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One Terminal Melted in Firewall Junction Block

Mocktwo

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I have no power in my 72 Challenger anywhere. Seems the previous owner didn't put in a fuseable link and a surge melted the primary red wire going from the starter relay to the ammeter at the firewall junction block. Any suggestions on how to fix this? Can single terminats be replaced?

Firewall Connector.jpg


Firewall Juntion Block.jpg
 

Chryco Psycho

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Yes you can replace single terminals , with correct ones , the male tab has to be squeezed from the side to release it , the female has a small tag holding it into the nylon connector
 

Mocktwo

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Thanks both. I'll dig deeper into it today.
Would you know the size for a fuseable link at the starter relay? (no AC)
 

Challenger RTA

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From radio cuts out. this might help.just seen your post

1 Jiggled + cables. Did anything else work? light horn radio? 2 driving back home the radio cut out. any thing else cut out? 3 you were meant the alt gauge right. alternator didnt budge. Off hand I believe the headlight power comes from the black wire splice alt gauge under dash.The black wire goes to the firewall connection then to the alt. which in turn connects to the alt gauge the to the red wire to the firewall connection,then to the battery. OK lets say the alt is good,because the light work and it is on the alt side of amp gauge. understand batt side of amp gauge RED is hot all the time.and feeds power to alt to excite the field. Only takes very little voltage to start to charge not amps.once running alt feeds batt and other. power can go both ways. I would check red and black firewall connection 12 gauge wire. you might find them burnt. the alt wires check them too. I eliminated the amp gauge all together and use firewall connections black and red to feed inside. Get a plug in a voltage gauge to lighter. I believe this is correct if not someone will say or I will correct it. What I did was replace fuse box and bulk head connector. cleaned ever or repaired ever connection on the car. splice one under dash that is black and alt,removed headlight and horn. horn now with flasher fuse headlight on console fuse.will do headlight relay set up later to remove high cuurent for inside. Reused Red [from batt] and Black[ ACC ]wire as original Ran an other 12 gauge red wire with fuseable link that is 16 gauge to starer relay and use alt firewall connection for a 2nd power feed. Will use an 8 gauge directly to battery. When cutting splice one it also cut power to steering column Acc. solution use acc connection front or back of fuse box.​


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Mocktwo

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No power at the ammeter red wire. Power on the battery side of the bulkhead connector. Thus the bulkhead connection is bad and based on the melted firewall side ...
I am going to run a 8 gauge wire (with a fusible link) directly to the ammerter bypassing the bulkhead to verify this is the issue. I'll update this post with the results.
 

Challenger RTA

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8 gauge my be a little over kill.
Wire size current table:
18 gauge wire = 5-8 amps
16 gauge wire = 10-12 amps
14 gauge wire = 15-17 amps
12 gauge wire = 20-25 amps
10 gauge wire = 30-40 amps
8 gauge wire = 50-60 amps.

Fusible link colors
Link Gauge Color
20 Gauge Blue
18 Gauge Brown or Red
16 Gauge Black or Orange
14 Gauge Green
12 Gauge Gray


Keep in mind that the wire size in the chart is for the circuit itself, not the size of the fuse link. The packages of fuse link repair material you can get at the auto parts stores also will have a current rating on them. 12 or 10 gauge should work depending on acc. don't know what the amp gauge is rater for.8 gauge is what I ran from alt to battery. may put an additional power block by battery.could also run down to starter connection. I have the original alt 45 amps? Put a 60 amp on for now.trying to get the 80 amp rebuild kit from Quick Start.out of stock I would rather be criticized for the wire than a crispy car.In a few years a new harness will have the same problems. It was a bad design from the start. It would be nice if someone made a direct replacement voltage gauge.

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budascuda

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Nothing is like a new harness for a 40 thousand Dollar car!
 

budascuda

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If everything is as they should be, then all is well, but if there is a problem somewhere, other than old connectors, the new harness will be cooked too.
I am gonna use this saying which I hate, but seems appropriate here;
When it comes to electricals, "You gotta consider the holistic approach"
I know it sounds pompous, but it puts it in a nutshell.
I have also seen comments about changing the ammeter to a Volt meter and doing away with that much current going through the system, but other members who are knowledgeable in that area can definitely help you.
At any rate, the best of luck!
 

Mocktwo

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Thanks all for your help and comments. Challenger RTA - I agree, criticize my non-burnt wire, so I went with 8 gauge.
budascuda and moparleo, I ran a new independent wire to the dash and eliminated the Ammeter. Also I put in a 16 gauge fusible link which should have been there when it was originally rewired. Better safe than sorry. My Challenger is a driver, not a restoration. I could understand wanting more authentic if this were a restoration. moparleo, I appreciated the documents which I have mostly implemented, but I decided to run the primary red wire through another hole in the firewall and not drill out the bulkhead connector.

Now the next quandary ... with the dash apart, do I upgrade to an aftermarket Rallye cluster? The fun never ends :eek:)
 

Mocktwo

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My understanding is there are devices on the black side of the Ammeter that still need to be powered (Ignition switch, Light Switch, Fuse Box). All I'm doing is removing the Ammeter from the circuit, not rerouting the standard wiring harness flow. A potential second step would be to reroute the Alternator directly to the battery and then feed the dashboard wiring harness through the original black wire through the firewall. I'm hesitant as that messes with the colour coding of current flow.

Factory Wiring.jpg
 

moparroy

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I guess that is what I was getting at - if you run a wire large enough to carry the required service current through the firewall, you don't need to run the heavy charge current wire through the firewall twice - remember the charging current which is the larger part (especially if the battery gets depleted) - not only runs through the firewall to the ammeter on the black wire in your diagram but also runs out again to the engine bay through the firewall on the red wire. I fixed the original pins on mine - required replacing the bulkhead connector inside part as well - then ran a completely parallel ammeter bypass all within the engine bay. Well that's the mods I made on the wire harness - its not installed yet and the ammeter will be useless but that's fine - bought a small accessory plug voltmeter. It looks like from your original pics the problem is on the red wire back out judging on the slightly offset terminal - that one was worse on mine too.

I found the wire color on these harnesses to be less than perfect anyway - the welded splice you show has 3 black wires and 3 red wires connected together according to my '74 FWM wiring diagram. To me the first mistake is using black for a positive side wire anywhere - I believe I marked all mine with red heat shrink. Originality be damned - I want to know when I am dealing with positive side voltage - nearly blew off a finger that way once.
 

moparleo

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Replacement wiring has nothing to do with looks. The YearOne and M & H harnesses use the factory connectors and match the factory wiring diagrams. All wiring deteriorates with age and the connections oxidize with age as well. The biggest headache with older cars is always in the wiring.
Whether it is in the engine compartment or the lighting ( headlamps, directional's, tail/brake lights etc...)
Grounds #1. Starting new will eliminate years of chasing your tail.
Consider what 1970 electrical technology was compared to now.
Cell phones, bluetooth, monster amps, high output charging systems, and on and on.
Connect that all up ,to 50 year old, burnt wiring.
Not me.
 

Mocktwo

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Moparleo and Moparroy, fundamentally I agree with you, but I'm going slow. First objective was to get my car running again so I can drive and enjoy it. In that first objective was to get rid of the major fail point - Ammeter & Firewall connection (mine was the burnt red wire). I know my engine wiring harness needs to be replaced and I would be in favour of beefing up the alternator connection and removing that from the firewall also. I just have to get my head around it. Its been 45 years since I messed with mopar wiring and in my old age I don't want my car to defibrillate me :eek:)
 

Challenger RTA

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You ask : If you are bypassing the ammeter why does the wire need to go through the firewall at all? It doesn't. the alt need only a few volts to excite to charge. The black wire from the alt is the charging the battery. Use it as 2nd fuseable link power source accessory power. you have to think a black as accessory and red as battery power supply always hot. some blacks could always be hot all hot when ign on. don't think of it as red+ black - ! A stock alt 45-50amp through a 12 gauge wire rated at 20-25 amps. Then install a 60 or 100 amp alt on a 12 gauge wire? The chart below shows 12AWG is yellow in the chart. voltage drop not to relevant for very short runs. the connection are realy the bad point the don't carry the load even when new.
 

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Mocktwo

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So you are suggesting Alternator directly (with fusible link) to the starter relay (Ie. battery) and then to get power into the dash I could use the original alternator black wire by connecting the red wire to it. Thus the high amps of the alternator (to charge the battery) would not flow through the firewall and only device load in the dash.

The earlier diagram from moparleo seemed to have the red wire and alternator black wire in parallel, thus one of them really isn't needed.

Wiring - Without Ammeter.jpg
 

Challenger RTA

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This is what I did. you don't have to do it.This way it gives you two 20 -25 amp circuits. I also eliminated the power feed for the headlights,from the splice and fused from fuse box. the headlight originally don't have a fuse. later I will do a headlight relay circuit. That will remove another high current draw from inside. there are other issues of person preference looking to resolve.

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