Blowing #4 Fuse/ No Tail lights, Cluster, Parking Lights, License Plate light

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mario03srt

mario03srt

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All,

My 1973 Dart has a problem with blowing the #4 fuse. The car is basically a garage queen and has a very good wiring harness with all lighting previously in the car working. During a rare 300 mile round trip I discovered that I had no lights in the dash cluster or rear tails. Upon return I found a blown #4 fuse. Per the Serv Manual this is the fuse for these lights. Swapped in a new fuse and it immedaitely blew w/o any switching on of the lights. I have not been able so far to find the issue.

I inspected the taillights and cleaned and greased everything and no go. I unhooked the rear harness from the main connector and no go. I dropped the fuse box and inspceted it with no visual defects. I removed the working dimmer switch and found this. The switch was still working as I had tried the dimmer before disassembly. I'm going to unplug the parking lights and slap in another fuse to see if they/it is shorted and causing the fuse to blow.

From here I'm not sure where to go. For sure the dimmer and plastic body needs replacement, I suppose that the one cooked lead could be marginal and need insp and maybe replacement too, I see where this is not unusual for these to corrode and fail or have a huge current draw for some reason.

Who has had this issue and what was the cause of # 4 fuse cooking off? Where should I go from here?

Thanks,
Marion

Dimmer 1.JPG


Dimmer 2.JPG
 
Obviously wiring may be the issue but I once had a bulb filament hanging and touching the socket which popped a fuse. So you might want to check your bulbs.
 
do your front signals work? IIRC the tail lights run through the steering column and turn signal switch. Wondering if your signal switch is bad
 
Don't use fuses to determine if a circuit is good. Use the "ohms" setting on a cheap, digital volt meter. Most have a beeper setting when the leads are touched together. Clip one lead to the fuse socket side that goes to the lights, and the other lead to a good ground. Keep unplugging until it stops beeping to help you find where the problem is.
 
j_anderson said:
do your front signals work? IIRC the tail lights run through the steering column and turn signal switch. Wondering if your signal switch is bad
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The turn signals work fine. All of the rear lights are in a harness which come up the driver side and have a connector behind the driver kick panel. Plugged in or not does not affect the #4 fuse blowing.
 
MV8 said:
Don't use fuses to determine if a circuit is good. Use the "ohms" setting on a cheap, digital volt meter. Most have a beeper setting when the leads are touched together. Clip one lead to the fuse socket side that goes to the lights, and the other lead to a good ground. Keep unplugging until it stops beeping to help you find where the problem is.
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Ok I’ll do that.
 
MV8 said:
Don't use fuses to determine if a circuit is good. Use the "ohms" setting on a cheap, digital volt meter. Most have a beeper setting when the leads are touched together. Clip one lead to the fuse socket side that goes to the lights, and the other lead to a good ground. Keep unplugging until it stops beeping to help you find where the problem is.
Click to expand...
Actually this does not always / often work very well, because there is often something else on the circuit that you forgot about, some other accessory, or something the owner or previous owner "hacked" like a stereo and is now shorted. A bettery way is to "rig" a tail/ stop socket (1157) you want a bulb with some current draw, and in this case put alligater jumpers up into the fuse clips and to the stop light bulb. A heavy draw/ short will light the bulb. You can go around shaking/ testing/ disconnecting stuff to test.

For really bad shorts you can do the same thing with a stop light bulb or a headlamp which still works---put the lamp in series with the battery ground.

OP did you look it up--- what all does that fuse supply? I'll assure you it does NOT supply the dimmer because the headlamps get direct power from the ammeter circuit. the light switch has TWO power sources.

One HUGE flag, for me, is that fuse no4 also operates the LIGHTER

Could also be a short in the cluster lighting dimmer circuit, HOW THAT works. Fuse 4 feeds power to B2 on the light switch, which powers tail/ park/ and the dimmer control for the cluster lamps. After power goes through the dash dimmer control, it LEAVES the HL switch on TAN and goes down TO the INST fuse, normally on the end of the panel.Through that fuse and out to all dimmer controlled dash lighting on ORANGE lighting. So if the INST fuse is too large, it may not blow, or the short may be in the dimmer control or that TAN wire

fuses.jpg
 
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I just provided general information on how to test a circuit that is blowing fuses. I don't think the tail bulb is a better way but they both work. The tail lamp bulb is the same test and finds the same "hacks" as the meter, but you have to check/see it with each disconnect versus hearing it and requires a "heavier draw" than a meter beeper.

You can also use door buzzers or anything that runs on 12vdc that can handle continuous operation while testing (not a car horn) and provide an audio indication it is working.
 
67Dart273 said:
Actually this does not always / often work very well, because there is often something else on the circuit that you forgot about, some other accessory, or something the owner or previous owner "hacked" like a stereo and is now shorted. A bettery way is to "rig" a tail/ stop socket (1157) you want a bulb with some current draw, and in this case put alligater jumpers up into the fuse clips and to the stop light bulb. A heavy draw/ short will light the bulb. You can go around shaking/ testing/ disconnecting stuff to test.

For really bad shorts you can do the same thing with a stop light bulb or a headlamp which still works---put the lamp in series with the battery ground.

OP did you look it up--- what all does that fuse supply? I'll assure you it does NOT supply the dimmer because the headlamps get direct power from the ammeter circuit. the light switch has TWO power sources.

One HUGE flag, for me, is that fuse no4 also operates the LIGHTER

Could also be a short in the cluster lighting dimmer circuit, HOW THAT works. Fuse 4 feeds power to B2 on the light switch, which powers tail/ park/ and the dimmer control for the cluster lamps. After power goes through the dash dimmer control, it LEAVES the HL switch on TAN and goes down TO the INST fuse, normally on the end of the panel.Through that fuse and out to all dimmer controlled dash lighting on ORANGE lighting. So if the INST fuse is too large, it may not blow, or the short may be in the dimmer control or that TAN wire

View attachment 1716277934
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Hi,

Thanks for the detailed reply. Yes I have a manual and am aware of the affected lighting components. I have seen the process that you are referring to onYouTube recently using a headlamp. I'll dig into the cig lighter. I've never used it in 8 years. I have new meter on the way with a working beeper. To use you setup I'll need a 1157 bulb and a wired socket? I'm not clear on the connections from the bulb assy to the either/both 2 fuse clips (l and r) and the bulb. Should there be a lead going to ground?

I did a deep dive into the front marker harness both left and right side and did not see any thing of note.

The dimmer does give me concern as to why its cooked, perhaps it was warer soaked back in the day and shorted? I have read that others have had this issue.The only other cooked wire I found on this car was the choke 12v source wire. The firewall distribution block was good and I cleaned and greased it up years ago now.

Is there anything that folks "usually" experience with this fuse issue? A common fail point?

Today I'll peel back some sheath on the harness from the fuse box as far as I can to spot a wire issue etc thats wonky.
 
MV8 said:
I just provided general information on how to test a circuit that is blowing fuses. I don't think the tail bulb is a better way but they both work. The tail lamp bulb is the same test and finds the same "hacks" as the meter, but you have to check/see it with each disconnect versus hearing it and requires a "heavier draw" than a meter beeper.

You can also use door buzzers or anything that runs on 12vdc that can handle continuous operation while testing (not a car horn) and provide an audio indication it is working.
Click to expand...
Actually a buzzer is also a good method. The thing is, an ohmeter can be dangerous to itself, as older ones were not protected from voltage. And, they are sometimes way too sensitive, as it doesn't take much of a load to give an indication. And of course most of them are not audible. My Flukes have an audible alert on low ohms, but I can not hear most of them, certainly not from several feet away.
 
"The harness is good".

How, exactly do you know this?

In my car, it was the brake light shorted through at the bulkhead connector.
 
with your ohmmeter on it's beep function hook it between the #4 fuse blade and a good nearby ground. If you get tone you have a short to ground. You can leave it hooked up while your "searching" and when the tone goes away you are getting close!
 
All,

I'm happy to say that the problem has been resolved! Thanks for all of the input! Turns out that a ground that I had on the firewall for my fuel injection was causing the short. Removed it and voila! Addition by Subtraction! Now I have 100% functional lighting.

Thanks,
FABO!
 
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