73 Duster crank but no start / blowing in-line fuse on red ignition wire

[GoldDuster727]

Hello, all!

I’m new to the forum, and per everyone’s guidance, I’ll post my issue here. I just bought a 1973 Duster last Monday, started driving it home for about half an hour on the highway, then it backfired and died, and wouldn’t crank/start. I had it towed home. After opening the hood, I noticed that the ignition module was cooked, and the potting ran down the inner fender.

I was able to trace the cranking issue back to under the dash where someone added an in-line, 30a fuse on the red ignition wire. After replacing the fuse, the car will crank, but if I leave the key in the “on” position, it will blow the fuse after a second or two.

My gut feeling, and my brother-in-law ‘s (mechanic, coming over shortly to help me track this issue down) opinion is that something’s drawing hard on this wire, and/or there’s a short somewhere.

I pulled the ballast resistor, and it is cracked up, so I just replaced that.

Any guidance on where to look next is much appreciated! We are checking out the bulkhead connection at the moment.

 

[67Dart273]

What do you mean by "red ignition wire?"

These cars have a fuse link in the big red ammeter wire carrying battery power from the engine bay into the bulkhead connector and on into the ammeter and for power into the interior.

If someone hacked that with a fuse, and if that is the wire you are looking at, 30 is not enough. It must be at least as big as the rating of the alternator.

If you do not have a service manual or wiring diagram, run over to MyMopar.com, and download a service manual for free. Also go to the wiring section over there and download the aftermarket wiring diagrams. CAVEAT: These leave out details, but can be easier to follow. I use both the factory ones and the 2 page aftermarket ones.

Cooked potting on these modules does not automatically indicate a problem. The potting deteriorates, nobody knows how old that one is, and underhood heat from the engine can be enough to cause it to drip and run. Also leaving the key "on" when the engine is not running is not good, as the ignition ALWAYS draws current through the coil and module with key left "in run."

Also here is an article about the problems with the charging/ ammeter/ bulkhead connector circuit. I'm not suggesting you jump right into this, but two things:
1....This explains the problem, and alerts you a bit
2....The simplified diagram there is good to show how the primary power works

Catalog

Functionally, main power comes from the battery (RED) runs through the fuse link, through the bulkhead / firewall connector, and to and through the ammeter.

Comes off the ammeter on big BLACK to the welded splice which is a few inches from the ammeter under the dash. This splice branches off as shown to feed the fuse panel "hot" buss, feeds headlights only power to the HL switch, feeds power to the ignition switch.

This varies a bit depending on year/ model

 

[Daves69]

FWIW, the potting material in some ECUs can deteriorate over time and leach out on their own. Opens the possibility of shorting out.
Here's one I had in a box for a long time and what it looked like several years ago after I "unstuck" from the cardboard...........

For kicks I put it in a plastic bag. What it looks like today..........

MyMopar has a '73 Dodge FSM free to download which may be useful if you don't have one.

Service Manuals – MyMopar

mymopar.com

 

[GoldDuster727]

What do you mean by "red ignition wire?"

These cars have a fuse link in the big red ammeter wire carrying battery power from the engine bay into the bulkhead connector and on into the ammeter and for power into the interior.

If someone hacked that with a fuse, and if that is the wire you are looking at, 30 is not enough. It must be at least as big as the rating of the alternator.

If you do not have a service manual or wiring diagram, run over to MyMopar.com, and download a service manual for free. Also go to the wiring section over there and download the aftermarket wiring diagrams. CAVEAT: These leave out details, but can be easier to follow. I use both the factory ones and the 2 page aftermarket ones.

Cooked potting on these modules does not automatically indicate a problem. The potting deteriorates, nobody knows how old that one is, and underhood heat from the engine can be enough to cause it to drip and run. Also leaving the key "on" when the engine is not running is not good, as the ignition ALWAYS draws current through the coil and module with key left "in run."

Also here is an article about the problems with the charging/ ammeter/ bulkhead connector circuit. I'm not suggesting you jump right into this, but two things:
1....This explains the problem, and alerts you a bit
2....The simplified diagram there is good to show how the primary power works

http://[URL]http://www.madelectrical.com/electricaltech/amp-gauges.shtml

[/URL]

Functionally, main power comes from the battery (RED) runs through the fuse link, through the bulkhead / firewall connector, and to and through the ammeter.

Comes off the ammeter on big BLACK to the welded splice which is a few inches from the ammeter under the dash. This splice branches off as shown to feed the fuse panel "hot" buss, feeds headlights only power to the HL switch, feeds power to the ignition switch.

This varies a bit depending on year/ model

View attachment 1716275890

Hey, 67dart.. thanks SO much for the info and the diagram. I saw some of your explanations on other posts as well. This was super helpful!

We tracked the issue down, and now I have a couple questions. The issue is with the alternator. We unhooked it completely and got the car to run off the battery without smoking any wires and without blowing the fuse.

I don’t know if you can see in the pictures I posted, but is this style that was installed the wrong one? We are wondering if this one either failed, or if it needs to be internally regulated or not. Any insights are much appreciated. Thanks again!

 

[GoldDuster727]

FWIW, the potting material in some ECUs can deteriorate over time and leach out on their own. Opens the possibility of shorting out.
Here's one I had in a box for a long time and what it looked like several years ago after I "unstuck" from the cardboard...........
View attachment 1716275880

For kicks I put it in a plastic bag. What it looks like today..........

View attachment 1716275883

MyMopar has a '73 Dodge FSM free to download which may be useful if you don't have one.

http://[URL]https://mymopar.com/service-manuals/

[/URL]

FWIW, the potting material in some ECUs can deteriorate over time and leach out on their own. Opens the possibility of shorting out.
Here's one I had in a box for a long time and what it looked like several years ago after I "unstuck" from the cardboard...........
View attachment 1716275880

For kicks I put it in a plastic bag. What it looks like today..........

View attachment 1716275883

MyMopar has a '73 Dodge FSM free to download which may be useful if you don't have one.

http://[URL]https://mymopar.com/service-manuals/

[/URL]

lol whoa! That’s wild that it just breaks down like that on its own but I guess it makes sense.

And thank you for posting that FSM! I will start referring to that.

 

[67Dart273]

Hey, 67dart.. thanks SO much for the info and the diagram. I saw some of your explanations on other posts as well. This was super helpful!

We tracked the issue down, and now I have a couple questions. The issue is with the alternator. We unhooked it completely and got the car to run off the battery without smoking any wires and without blowing the fuse.

I don’t know if you can see in the pictures I posted, but is this style that was installed the wrong one? We are wondering if this one either failed, or if it needs to be internally regulated or not. Any insights are much appreciated. Thanks again!

I missed something, do not see an alternator. Should have the later 70/ later style with the flat electronic regulator. You can check quick if it is locked into charge by watching the ammeter, with it charging. Disconnect the green wire at the alternator and see if it quits charging.

I still don't know what that fuse does. Does that fuse kill the headlights as well? Hard to say

 

[GoldDuster727]

I missed something, do not see an alternator. Should have the later 70/ later style with the flat electronic regulator. You can check quick if it is locked into charge by watching the ammeter, with it charging. Disconnect the green wire at the alternator and see if it quits charging.

I still don't know what that fuse does. Does that fuse kill the headlights as well? Hard to say

I’m right there with you. I think the fuse is to protect the bulkhead connector? Not sure.. But that’s great info for the alternator. Thanks so much.. here’s the pictures of the alternator that’s installed attached. I thought I uploaded these, but I guess they didn’t make it. Per my brother in law, I will also be replacing those belts.