• Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech

Electrical Instrument Panel Light Dimmer Switch

  • Thread starter Thread starter alchemist
  • Start date Start date Jul 14, 2019
A

alchemist

New Member
Jul 14, 2019
19
0
1
north carolina
Jul 14, 2019
#1
  • Jul 14, 2019
  • #1
All of a sudden, the instrument panel lights went out last night on my 1991 LX Hatchback. Fuse is fine, and the overhead light still works. I've seen carbon pitting on some of the all in one light switches (and have fixed them), so i removed this one. It has two steel coil style resistor wires wrapped around a plastic shaft. There is one on the top and bottom of a gear drive wheel, and there are two 'points' one on top and one on the bottom, each of which contact the resistors.

I proceeded to use a small cleaning wheel (Dremel) to clean up both the coil wires (weren't all that bad). The points i cleaned up with a small ignition file, and there were also two buttons, again one on top and the other on the bottom, that were at the 'end' of the travel where the overhead/dome light engaged. I cleaned up each button (one was copper colored the other more silver color) as well. Put some D5 Deoxit on the whole thing.

Now, I actually get dash/instrument panel lights full, but in a very very small area of travel, right next to where the overhead light engages. It's easy to get both overhead dome light AND the instrument panel lights on at same time, but getting just the instrument panel lights on without the dome light is tricky. You have to nudge the dial to the left ever so slightly away from the full right setting. But go a little too far and the instrument panel lights go out altogether. The 'fade out' no longer works.

Something is still wrong, obviously. Would anyone have any advice? There appears to be a small resistor inside the unit that you basically can't get to without tearing the thing apart (but i'm thinking about it!). Betting it is bad.

Has anyone rebuilt one of these fully?

Thanks,
Robert Tilton
 

jrichker

StangNet's favorite TOOL
In Remembrance. Thank you for your contributions
Mar 10, 2000
27,512
2,811
234
Dublin GA
Jul 15, 2019
#2
  • Jul 15, 2019
  • #2
The following are diagrams courtesy of Tmoss & Stang&2birds


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring; http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.


TFI module wiring for 94-95 Mustang GT
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-95-IgnitionControlModule.gif

Complete computer, actuator & sensor wiring diagram for 94-95 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/94-95_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 88-90 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

5.0 wiring diagram for Fuel Injectors, Sensors, and Actuators
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

O2 sensor wiring harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangO2Harness.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pin out
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

Mustang 5.0 Lights and Radio schematic, by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxLights-Radio_diag.gif

87-92 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92%20PowerWindowWiring.gif

93 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang93PowerWindows.gif

T5 Cutaway showing T5 internal parts
http://www.veryuseful.com/mustang/tech/engine/images/5_Speed_Cutaway_Illustrated.jpg

Visual comparison of the Ford Fuel Injectors, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/Ford_Injector_Guide.jpg

Convertible top motor wiring http://www.veryuseful.com/mustang/tech/engine/images/mustang88VertTopMotorCkt.gif

Engine mounted fuel injector harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangEngineHarness.gif

Location of the TPS, IAB, and the 10-pin connectors on a 5.0, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/TPS_IAB_Pic.jpg

Starter circuit
http://forums.stangnet.com/attachment.php?attachmentid=21328&d=1080916057

Alternator diagram for 94-95 Mustangs.
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-
 

Saleen0679

10 Year Member
Apr 14, 2005
876
24
49
Yakima, WA
Jul 15, 2019
#3
  • Jul 15, 2019
  • #3
The same thing happened to mine years ago. Seems to be a common problem. After taking a meter to my switch I assumed the rheostat coil was bad somewhere under that green adhesive. That green adhesive crumbled and left a powdery mess so I tossed mine and got a new one. Sometime in the 90s Ford redesigned the switch. The newer design uses a contact pad and wiper that slides across the pad. That 'resistor' you see is probably the thermal fuse.

 
Reactions: jrichker and DSB88GT

jrichker

StangNet's favorite TOOL
In Remembrance. Thank you for your contributions
Mar 10, 2000
27,512
2,811
234
Dublin GA
Jul 15, 2019
#4
  • Jul 15, 2019
  • #4
Saleen0679 said:
The same thing happened to mine years ago. Seems to be a common problem. After taking a meter to my switch I assumed the rheostat coil was bad somewhere under that green adhesive. That green adhesive crumbled and left a powdery mess so I tossed mine and got a new one. Sometime in the 90s Ford redesigned the switch. The newer design uses a contact pad and wiper that slides across the pad. That 'resistor' you see is probably the thermal fuse.

Click to expand...
Which dimmer is the early model and which dimmer is the later model?
 

Saleen0679

10 Year Member
Apr 14, 2005
876
24
49
Yakima, WA
Jul 15, 2019
#5
  • Jul 15, 2019
  • #5
The old style is on the right. It is aluminum and has the coil rheostat. The newer style on the left is all plastic, shorter, and uses contact pads and a wiper as seen through the top.
 
You must log in or register to reply here.

Similar threads

D
Double check my electrical diagnosis of light issues on 65 Coupe
  • Duke City Novice
  • Jan 21, 2024
  • 1965 - 1973 Classic Mustangs -General/Talk-
Replies
1
Views
804
1965 - 1973 Classic Mustangs -General/Talk- Feb 4, 2024
AeroCoupe
W
Electrical Rocker switch on done/map light replacement?? 93 hatch
  • white_stang
  • Aug 11, 2023
  • Fox 5.0 Mustang Tech
Replies
3
Views
815
Fox 5.0 Mustang Tech Aug 12, 2023
85GTStangGuy
T5 with no neutral gear switch on top of case
  • Creomod
  • Feb 6, 2024
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Replies
13
Views
4K
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- Feb 7, 2024
Noobz347
E
Finished my Fox Hydroboost Install - Tips
  • Engineer Duane
  • Apr 9, 2025
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Replies
4
Views
1K
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- May 5, 2025
Engineer Duane
E
Electrical Dimmer Switch
  • Wayne Waldrep
  • Dec 4, 2021
  • Fox 5.0 Mustang Tech
Replies
5
Views
1K
Fox 5.0 Mustang Tech Dec 4, 2021
Wayne Waldrep
Share:
Bluesky Email Share Link
  • Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech
Menu
Log in

Register

  • Forums
  • What's new
  • Media
  • Resources
  • Contact
  • Sponsor
X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?

X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?