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1989 Bronco XLT 5.8 gutted beater lol
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Discussion Starter · #1 ·
So every time I pull the headlight switch, fuse #10 blows. I used a multimeter and it seems to be a short to ground. Instead of blowing through all my fuses, I just plugged a 12v light into the fuse socket. If the light is on, there's a short. I've been looking through wiring diagrams for weeks and unplugging literally everything one at a time, no progress obviously. The entire truck is gutted, dash, radio and ac is completely removed, that could help find the short if its in that area. I've already replaced the headlight switch, and no the coil on the old switch didn't melt off and short something out like I've heard they can do...

My real question is, what exactly is everything that's on this circuit? Where are common spots where wires could short to ground?
 

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Yo RileyRay3D,
For now untilI or others can offer known perpetrators.
181797

181798

181799
181800
G701 "...Behind Instrument Panel near RH side of Radio..."
Source: by Ryan M (Fireguy50) at FSB
 

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1989 Bronco XLT 5.8 gutted beater lol
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3 Posts
Discussion Starter · #3 ·
Thanks for the reply! I've unplugged everything on this circuit and it still shorts out. I was hoping it was something common and obvious but this is turning out to be a real pain. I hope ill eventually find it but I cant spend hours every day on it. Gonna be road tripping in this thing in a few months so ill take it to a professional if I don't figure it out by then
 

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Yo RileyRay3D,

Inspect dear window defroster circuit.

Inspect cigar lighter wiring for possible drain.
Our 96's (bought new) wiring was pinched under at ashtray support.
Switch Fires, Part Number SW-2103: "...Over the past two years, this office has experienced fires caused by another potential problem in Ford vehicles. The problem exists within the dimmer portion of the headlight switch in Ford vehicles. The light switch involved is a Model SW-2103. These are the pull out type headlight switches usually located in the lower left corner of the front dash of Ford vehicles. The headlight portion of the switch has two pullout positions, the first for parking lights only, and fully out for headlights and parking lights. The shaft of this pull-out light switch can be turned clockwise and counterclockwise which activates a dimmer switch, lowering and raising the intensity of the lighting in the instrument panels respectively. Fully rotating the shaft counterclockwise past a notch activates the interior lights within the vehicles. The potential problem exists within the dimmer portion of this switch. The dimmer mechanism consists of a metallic resistive coil set inside a ceramic disc positioned over the shaft of the switch. The coil is exposed on its front side away from the passenger compartment. The front side of the coil passes across a contact permitting a current to flow through a certain portion of the coil when the switch is pulled our in its first or second positions. The greater amount of coil through which the current is permitted to pass (clockwise most position) creates the greatest resistance and therefore dims the dash lighting to its lowest intensity. The opposite position provides greatest intensity. Through our investigations, we have found that the coil can fail owing to wear and/or possible material defects or damage. A fractured coil can maneuver itself free of the ceramic disc permitting it to come in contact with the metal bracket which mounts and grounds the switch to the vehicle. When this occurs, a current can flow through a portion of the coil creating high temperatures melting the metal material of the coil and possibly igniting surrounding combustibles. This mechanism has been observed in three separate incidents by this office. Two of these resulted in a fire. The mechanism is precipitated by wear and/or defect in the coil mechanism. If the former is true, we expect there will be an increase in fires caused through this mechanism given an increase in service time. To this date the problem appears to be somewhat limited. However, this particular light switch has been utilized in numerous Ford vehicles. Therefore, a small increase in failure rate owing to age and wear could result in a significant increase in fire losses. The SW-2103 Light Switch Assembly discussed above is reportedly installed in the following Ford vehicles: 1986 -1997 F100, F150, F300; 1990-1994 Explorer; 1987-1994 Ranger; 1987-1990 Bronco II; 1992-1997 Aerostar..." Miesk5 NOTE: No Bronco Listed, but this may be the result of typos or incomplete research by the company.

Inspect Dimmer Switch Connector Behind Dash
 

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1989 Bronco XLT 5.8 gutted beater lol
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3 Posts
Discussion Starter · #5 ·
Ok so I was fiddling around with it today and wiggling the wire harness above the radio area when the light I had plugged into the fuse socket (for testing the ground short) finally went off and now the illumination lights are back on! All the wires coming from the harness aren't touching anything (such as the radio and cigarette lighter wires) So somewhere close to where I was wiggling the harness is the problem clearly. The issue started randomly when I was Driving so it'll probably come back soon, and I don't wanna have to keep replacing fuses. At least I have a clue and ill keep trying to find it, tho ill probably just wait till it shorts out again, and maybe secure any loose wires better for the time being. Thanks for the help!
 
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