No headlights, fusible link at bulkhead melted…

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Three Forty Swinger

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Hello,

trying to do some detective work after my headlights stopped working last week. In so doing I discovered the fusible link between the starter relay and bulkhead connector terminal J is melted, the red wire on the inside of the bulkhead looks good, I haven’t looked up under the dash at the ammeter connections just yet.
Prior to noticing the fusible link I had dropped the headlight switch down and gained access to the floor dimmer switch, there is power at the H terminal light green wire on the hd switch and also at the dimmer switch center terminal, but nothing beyond so I thought it might be a faulty dimmer, but when I remove the connector at the dimmer and jumper from the power coming in to either of the other terminals it instantly loses power from the hd switch, if I disconnect and turn the headlight switch off and on again power returns at the switches H terminal… so no load on the circuit it seems to have power, the second I try to jumper either the high or low beams the switch breaks the circuit. I know there’s a few things going on here and they may or may not be related, just looking for assistance in cleaning things up, thanks!

Heath
 
The fuse link should pretty much kill ALL power into the interior. That is in the main battery feed to the ammeter.

You need to find out WHY

One way to not burn the car down is to find an old headlamp, or stop/ tail lamp socket, and wire an 1157 or headlamp in series with the main battery ground. They you can pull fuses, and the lamp will light if there is a load turned on, or a short, and will protect everything from being burned down

Do NOT forget the main charging wire from the alternator, and the alternator itself.

Remember, too, that the ammeter wires are red and black and BLACK IS NOT GROUND.

If you do not have a diagram or shop manual, run over to MyMopar.com and download a free service manual. You may have to sub Plymouth vs Dodge, etc.

Here is a simplified diagram from MADD Electrical concerning primary power

This varies year to year, but it shows the general plan. Power from the batt goes through the RED, fuse link, through the bulkhead connector, and to the ammeter. Through the ammeter, out on BLACK, and a few inches from the meter, a WELDED SPLICE branches off to feed the fuse panel hot buss, the key, the headlights ONLY power to the light switch.
amp-ga18.jpg
 
67Dart273 said:
The fuse link should pretty much kill ALL power into the interior. That is in the main battery feed to the ammeter.

You need to find out WHY

One way to not burn the car down is to find an old headlamp, or stop/ tail lamp socket, and wire an 1157 or headlamp in series with the main battery ground. They you can pull fuses, and the lamp will light if there is a load turned on, or a short, and will protect everything from being burned down

Do NOT forget the main charging wire from the alternator, and the alternator itself.

Remember, too, that the ammeter wires are red and black and BLACK IS NOT GROUND.

If you do not have a diagram or shop manual, run over to MyMopar.com and download a free service manual. You may have to sub Plymouth vs Dodge, etc.

Here is a simplified diagram from MADD Electrical concerning primary power

This varies year to year, but it shows the general plan. Power from the batt goes through the RED, fuse link, through the bulkhead connector, and to the ammeter. Through the ammeter, out on BLACK, and a few inches from the meter, a WELDED SPLICE branches off to feed the fuse panel hot buss, the key, the headlights ONLY power to the light switch.
View attachment 1716283351
Click to expand...

67Dart273 said:
The fuse link should pretty much kill ALL power into the interior. That is in the main battery feed to the ammeter.

You need to find out WHY

One way to not burn the car down is to find an old headlamp, or stop/ tail lamp socket, and wire an 1157 or headlamp in series with the main battery ground. They you can pull fuses, and the lamp will light if there is a load turned on, or a short, and will protect everything from being burned down

Do NOT forget the main charging wire from the alternator, and the alternator itself.

Remember, too, that the ammeter wires are red and black and BLACK IS NOT GROUND.

If you do not have a diagram or shop manual, run over to MyMopar.com and download a free service manual. You may have to sub Plymouth vs Dodge, etc.

Here is a simplified diagram from MADD Electrical concerning primary power

This varies year to year, but it shows the general plan. Power from the batt goes through the RED, fuse link, through the bulkhead connector, and to the ammeter. Through the ammeter, out on BLACK, and a few inches from the meter, a WELDED SPLICE branches off to feed the fuse panel hot buss, the key, the headlights ONLY power to the light switch.
View attachment 1716283351
Click to expand...

Thanks for the reply, I appreciate the simplified diagram, I do have a factory manual, but the wiring diagrams are far from straight forward…
As I continue to investigate, the main feed terminal at the alternator saw some heat as the plastic shield around the post is all melted, so I’m thinking the alternator may have been overcharging and did some damage, at no point did I notice the ammeter spike, but I don’t know how accurate they are in the first place…
So even with all the overheating, if I have power at the headlight switch there has to be another problem that’s keeping the lights from working, because if the welded splice off the main feed out of the ammeter was an issue, I wouldn’t see power at the headlight switch, or am I missing something? Thanks again!
 
I would DARN SURE check the alternator for a short!!!

I am thinking either the wiring has been hacked (modified) or you made a mistake, or maybe the link somehow made brief contact as you were wiggling stuff. You look at that diagram, here's how the headlights power works

Again, battery comes on the big RED to the fuse link, through the bulkhead connector, and to the ammeter. Through the ammeter, out the big BLACK, and a few inches away, the WELDED SPLICE. ONLY the headlight power comes off the welded splice, directly the the HL switch B1. The light switch has a breaker built in

Tail/ park/ instrument power comes from a fuse in the panel, which is fed through the welded splice to the fuse panel "hot" buss and the fuses that are hot at all times.
 
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The diagrams, some hints. Find the fuse panel, page 8-99, and look at the right side of the box marked "battery" the two on the buss. This is your panel hot buss, the stuff like brake lights, tail, hazard, that are always powered. Follow Q3-14R up and left. You will find the big splice we are calling the welded splice. You see R6A-12BK that is coming from the ammeter. If you are unaware, R6 or R6A is the circuit, 12 is the wire size, and BK is BlacK.

If you go up near the top of page 8-98, find the ammeter you will see that black, and on the left, A1-12R, which goes to J in the center group of the bulkhead connector. That is battery power coming inside from the fuse link, and should be the ONLY power coming in to the interior
 
Find the light switch about 1/4 of the way from the top of 8-99. B, or B1 at bottom left is the headlights only power Follow L1-16BK down and left it goes right to the welded splice
 
67Dart273 said:
This varies year to year, but it shows the general plan. Power from the batt goes through the RED, fuse link, through the bulkhead connector, and to the ammeter. Through the ammeter, out on BLACK, and a few inches from the meter, a WELDED SPLICE branches off to feed the fuse panel hot buss, the key, the headlights ONLY power to the light switch.
View attachment 1716283351
Click to expand...
Im not sure Im understanding the flow of current, you are saying that it flows from the battery through the red towards the interior, but the diagram shown here shows it flowing towards the battery, and the alternator supplying the current to the welded splice. I must be missing something basic here.
@67Dart273 not questioning you at all, just trying to learn :)
 
70SwingerGuy said:
Im not sure Im understanding the flow of current, you are saying that it flows from the battery through the red towards the interior, but the diagram shown here shows it flowing towards the battery, and the alternator supplying the current to the welded splice. I must be missing something basic here.
@67Dart273 not questioning you at all, just trying to learn :)
Click to expand...

I will definitely be checking the alternator as part of this entire repair… I’m thinking if the terminal on the alternator got that hot it’s indicative of a problem within the alternator. I am building a list of parts I’ll need to order besides the new fusible link, I’d like to figure out the headlight issue before hand with the car turned off and then figure out why the link and alternator show signs of excessive current…
I traced the path you described on the diagram in the manual and that all makes sense, I will try and work around the fusible link and try the headlights again, but I tried several times last night and the second I went from the light green wire at the center of the dimmer harness to either wire powering the high and low beams my test light at the headlight switch would go out, disconnect the jumper, cycle the headlight switch and the test light would light up and stay lit until I tried to jumper at the dimmer harness… could the circuit breaker in the headlight switch just be tired? It doesn’t make sense to me that there would be a short on both the high and low beams? Plenty to think through, thanks for your insight so far!
 
70SwingerGuy said:
Im not sure Im understanding the flow of current, you are saying that it flows from the battery through the red towards the interior, but the diagram shown here shows it flowing towards the battery, and the alternator supplying the current to the welded splice. I must be missing something basic here.
@67Dart273 not questioning you at all, just trying to learn :)
Click to expand...
Current flow is most commonly thought of as "electron flow" so yes, neg to pos. But for explanation it is often simpler to start at the battery and work from there. The functional path, whichever current flows, LOL

And the diagram does not follow, either, because they are showing current from the alternator, and the from the welded splice to accessories. So the shown current flow is ambiguous. The main thing is to follow the path like a road.

And to make it more complicated, the ammeter can flow both ways. When the battery is supplying current because either the engine is off or the alternator is running to slow to keep up, the ammeter will show discharge, but when the battery is charging, current flow in the battery / alternator relationship will be in reverse.

Current (electron) flow from any load, such as lights, will always "actually" be from battery neg---to body ground---to harness grounding wire---through headlights---through dimmer switch---through HL switch----to welded splice---to ammeter---and if alternator is more positive (charging) that battery to alternator and back to ground and all over. If alternator is not putting out, then current will end up at batter +
 
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