backprobe the headlamp dimmer switch connector with a J 35616-200 from cavity A to ground.

Does the test lamp light?
--
Go to Step 3
Go to Step 5

3

1. Remove the daytime running lamp relay.
2. Connect a J 35616-200 at cavity G5 to ground.

Does the test lamp light?
--
Go to Step 4
Go to Step 6

4

1. Re-install the daytime running lamp relay.
2. Backprobe cavity B at the high/low beam headlamp with the headlamp dimmer switch in the LOW position.

Does the test lamp light?
--
Go to Step 7
Go to Step 8

5

Replace the headlamp dimmer switch.

Is the repair complete?
--
Go to Headlight System Check
--

6

Repair the open in CKT 359 (PPL) between the headlamp dimmer switch and the daytime running lamp relay.

Is the repair complete?
--
Go to Headlight System Check
--

7

Replace the high/low beam headlamps.

Is the repair complete?
--
Go to Headlight System Check
--

8

1. Inspect for an open in CKT 12 (TAN) between the daytime running lamp relay and S120, repair as necessary.
2. Replace the daytime running lamp relay if no open was found in CKT 12 (TAN) between the daytime running lamp relay and S120.

Is the repair complete?
--
Go to Headlight System Check
--

Were the headlights out before you replaced the switch or after.Why did you replace dimmer switch. Did you disconnect the battery before repair. Were any other lights out before this repair? Dimmer switch in this car is in with the blinker light assembly.
I think you pinched some wires during your repair, and if so you blew a fuse or two. I would go back and retrace my steps, see that no wires are pinched, or touching metal, and check fuse panel left side dash board and control center under hood left side.
If you didn't disconnect battery before you started, check your fuses first. This would be the first and simplest step. I would like to hear how you made out. GOOD LUCK.

Factory repair manual step by step testing procedure for Interior Backlighting Inoperative. In your course of testing let me know if you need location for anything .

2
Turn ON the parklamps.
Ensure the panel dimmer switch is at maximum illumination.
Do the illumination lamps operate normally?
YES - Go to Testing for Electrical Intermittents in Wiring Systems
NO - Go to Step 3
3
Is only one lamp inoperative?
YES - Go to Step 4
NO - Go to Step 6
4
Test the instrument panel lamp supply voltage circuit of the inoperative lamp for high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
YES - Go to Step 17
NO - Go to Step 5
5
Test the ground circuit of the inoperative lamp for high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
YES - Go to Step 17
NO - Go to Step 11
6
Do the park lamps function properly?
YES - Go to Step 7
NO - Go to Park Lamps Inoperative
7
Inspect the ILLUM fuse.
Is the fuse open?
YES - Go to Step 12
NO - Go to Step 8
8
Ensure the panel dimmer switch is at maximum illumination.
Connect a test lamp between the ILLUM fuse and ground.
Does the test lamp illuminate?
YES - Go to Step 14
NO - Go to Step 9
9
without disconnecting the switch, connect a test lamp between the instrument panel lamps dimmer switch signal circuit at the headlamp and panel dimmer switch and ground.
Does the test lamp illuminate?
YES - Go to Step 13
NO - Go to Step 10
10
Inspect for poor connections at the harness connector of the headlamp and panel dimmer switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
YES - Go to Step 17
NO - Go to Step 16
11
Inspect for poor connections at the harness connector of the inoperative bulb. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
YES - Go to Step 17
NO - Go to Step 15
12
Repair the short to ground in the instrument panel lamp supply voltage circuit. Refer to Wiring Repairs in Wiring Systems.
Replace the fuse.
YES - Did you complete the repair?
NO - Go to Step 17
--
13
Repair the open in the instrument panel lamps dimmer switch signal circuit between the switch and the fuse. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?
Go to Step 17
--
14
Repair the open in the instrument panel lamp supply voltage circuit. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?
Go to Step 17
--
15
Replace the inoperative bulb.
Did you complete the replacement?
Go to Step 17
--
16
Replace the headlamp and panel dimmer switch. Refer to Headlamp Switch Replacement .
Did you complete the replacement?
Go to Step 17
--
17
Operate the system in order to verify the repair.
Did you correct the condition?
System OK
Go to Step 3

it is both replacable and repairable.
1. remove steering wheel
2. take off locking plate with two screwdrivers
3. remove locking plate
4. remove retaing screws and take out turn signal lever
5remove screws from hazzard switch (3)
6.take off panel under the dash to get to wire harness
7.remove harness and switch assembly

use wire or string tied to harness to pull that back thru the steering column

You need to take the vehicle back to whoever repaired it for there's a rod running down from your dimmer switch to the actual dimmer switch mounted above your ankles which should be white and/or green and it has two 5/16" nuts or 8 mm, same thing, and the headlight dimmer switch is slotted to move it up or down the column to make contact. You can do this yourself in loosening the bolts, turning on the headlights, and when they stay on, lock down one of the 8 mm bolts, then check the dimming feature and if it's still not correct, loosen the bolts just enough to move the switch (with the rod coming down from the steering wheel) just enough to "fine-tune" your adjustment.

"00 Buck"

My son came down and figured it out for me. Not sure what all he did but he had to make a few modifications by splicing the wires together after cutting the wires just under the dimmer switch...then a few adjustments were needed to get it to all work right.
Thanks