Tonight we were cruising down the highway at 60 MPH in our 71 Dart, engine shut down and before I could coast to a stop we had smoke coming from under dash. Got hauled home and discovered main power wire from starter relay to ammeter connection fried at fire wall. Ran wire through bulkhead connectors to replace burnt terminals and thought I had problem solved, no such luck. Still have dead short some where that caused bulkhead terminals to melt. Can ammeter cause this? Wiring diagram indicates power goes to fuse panel, horn relay, headlight switch and ignition switch connector after ammeter. Any idea what could have shorted out going down the road?
Under dash short
- Thread starter craigb
- Start date
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Lots of suspects. I could type examples of what other owners have found all day. Metal straps chaffed through wire looms, rain in the fuse box, and more.
The amp gauges can cause resistance and open circuit but odds that it created a dead short are slim.
The amp gauges can cause resistance and open circuit but odds that it created a dead short are slim.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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"connection fried at fire wall".
I think you answered your own question.This is typical. This particular connection can and often does develop a high resistance to the throughput. That makes heat, smoke,and fire.
Disconnect the battery,Isolate the circuit, Ohm it out.
Since the engine quit, that main powerfeed was interupted.There is,between the firewall and the ignition switch, in the harness, a welded splice. Power branches off from here in at least 4 different directions.Power branches off to 1)the IgSw, 2)the headlamp sw,3) the fusebox,and 4)the horn relay, there may be more.None of these are fused.EDIT; but then you knew that(doh)
Question is; why didnt the fusible link do its job?You do have an F-link, right?
The ammeter is mounted in plastic and is a dead short across the terminals. It is built that way.Inside the ammeter is a short bar across the studs. A very fine insulated wire is wrapped around this bar which, inductively, powers up the needle.
However,that device is mounted very near to the metal dash superstructure. Its difficult, but not impossible, for me to imagine a stud to somehow short to chassis ground there. Poking your head in there, should find it obvious. Those studs are a convenient place (for the factory at least) to tap power off, for other things;such as a convertible top sw(circuit-breakered), or a clock(unfused).
I usually take the seat out. Its waaay more comfortable that way.
I used to carry a long jumperwire, in the gbox.Long enough to jump from the battery to the ballast resistor.And a mini toolkit in the trunk, with something to short the start relay. After that connection left me stranded the first time, I used those items to get me home. Then I cut that wire out and replaced it with one piece, from end to end, and with a new F-link. No more problems.
I think you answered your own question.This is typical. This particular connection can and often does develop a high resistance to the throughput. That makes heat, smoke,and fire.
Disconnect the battery,Isolate the circuit, Ohm it out.
Since the engine quit, that main powerfeed was interupted.There is,between the firewall and the ignition switch, in the harness, a welded splice. Power branches off from here in at least 4 different directions.Power branches off to 1)the IgSw, 2)the headlamp sw,3) the fusebox,and 4)the horn relay, there may be more.None of these are fused.EDIT; but then you knew that(doh)
Question is; why didnt the fusible link do its job?You do have an F-link, right?
The ammeter is mounted in plastic and is a dead short across the terminals. It is built that way.Inside the ammeter is a short bar across the studs. A very fine insulated wire is wrapped around this bar which, inductively, powers up the needle.
However,that device is mounted very near to the metal dash superstructure. Its difficult, but not impossible, for me to imagine a stud to somehow short to chassis ground there. Poking your head in there, should find it obvious. Those studs are a convenient place (for the factory at least) to tap power off, for other things;such as a convertible top sw(circuit-breakered), or a clock(unfused).
I usually take the seat out. Its waaay more comfortable that way.
I used to carry a long jumperwire, in the gbox.Long enough to jump from the battery to the ballast resistor.And a mini toolkit in the trunk, with something to short the start relay. After that connection left me stranded the first time, I used those items to get me home. Then I cut that wire out and replaced it with one piece, from end to end, and with a new F-link. No more problems.
I didn't consider that the fusible link may in fact be burned open beneath its casing and hasn't been discovered yet. The melting at bulkhead connector does happen slowly /over a period of time. Maybe you fixed the visual flaw and not the fault. So much speculation. Good hunting
67Dart273
Well-Known Member
"Some things" to find the short
First, read the MAD article. Even if you end up "keeping" the ammeter, the diagram on their page gives a VERY good simplified view of primary power distribution:
http://www.madelectrical.com/electricaltech/amp-gauges.shtml
NOTICE that there are a few things (depending on year) that ARE NOT fused
Power to the headlight switch is not fused, although it has an internal breaker. However, it "might" be possible for the light switch to develop an internal short to ground.....to it's case
Likewise the power going TO the ignition switch is not fused, and also, the power FROM the switch to ignition, start, and bypass are not fused AT ALL
The alternator charging wire to the alternator (black) is not fused. THE ALTERNATOR could develop a short to ground
HOW TO FIND
All you guys should have the following:
Service manual and "your favorite" wiring diagram, a multimeter, 12V test lamp, spark tester, and "clip leads" (alligator clip wires)
In addition, a HEAVY 12V test lamp is sometimes useful. I've used an old headlight with one working filament, and like to use a stop / tail lamp socket. You can wire the two filaments together or separate to create a higher / lower wattage draw.
SO...........
Remove the battery ground. Take your "heavy" test lamp and wire from ground to the battery NEG terminal. Make sure EVERYTHING in the car is off.....dome and trunk lamps, key, everything.
It lights? No? Check the fuse link, it must be hooked up. Turn on the headlights if the lamp does NOT light, and turning them on should cause the lamp to light.
If the test lamp is NOT lit, you have no short, the fuse link is blown or the connection open
Once you have all that "working" if that's the word, the NEXT step is to actually try to eliminate the short.
FIRST thing I would do is to pull loose the alternator main charging wire. If that does not solve the problem, wiggle the ammeter connections, and disconnect them. Pull the two ammeter wires clear off the ammeter and hook them back together. If the short stays "away" you likely have a short right there "in" the ammeter
You can try pulling fuses, but if the fuse link blows, they likely are not the problem
First, read the MAD article. Even if you end up "keeping" the ammeter, the diagram on their page gives a VERY good simplified view of primary power distribution:
http://www.madelectrical.com/electricaltech/amp-gauges.shtml
NOTICE that there are a few things (depending on year) that ARE NOT fused
Power to the headlight switch is not fused, although it has an internal breaker. However, it "might" be possible for the light switch to develop an internal short to ground.....to it's case
Likewise the power going TO the ignition switch is not fused, and also, the power FROM the switch to ignition, start, and bypass are not fused AT ALL
The alternator charging wire to the alternator (black) is not fused. THE ALTERNATOR could develop a short to ground
HOW TO FIND
All you guys should have the following:
Service manual and "your favorite" wiring diagram, a multimeter, 12V test lamp, spark tester, and "clip leads" (alligator clip wires)
In addition, a HEAVY 12V test lamp is sometimes useful. I've used an old headlight with one working filament, and like to use a stop / tail lamp socket. You can wire the two filaments together or separate to create a higher / lower wattage draw.
SO...........
Remove the battery ground. Take your "heavy" test lamp and wire from ground to the battery NEG terminal. Make sure EVERYTHING in the car is off.....dome and trunk lamps, key, everything.
It lights? No? Check the fuse link, it must be hooked up. Turn on the headlights if the lamp does NOT light, and turning them on should cause the lamp to light.
If the test lamp is NOT lit, you have no short, the fuse link is blown or the connection open
Once you have all that "working" if that's the word, the NEXT step is to actually try to eliminate the short.
FIRST thing I would do is to pull loose the alternator main charging wire. If that does not solve the problem, wiggle the ammeter connections, and disconnect them. Pull the two ammeter wires clear off the ammeter and hook them back together. If the short stays "away" you likely have a short right there "in" the ammeter
You can try pulling fuses, but if the fuse link blows, they likely are not the problem
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