Have short in turn signal only - all lamps work - pops 20 amp fuse after a day or so - problem in turn switch I think. .. Jim

Our professional automotive electronics technician Jeff, provides the answer to a dead short.

Jeff Armer Jan 01, 2024

STOP/ TRN fuse #12 20amp, location - in the instrument panel fuse box. Is this the one? Fuse blows because you have a short circuit on the wiring that fuse protects. Do you know what that is?

Turn Signal Lamps
The STOP/TURN fuse in the instrument panel (I/P) fuse block supplies battery positive voltage to the body control module (BCM) for the turn signal lamps. When the turn switch is placed in the left or right position, ground is applied to the BCM on the left or right turn signal switch signal circuit. The BCM then applies voltage to the appropriate front and rear supply voltage circuits.

Grounds for the various lamps are as follows:

• G100 supplies the right front lamps

• G101 supplies the left front lamps

• G400 supplies the right rear lamps

• G401 supplies the left rear lamps

https://www.youtube.com/watch?v=oKCLzf4va7M&t=807s

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blowing fuse 4 ,F4, 20 amps? (not trailer fuse,marker)
it feeds the brown wire out of head/park switch
13 park lamps on BROWN

well the park feed is shorted clear as day.
only where it shorted matters
park lamps can be 12 lamps.
2 front, 2 read, side lamps
license plate lamp, rear
the seam park feed goes to the cab too.
seems dome is shorted
and lamps sure can short out and the wires
this old easy.
the online manual sticks no dome ckt shown
old trucks then had no digital manual
so all we see today are lamp weak and grossly incomplete scans.
buy a used real F150 manual off ebay OEM real.

The problem may not be the switch unless there is a ground wire running thru it. Most likely, the switch turns on a circuit that has a dead short ( power straight to ground).
Has the car been hit causing a pinched wire? Any recent changes to the car?
I would connect a lamp in instead of the fuse where the fuse goes (to energize the circuit while searching for the short), turn the signal switch on and the lamp should turn on bright. Trace the wiring harness involved and disconnect the harness if possible, at a connector jack, starting near the signal lamp involved. When the dead short is disconnected or removed, the test lamp connected to the fuse holder should dim or shut off.

Good lord there are fuses everywhere in that truck if I remember right, you'd have been better off asking about the problem I think.. try here
http://www.jeep4x4center.com/knowledge-base/index.htm#service
find your truck, pull up the PDF then on your keyboard hit the find box (F3?) punch in "fuse" and run down the list...

For the basic panel
Cavity/Fuse Diagram (1996 Grand Cherokee, passenger side kick plate to find, Owner's Manual pgs 205-206): CAVITY FUSE DESCRIPTION 1 10 amp (RED) Radio 2 15 amp (Lt Blue) Cigarette Lighter 3 10 amp (RED) Rear Washer Switch, Body Controller 4 10 amp (RED) Airbag 5 10 amp (RED) Lamp Out Module, Overdrive Switch, OBD II 6 15 amp (Lt Blue) Vehicle Information Center/Graphic Display Module Park & Side Lamps, Overhead Console Lighted Visor, Automatic Dimming Mirror 7 20 amp (Yellow) Body Amp, Cluster, Body Controller 8 20 amp (Yellow) Rear Wiper Motor, Flipper Glass Solenoid, Cargo Lamp, Trailer Tow 9 15 amp (Lt Blue) Brake Switch 10 10 amp (RED) Rear Window Defroster 11 10 amp (RED) ABS Module 12 10 amp (RED) Heater-Ventilation-A/C Control & Recirculation Motor 13 15 amp (Lt Blue) Hazard Switch, Turn Signal Switch 14 15 amp (Lt Blue) Spare 15 15 amp (Lt Blue) Spare 16 10 amp (RED) Right & Left Courtesy Lamp, Glove Box Lamp, Halo Lamp Cargo Lamp, Underhood Lamp, Dome/Read Lamp Right & Left Visor, Automatic Dimming Mirror 17 15 amp (Lt Blue) Radio Illumination, Tail Lamp, Graphic Display Module, Park & Side Lamps, Headlamp Switch, Body Controller 18 20 amp (Yellow) Spare 19 15 amp (Lt Blue) Passing Light 20 15 amp (Lt Blue) Radio, Heater-Ventilation-A/C, Vehicle Information Center 21 15 amp (Lt Blue) Power Outlet 22 10 amp (Blue) Airbag Module Turn signals are in the flasher and it is located on the driver side below the dash (where the buzzer is located). It is a cylinder type relay. You will find two, one for the hazzard lights and the other for the signals.

Stop lamp circuit discription

Stop Lamps
The STOP LP 25-amp fuse in the underhood fuse block supplies battery positive voltage to the normally open stop lamp switch. When the driver presses the brake pedal, the switch contacts close and battery positive voltage is supplied to both the STOP 15-amp fuse and the center high mounted stop lamp (CHMSL) 10-amp fuse in the instrument panel (I/P) fuse block, and to the turn signal/hazard module. The turn signal/hazard module then supplies voltage to both of the trailer rear turn/stop lamp supply voltage circuits. The voltage from the CHMSL 10-amp fuse is to the CHMSL and the trailer jumper harness. The voltage from the STOP 15-amp fuse is to the stop lamps, throttle actuator control (TAC) module, and the cruise control.

I think The turn signal/hazard module has something to do with the lights flashing .From looking at a wiring diagram B+ voltage from the STOP LP fuse 25amp in the under hood fuse box supply's the brake light switch , from there it feeds B+ to VEH STOP fuse 15amp and VEH CHMSL fuse 10amp an to stop lamp switch signal to the turn signal flasher module which is suppose to control the trailer stop lights . Do you have a connection for a trailer hook up ?
Remove both LT an RT TRLR fuse's both 10 amp from the I/P fuse block an see if the problem goes away .

Do you tow a trailer ? Check the trailer connector for corrosion !

Cavity Fuse Description
1) 15 Amp Blue Horn Relay, Power Sunroof
Relay, Power Window Relay
2) 10 Amp Red Rear Fog Lights (Export Only)
3) 20 Amp Yellow Cigar Lighter
4) 10 Amp Red Headlight Low Beam Right
5) 10 Amp Red Headlight Low Beam Left
6) 20 Amp Yellow Body Control Module/Power Door Locks
7 )10 Amp Red Left Park Light/Left Tail Lamp/License Plate Lamp
8) Spare
9) 10 Amp Red Right Park Light/RightTail Lamp/License Plate Lamp/Cluster
10) Spare Cavity Fuse Description
11) 15 Amp Blue Flasher
12) 15 Amp Blue Stop Lights
13) 10 Amp Red Body Control Module/CMTC/Cluster/Pass. Airbag On,Off Indicator, Auto Daylight
Mirror/Light Bar Switch (Renegade Only)
14) 10 Amp Red PDC Fuel Pump/AC Clutch,
Starter Relay/Engine
Controller/Transmission
Controller (Diesel Only)
15) Spare
16) 20 Amp Yellow Power Outlet (Rear)
17) 15 Amp Blue Rear Wiper
18) 20 Amp Yellow Radio Choke & Relay
Cavity Fuse Description
19 20 Amp Yellow
Frt Fog Lights/Trailer Tow
Stop and Turn Lights
20 Spare
21 10 Amp Red Radio
22 20 Amp Yellow
Power Sunroof Relay/
Antenna Module (Export
Only)
23 Spare
24 10 Amp Red PDC Blower Motor
25 10 Amp Red Heated Seat Switches/HVAC
Control Head/Trailer Tow
Battery Charge
26 10 Amp Red Headlight High Beam Right
27 10 Amp Red Headlight High Beam Left
28 Spare
29 10 Amp Red Heated Mirrors/Rear Window
Defroster Indicator
Cavity Fuse Description
30 15 Amp Blue Heated Seat Module
31 Spare
32 10 Amp Red Wiper Switch/Front and
Rear Wipers
33 10 Amp Red SKIM Module/Data Link
Connector
34 15 Amp Blue Body Control Module/
Cluster/Interior Lights,
Hands Free Module/Radio/
CMTC/ITM Module & Siren
(Export Only)
35 Spare
36 10 Amp Red Airbag Control Module/
Occupation Classification
Module (Right Front Seat)
37 10 Amp Red Airbag Control Module
38 10 Amp Red ABS Controller/Shifter Assembly
39 10 Amp Red Hazard Flasher (Turn
Signals)/Backup Lamp
Switch (Manual Transmission
Only)/Transmission Range
Switch (Automatic Transmis

The Park Lamps and Instrument Panel illumination lamps are controlled by the lighting control module. The problem could be either the headlamp switch or the Lighting control module. Most likely, the head lamp switch.
The most likely cause of the brake lamps not working would be a failed Brake Pedal Position (BPP) switch. It could also be caused by the multifunction switch. To find out if it is the BPP, check for power at the BPP switch. One terminal has a Light Green and Red (LG/R) wire and the other has a Plain Light Green (LT GN) wire. The LG/R wire should be hot at all times. The LT GN wire should be hot only when the pedal is pressed down.

If there is no power at all, there is probably a blown fuse at fuse #10 (20 Amp) in the Central Junction Box (CJB) located uder the left side of the dash. If this fuse is blown, you have a short circuit between the CJB and the BPP switch.

If there is power only on the LG/R wire even with the pedal pressed, then replace the BPP switch.

If there is power on both sides of the BPP then check fuses #20 (7.5 Amp) and #22 (20 Amp) also locatedin the CJB.

If fuse #20 is blown, you have a short between the BPP and the Lighting Control Module. If fuse #22 is blown, you could have a short anywhere from the BPP through the Multifunction Switch all the way back to the brake lamps themselves.

The Brake lamps, Turn Signals, and Park Lamps all share the same ground, so if the Turn Signals are working, it is not likely a ground problem.

Please also review this article: Where's The Fuse?

The turn signal switch is most likely the problem,but change the flasher for the turn signals first,some times this is all that it is.

check the wiring under the carpet and to turn off the day time running lights just pull the drl fuse

I worked for a GM dealership,The problem maybe in the turn signal switch. The brake lamp circuit is wired into it to turn off cruise control.The third brake lamp is a circuit by itself.