Problem finding electrical short

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Super-Cuda

MOPAR .. Move Over, Plymouth Approaching Rapidly!
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Hey guys,

I have a short in my wiring harness in my 68 Cuda. New M&H wiring harness. modified for electronic ignition and ammeter replaced with voltmeter in the guage cluster. Ammeter wires were butt connected and soldered. Short is present in the red wire that runs from main post of the starter relay to the bulkhead connector. I have removed the fuses one by one, disconnected the rear tail lamp harness, the dash cluster wiring, ignition switch, headlamp switch, flasher units and flasher switch, wiper switch, console harness, and the door switches. Also dropped the fuse panel and didn't see anything wrong there either. The battery is fully charged and load tested. Everything was working fine and suddenly, the interior lights started flickering. . I can see most of the harness but there doesn't seem to be any cuts or damage to it..
Any help would be greatly appreciated. Thanks guys.
 
Starter relay ?
I'd guess about 75 ohms on the coil.
Normally open contacts.
Thanks for the reply Dfr360cuda, Im back at it tomorrow so Ill definitely check that!
 
Define "short." Is it sparking badly, AKA drawing a lot of current?

Or is it a "poor connection" AKA your dome light lights dimly, goes out, etc?

Very very first thing I'd suspect is the fuse link/ bulkhead connector

It's very useful to refer to the simplified MAD diagram on their modification page, as it has a simplified diagram of the main power distro

Catalog

amp-ga18.jpg


Another good candidate for a short (high current) is the alternator output connection. It is normally no 12 or 10 black with a ring terminal. You may have forgotten it, or there may be something wrong with your alternator
 
Define "short." Is it sparking badly, AKA drawing a lot of current?

Or is it a "poor connection" AKA your dome light lights dimly, goes out, etc?

Very very first thing I'd suspect is the fuse link/ bulkhead connector

It's very useful to refer to the simplified MAD diagram on their modification page, as it has a simplified diagram of the main power distro

Catalog

View attachment 1715098749

Another good candidate for a short (high current) is the alternator output connection. It is normally no 12 or 10 black with a ring terminal. You may have forgotten it, or there may be something wrong with your alternator
Hey 67Dart273,
I have unplugged everything I can from the harness, all the switches, courtesy lamps, headlamp harness, rear tail light harness, console harness in an effort to remove as many possibilities of the short cause as I can . When I touch the ring terminal from the red wire going to the fusable link on the bulkhead connector(engine side) to the starter solenoid post I get a very small arc.
I really appreciate your input. Thanks!!
 
Just general info here that may not be related to your issue. When the charging system develops a fault the evidence is often seen in the light bulbs.
Last time my voltage regulator suddenly developed a fault, the evidence I noticed was volt gauge needle started twitching. I might have noticed flickering lights also had it been night and lights on. Short circuits can occur inside alternators too. Depending on how its wired, the alternator could be where your arc is coming from.
 
Just general info here that may not be related to your issue. When the charging system develops a fault the evidence is often seen in the light bulbs.
Last time my voltage regulator suddenly developed a fault, the evidence I noticed was volt gauge needle started twitching. I might have noticed flickering lights also had it been night and lights on. Short circuits can occur inside alternators too. Depending on how its wired, the alternator could be where your arc is coming from.
Thanks for the reply Redfish,
I 'm pretty sure its not the regulator (electronic) as the short is there without the vehicle running and with the alternator wiring disconnected. I will make sure the regulator is disconnected as well though as I check.
Thanks for the suggestion though and please let me know if you think of any other possibilities. Really appreciate the response!!
 
Hey 67Dart273,
I have unplugged everything I can from the harness, all the switches, courtesy lamps, headlamp harness, rear tail light harness, console harness in an effort to remove as many possibilities of the short cause as I can . When I touch the ring terminal from the red wire going to the fusable link on the bulkhead connector(engine side) to the starter solenoid post I get a very small arc.
I really appreciate your input. Thanks!!

Let me get this clear..........

New dash harness and you have most everything disconnected under the dash?

Is the cluster connected?
Ignition switch?
etc? What else?

And obviously you have the bulkhead connector connected

Can you wire a test lamp or maybe a tail lamp in series with the fuse link? How bright does it glow? If none, but a smaller wattage 12V test lamp in there. Any glow? If the lamps don't glow very bright take your meter CAREFULLY set it up for current and measure how much current is actually flowing

Post a photo of your meter or at least the brand / model we should be able to help you with that if needed
 
Let me get this clear..........

New dash harness and you have most everything disconnected under the dash?

Is the cluster connected?
Ignition switch?
etc? What else?

And obviously you have the bulkhead connector connected

Can you wire a test lamp or maybe a tail lamp in series with the fuse link? How bright does it glow? If none, but a smaller wattage 12V test lamp in there. Any glow? If the lamps don't glow very bright take your meter CAREFULLY set it up for current and measure how much current is actually flowing

Post a photo of your meter or at least the brand / model we should be able to help you with that if needed
 
Thanks for the info/instructions 67Dart273. Man what a wacky problem I'm having! I took the bulkhead connectors out of the firewall completely and metered (continuity & short check between conductors ) every wire, all checked ok. then I removed & metered the ignition switch ,the emergency flasher switch and the wiper motor switch. All ok. I am going to get an ammeter tomorrow and perform the current check you suggested. I'm now down to the headlamp switch that looks suspect. The resistive coil inside the white circular wheel is bunching up and the switch is not rotating properly. after reassembling the wiring harness and components, the short was still there . When I removed the headlamp switch, the short disappeared. Hopefully I'm on to something here so maybe a new headlamp switch is in order. What do you suggest? Is there any particular aftermarket replacement switch you could recommend ? Current one is an original mopar switch, p/n 2820782.
 
The headlight dimmer switch switches the headlight power between high and lo beams. It also mounted on floor, sometimes it fails, and a short to ground happens. As a second check, disconnect the switch 3 wire cable and see if short goes away.
 
The headlight dimmer switch switches the headlight power between high and lo beams. It also mounted on floor, sometimes it fails, and a short to ground happens. As a second check, disconnect the switch 3 wire cable and see if short goes away.
Thanks for the reply KitCarlson.
This was one of the first things I tried as I removed each connector from the harness to locate the short.
Thanks again and please let me know if you think of anything else. This is a weird one for sure!!
 
I'm now down to the headlamp switch that looks suspect. .

The coil if you are unaware is for the dash lamp dimmer. Make sure the switch is not rotated "all the way" to the left which activates the dome lights

Those are common switches. Many parts stores still stock them, they fit "push pull" mopars for many years
 
The coil if you are unaware is for the dash lamp dimmer. Make sure the switch is not rotated "all the way" to the left which activates the dome lights

Those are common switches. Many parts stores still stock them, they fit "push pull" mopars for many years
Thanks 67Dart273 for taking the time to help me out. Hopefully the switch will solve my problem. Ill post a reply if it works.
 
Ok guys so I finally found the problem! When I changed the ammeter to a volt meter in the rallye gauge cluster, the positive terminal of the volt meter was making intermittent contact with the gauge housing , shorting the whole electrical system out. I finally discovered it after removing the complete gauge cluster and checking all the connections for shorts. I fixed the problem by covering the positive terminal with double wall heat shrink tubing. Electrical system now works perfect. Unfortunately, I ruined a brand new battery (now has dead cells) and the relays in my new Daniel Stern lighting system are also fried. Oh well, can't do anything about it now so ... moving on.
Many thanks to all the A-Body members who tried to help me to solve this problem ,Greatly appreciated!!!
 
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