Help keep blowing fuse for brake taillights.can't put shifter in drive.
10-27-2015, 01:20 PM
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Help keep blowing fuse for brake taillights.can't put shifter in drive.
I have 2001 grand Cherokee keeps blowing brake lights fuse.disconnected both rear taillights and brake switch on brake pedal still keeps blowing the fuse and can't move shifter out of park.any suggestions greatly appreciated.
10-27-2015, 02:04 PM
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Thanks for the reply.doing a little bit of research I don't think its the shifter bezel.it won't go into drive because it keeps blowing brake light fuse.need some help ad why it keeps blowing fuse.even when I disconnected both twilights and brake switch???????
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10-27-2015, 03:37 PM
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Appreciate all your help.this all started when the left rear brake light socket melted the plastic on the tail light circuit board. Disconnected both taillights plus brake switch. Still blows fuse.any suggestions where to start looking for a pinched wire??
10-27-2015, 04:35 PM
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10-27-2015, 07:48 PM
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SeriousOffroad gave some good tips to start with. Inspection may reveal things that are worthy of closer investigation and starting at the point of the first visible discovery is probably best. Just don't lose your view of the forest because you're looking too closely at the tree.
Normally, understanding the original failure-mode helps with the debug job. The damage is already done now, so finding that is the only thing that matters. Unfortunately, because this began with a meltdown, it is more likely to be a melted wire (or several wires). Important - Do you have a multi-meter or a test light? They are invaluable tools at times like this.
Please bear with my line of reasoning for a moment because without schematics I'm just brainstorming. Hopefully to help with visualization. I believe that the circuit from the fuse to the lamp sockets is +12V, that the brake light switch is normally open and it completes the light circuit (switch closes) when you step on the pedal thus lighting the brake lights (normally). When the switch closes it energizes other "downstream" components, such as a shift lock.
I think you're saying that the fuse blows instantly upon installation without touching the brake pedal. (This is probably why you cannot shift from Park - because the circuit after the brake light switch includes a path through the shift lock solenoid. This can be defeated with a jumper if necessary - bypassing shorted circuit wires and light switch.)
You most likely have a short circuit to Ground. Measuring the resistance to Ground from several test-point locations will help you (approximately) determine the location of the short - at least in the zone at which end of the harness it's at - where you find the lowest resistance value. Once you're "in the zone" you can manipulate wires/harness until the continuity of the short is lost - that's when you'll find the fault.
Normally, understanding the original failure-mode helps with the debug job. The damage is already done now, so finding that is the only thing that matters. Unfortunately, because this began with a meltdown, it is more likely to be a melted wire (or several wires). Important - Do you have a multi-meter or a test light? They are invaluable tools at times like this.
Please bear with my line of reasoning for a moment because without schematics I'm just brainstorming. Hopefully to help with visualization. I believe that the circuit from the fuse to the lamp sockets is +12V, that the brake light switch is normally open and it completes the light circuit (switch closes) when you step on the pedal thus lighting the brake lights (normally). When the switch closes it energizes other "downstream" components, such as a shift lock.
I think you're saying that the fuse blows instantly upon installation without touching the brake pedal. (This is probably why you cannot shift from Park - because the circuit after the brake light switch includes a path through the shift lock solenoid. This can be defeated with a jumper if necessary - bypassing shorted circuit wires and light switch.)
You most likely have a short circuit to Ground. Measuring the resistance to Ground from several test-point locations will help you (approximately) determine the location of the short - at least in the zone at which end of the harness it's at - where you find the lowest resistance value. Once you're "in the zone" you can manipulate wires/harness until the continuity of the short is lost - that's when you'll find the fault.
10-27-2015, 08:43 PM
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SeriousOffroad gave some good tips to start with. Inspection may reveal things that are worthy of closer investigation and starting at the point of the first visible discovery is probably best. Just don't lose your view of the forest because you're looking too closely at the tree.
Thanks for your help.I disconnected t
Normally, understanding the original failure-mode helps with the debug job. The damage is already done now, so finding that is the only thing that matters. Unfortunately, because this began with a meltdown, it is more likely to be a melted wire (or several wires). Important - Do you have a multi-meter or a test light? They are invaluable tools at times like this.
Please bear with my line of reasoning for a moment because without schematics I'm just brainstorming. Hopefully to help with visualization. I believe that the circuit from the fuse to the lamp sockets is +12V, that the brake light switch is normally open and it completes the light circuit (switch closes) when you step on the pedal thus lighting the brake lights (normally). When the switch closes it energizes other "downstream" components, such as a shift lock.
I think you're saying that the fuse blows instantly upon installation without touching the brake pedal. (This is probably why you cannot shift from Park - because the circuit after the brake light switch includes a path through the shift lock solenoid. This can be defeated with a jumper if necessary - bypassing shorted circuit wires and light switch.)
You most likely have a short circuit to Ground. Measuring the resistance to Ground from several test-point locations will help you (approximately) determine the location of the short - at least in the zone at which end of the harness it's at - where you find the lowest resistance value. Once you're "in the zone" you can manipulate wires/harness until the continuity of the short is lost - that's when you'll find the fault.
Thanks for your help.I disconnected t
Normally, understanding the original failure-mode helps with the debug job. The damage is already done now, so finding that is the only thing that matters. Unfortunately, because this began with a meltdown, it is more likely to be a melted wire (or several wires). Important - Do you have a multi-meter or a test light? They are invaluable tools at times like this.
Please bear with my line of reasoning for a moment because without schematics I'm just brainstorming. Hopefully to help with visualization. I believe that the circuit from the fuse to the lamp sockets is +12V, that the brake light switch is normally open and it completes the light circuit (switch closes) when you step on the pedal thus lighting the brake lights (normally). When the switch closes it energizes other "downstream" components, such as a shift lock.
I think you're saying that the fuse blows instantly upon installation without touching the brake pedal. (This is probably why you cannot shift from Park - because the circuit after the brake light switch includes a path through the shift lock solenoid. This can be defeated with a jumper if necessary - bypassing shorted circuit wires and light switch.)
You most likely have a short circuit to Ground. Measuring the resistance to Ground from several test-point locations will help you (approximately) determine the location of the short - at least in the zone at which end of the harness it's at - where you find the lowest resistance value. Once you're "in the zone" you can manipulate wires/harness until the continuity of the short is lost - that's when you'll find the fault.
Thank you for your time and help.
10-28-2015, 01:24 AM
#15
Old fart with a wrench
I'm going to jump into this one for a minute. If it's blowing the fuse with the brake switch disconnected, the short has to be in the harness BEFORE the brake switch. This system is hot at all times, so look for something that is likewise hot all the time. Something that is also controlled by that fuse. It's going to take a detailed circuit diagram to find it. The ones I have are a joke! I can't even find the brake switch on mine!