Electrical Headlights

FrankenStang88

New Member
Feb 2, 2016
21
0
1
Arizona
So i recently purchased a headlight and foglight switch for my 88 because before i had to find a sweet spot when trying to get the headlights to stay on. I got a new one and now they wont even turn on. The only thing that works is my high beams(when you pull back the turn signal lever). I dont know if its as easy as a blown fuse or the connector in the back of the switch is bad.
 
  • Sponsors(?)


jrichker

StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
27,436
2,869
234
74
Dublin GA
lowendmac.com
The Multifunction/turn switch also cause problems with the headlights and foglights.

Multifunction turn signal switch:
Before you think about replacing the multifunction switch with one from the junkyard, here are some things to be aware of...

The problem is more common in GT models because they had fog lights on the same power wiring as the headlights. Ford undersized the wire and that caused problems.

A word of caution about multifunction switches is in order here. The multifunction switch (high/low beam, wiper, turn signals) are different for different years. 87-98 will work in any 87-89 car. The 90-93 switches only work in 90-93 cars. You can't put an early model switch in a late model car, nor can you put a late model switch in an early car.

Supposedly you can move the pins around to make the switches work in model years that are different from the car the switch came out of. I cannot verify that and haven’t tried it.

Other possible problem sources for the turn signal & headlight malfunction are the ignition switch, multifunction switch and the plastic shell that holds the turn signal wiring connector pins.

The following diagram is for 87-89 model cars.

Turn signal switch wiring:
attachment.php?attachmentid=35089&d=1117654157%20.gif
The following diagram is for 90-93model cars.

Turn signal switch wiring:
?temp_hash=b51bc221374cd74935f89f5677f78d9b.jpg





Foglight fix
SEE Mustang GT Fog Light Fix to fix the foglight problem. The stock wiring isn't up to the job and is overheating. The headlight switch & turn/multifunction switch are affected by Ford's wiring problem. Sometimes it overheats so badly that the plastic shells of the wiring connectors start to melt. This will show you how to add a relay to the fog lights to relieve the overload on the headlight wiring.

Be careful not to use bulbs rated at more than 55 watt each with the stock fog light wiring. Using oversize bulbs can result in overheating the wiring harness and electrical fires. Definitely do the fog light fix first.

I did mine differently, but I had to build my own wiring harness for the fog lights. This is more trouble than it is worth for most folks. I left all the wiring on the stock light switches in place and used the fog light wiring to power the relay coil. The other side of the relay coil is connected to ground. I have an inline fuse that picks up power from the battery side of the starter solenoid. It is connected to the relay contact. The other relay contact is connected to the new wiring harness I made for the fog lights.

attachment.php?attachmentid=50532&stc=1&d=1180230049.gif


The advantage of making your own foglight wiring harness is that you can run 100 watt fog light bulbs. The stock wiring harness will not use 100 watt bulbs without overloading and causing a fire.

Unless you are good at electrical wiring, have the skills and tools (crimp tool, soldering gun, heat gun for the heat shrink tubing, etc.) I recommend that you stick with the Corral method.

Technical explanation of why the wiring and switches overheat.
You asked for it...

I= Current
E= Voltage
R= Resistance
W= Watts

Two 55 watt fog lamps =110 watts. Find the current in the circuit
I= W/E
110 watts/14 volts = 7.85 amps for fog lights alone.
Since the lighting circuit supplies headlights, taillights, and parking lights, etc.

56 watts 2 each GE Part # L3156 corner light 28 watts each
90 watts 2 each GE Part # 9004 headlight 45/65 watts each (low beam)
63 watts 2 each GE Part # L194 parking light 31.5 watts each
56 watts 2 each GE Part # L3157 tail light 28 watts each
265 watts Total

Total other exterior lighting current
I=W/E
265 watts/14 volts = 18.92 amps
18.92 amps other exterior lighting current
+ 7.85 amps fog light current
26.77 amps with all exterior lights and fog lights on.

The 12 gauge power feed wire to the exterior lighting switch is rated at 20 amps
26.77
- 20.00
6.77 amps excess current

7.85 amps used by fog lights
-6.77 amps excess current
1.08 amps to run the fog lights left if you stay within the 20 amp limit of the wire.
With 1.08 amp of current, the fog lights probably won’t produce any useable light.

Added resistance required to reduce fog light current to permissible 20 amp limit
R=E/I
14 volts/6.77 amps = 2.06 ohms
Resistor wattage
W=EI
14 volts x 6.77 amps = 94.78 watts
You would need a 2 ohm, 100 watt resistor.

Light bulb ratings from http://www.roadparts.com/catalog/section30.pdf
Radio shack resistor catalog - no matches , and no combinations that could be used to make a 100 watt, 2 Ohm resistor.
See RadioShack.com

Ohm’s law – in case you have any questions about my formulas - Ohm's Law Calculators
 
Thread starter Similar threads Forum Replies Date
R Headlights SN95 4.6L Mustang Tech 0
umangu LED Headlights 1965 - 1973 Classic Mustangs -General/Talk- 7
M For Sale FS: OEM Saleen HID Headlights Interior Exterior Parts 0
R 1969 mustang headlight upgrade wiring kit 1965 - 1973 Classic Mustangs -General/Talk- 0
Rdub6 Paint and Body Headlight Bolts Fox 5.0 Mustang Tech 6
JD08 Time to refresh my headlights 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 3
R 2012 mustang stock headlights 2005 - 2014 S-197 Mustang -General/Talk- 3
zack2001 2005 Mustang 4.0 Raxiom sequential taillights act up when headlights are turned on 2005 - 2009 Specific Tech 1
B Paint and Body '86 Four Eye Headlight Fiberglass Assembly - Repair or Replace? Fox 5.0 Mustang Tech 4
8 Headlight Switch Electrical Question Fox 5.0 Mustang Tech 2
R Lightswitch diagram/function Mustang II 1974 - 1978 Mustang II Talk & Tech 12
F Headlights? - An Other Stuff that's [not] Headlights 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 134
E Custom mod to 2002 gt stock headlights SN95 4.6L Mustang Tech 1
M Headlights On When Car is Off/Parked and Raining - S550 2015+ (S550) Mustang -General/Talk 5
Will L. How do I wire DRL headlights properly 1996 - 2004 SN95 Mustang -General/Talk- 1
T Headlights come on and then tail lights go off Fox 5.0 Mustang Tech 3
S Electrical Brake lights on with headlights Fox 5.0 Mustang Tech 1
9 1995 GT convertible Electrical gremlin 1994 - 1995 Specific Tech 1
S Headlight Upgrade for 2011 Stang 2010 - 2014 Specific Tech 0
shufixer 2000 GT Headlight replacement issues 1996 - 2004 SN95 Mustang -General/Talk- 0
F Anybody have experience changing halogen headlights to HIDs or LEDs? 1996 - 2004 SN95 Mustang -General/Talk- 3
Boricua86 Electrical 1986 GT Headlight Upgrade Fox 5.0 Mustang Tech 11
Red50Fox Aftermarket headlights: Pros and Cons 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 64
EZ123 Halo headlights? 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 8
B For Sale Headlight Covers - $50 Interior Exterior Parts 0
M New to Community - Headlight Bulb - 2000 3.8L V6 Base 1996 - 2004 SN95 Mustang -General/Talk- 0
T Headlight replacement compatibility 1996 - 2004 SN95 Mustang -General/Talk- 1
B Engine Misfire only with headlights on Fox 5.0 Mustang Tech 25
A Electrical Headlight and turn signal problems Fox 5.0 Mustang Tech 3
Colb Raxiom Smoked projector bulb change 1996 - 2004 SN95 Mustang -General/Talk- 0
E water spots and possible scratches on headlights, any recommendations on cleaning headlights? 2015+ (S550) Mustang -General/Talk 0
gearhead77 Paint and Body Headlight cleanup 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 18
billison Making aftermarket headlights last.. 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 0
J Electrical 94 Gt Headlights not working 1994 - 1995 Specific Tech 4
S Headlights - both hi and low beam on at the same time Fox 5.0 Mustang Tech 8
K 1993 GT - Headlight Relay Mod Advice Fox 5.0 Mustang Tech 11
N Question about headlights switch (1979 - 1981) 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 1
T 2002 V6 Headlight Conundrum 1996 - 2004 SN95 Mustang -General/Talk- 0
9 Need Help on what I need - New to the game 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 4
K 1968 Mustang Wiring issues 1965 - 1973 Classic Mustangs -General/Talk- 4
N New Headlights, Low Beams not working, Hi-Beams half working 1996 - 2004 SN95 Mustang -General/Talk- 3
I Electrical help! 03 mustang headlights 1996 - 2004 SN95 Mustang -General/Talk- 2
D Best 1-piece headlight fitment? 1994 - 1995 Specific Tech 1
C headlight switch connector 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 14
T Electrical 88 Headlight issues. Fox 5.0 Mustang Tech 6
FetusLasVegas Electrical 89 GT, Front turn signals not illuminating with headlights Fox 5.0 Mustang Tech 2
a_bartle One piece headlights for '94 to '98 Mustangs.... 1996 - 2004 SN95 Mustang -General/Talk- 0
T bad headlight switch? 1994 - 1995 Specific Tech 1
P For Sale [FS] 65/66 NOS Fenders, Front Apron. Also Knock-off Caps, Headlight Extensions, etc [New Orleans, LA] Interior Exterior Parts 3
K Need help with headlight harness/switch/wiring in 2000 Mustang 1996 - 2004 SN95 Mustang -General/Talk- 2
Similar threads