69 Cuda wiring problem

69 M-CODE CUDA

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I’m doing a basic stock restoration on my 69 Cuda, and am having some electrical issues I’m unsure of.
I did the Mad Max (or whatever) modification that bypasses the bulkhead connectors and disconnects the amp gauge in the dash. I used the recommended wire gauge, the two fusible links, and soldered crimp connections, etc.

The problem I’m having is that after reinstalling the dash, I’m getting a small charge through the circuit that the dash lights/console light are using, even when the ignition and light switch are off. When I turn the light switch on, they all get brighter per normal, but remain partially on when switched off.
A couple things to note is that I haven’t yet installed headlights, backup lights or tail lights, so my thought was it could be a ground issue there? Also I’m using LED bulbs in the dash, for what it’s worth.

Any ideas where to start troubleshooting? I really appreciate the help.

Thanks, Doug
 

Professor Fate

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When you say you haven't installed the headlights, backup or taillights yet, are you referring to just the bulbs, or that you don't have the harnesses completely hooked up yet? If the latter, get the grounds (at a minimum) of those harnesses hooked up and WELL grounded, and try again- no grounds in those harnesses could be causing a weird "feedback" type issue...
 

Mike69cuda

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Does this happen with the doors open or closed (one way and not the other) by any chance? Since the dome light switches the ground instead switching the positive, weird things can happen if you lose grounds.
 

69 M-CODE CUDA

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All of my ground wires are installed, but not the bulbs.

Tomorrow I’m going to go ahead and install all the lights all over, and see what happens.
 

67Dart273

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I’m doing a basic stock restoration on my 69 Cuda, and am having some electrical issues I’m unsure of.
I did the Mad Max (or whatever) modification that bypasses the bulkhead connectors and disconnects the amp gauge in the dash. I used the recommended wire gauge, the two fusible links, and soldered crimp connections, etc.

The problem I’m having is that after reinstalling the dash, I’m getting a small charge through the circuit that the dash lights/console light are using, even when the ignition and light switch are off. When I turn the light switch on, they all get brighter per normal, but remain partially on when switched off.
A couple things to note is that I haven’t yet installed headlights, backup lights or tail lights, so my thought was it could be a ground issue there? Also I’m using LED bulbs in the dash, for what it’s worth.

Any ideas where to start troubleshooting? I really appreciate the help.


Thanks, Doug

This sounds like some sort of backfeed. First step is to locate the inst fuse in the fuse box which will be at one end of the box. Pull that fuse. Look at the lamps and see if they are out. Take a meter and be SURE the meter is grounded. Measure BOTH sides of the fuse clips with the fuse out. Normally, this should be dead. I am betting the "bulb" side is hot.

The dash lamp circuit should ONLY be hot under the following conditions, and how it works

First the light switch has TWO power sources, one of which is NOT fused and comes from the black ammeter wire in the harness. This powers ONLY the head lights

The second comes from the tail fuse and powers the tail/ park and dimmer controlled dash lamps

With that circuit intact, and the light switch on, power goes through the dimmer control, out the tan wire and TO the INST fuse. From the fuse, out to all dimmer controlled dash lamps on orange wires

So the tail fuse/ circuit must work, the lamp switch must be in park/ head, and the dimmer control must be twisted "some to the left."

It might be that the cluster/ pc board is not actually grounded, and is seeing a voltage source, I don't know what "yet"
 

69 M-CODE CUDA

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This sounds like some sort of backfeed. First step is to locate the inst fuse in the fuse box which will be at one end of the box. Pull that fuse. Look at the lamps and see if they are out. Take a meter and be SURE the meter is grounded. Measure BOTH sides of the fuse clips with the fuse out. Normally, this should be dead. I am betting the "bulb" side is hot.

You’re right, that bulb side of the instrument lamp fuse is 12V.

So I installed the headlights, parking lights and tail lights, and everything seems to work correctly, with the exception of the turn signals. Where the heck is the flasher? I found the emergency flasher, but can’t seem to locate the turn signal flasher.
I appreciate the detailed help with this. This forum is the best.
 

1969383S

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My Opinion, I know it does not mater but! You are going to get it.

The Mad Bypass is so far from stock. It is "Absolutely" not needed for a "Stock" resto. You have an "M" code you say. I would not even consider these mods! Fix all the bad deals done to this vehicle over the years and enjoy it. I did and much Happy for doing it!
 

1969383S

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I drove by Year One today and thought to myself, someone on A-bodies needs a new Harness!
 

67Dart273

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My Opinion, I know it does not mater but! You are going to get it.

The Mad Bypass is so far from stock. It is "Absolutely" not needed for a "Stock" resto. You have an "M" code you say. I would not even consider these mods! Fix all the bad deals done to this vehicle over the years and enjoy it. I did and much Happy for doing it!

This all depends on "whut." If you have some large accessories, like a great big stereo, and or a GREAT big alternator (more than say, 45A) then the stock system is inadequate. In the 70's I had a 6bbl RR. It did have "some stuff." Aircraft landing lights (intermittent high speed driving lights) and some amateur radio gear. Melted the crap out of the bulkhead connector. So this was a car that was in S CA no rust, and quite new. And yet..............

Now extrapolate that to a 50 year old car...................
 

67Dart273

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My own 67 Dart, which was "bone stock" and likely a 37A alternator, was showing signs of "meltage" in the bulkhead connector. It had 1.7V of drop from the battery to the VR IGN terminal. This causes the battery to charge at 14+1.7 nearly 16V
 

1969383S

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This all depends on "whut." If you have some large accessories, like a great big stereo, and or a GREAT big alternator (more than say, 45A) then the stock system is inadequate. In the 70's I had a 6bbl RR. It did have "some stuff." Aircraft landing lights (intermittent high speed driving lights) and some amateur radio gear. Melted the crap out of the bulkhead connector. So this was a car that was in S CA no rust, and quite new. And yet..............

Now extrapolate that to a 50 year old car...................

Based on a Stock resto, nothing more! These cars were just fine when new as such! JMO
 

1969383S

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My own 67 Dart, which was "bone stock" and likely a 37A alternator, was showing signs of "meltage" in the bulkhead connector. It had 1.7V of drop from the battery to the VR IGN terminal. This causes the battery to charge at 14+1.7 nearly 16V

We know that eventually they all will. Thus the new harnesses. They are 50+ years old right?
 

MrJLR

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I am just curious for the reason for the "Mad Max" wiring bypass.
So you aren't running full amperage through the firewall and amp gauge and causing a potential fire...
A voltage gauge is all you really need.

Jeff
 

Mattax

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So you aren't running full amperage through the firewall and amp gauge and causing a potential fire...
A voltage gauge is all you really need.

Jeff
That's what they claim.
Not the full picture and neither an ammeter nor a voltmeter provide the full story.
 

69 M-CODE CUDA

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So I’ve installed all of the lights inside and out and everything works correctly, except the turn signals and emergency flasher. I’m using modern hi-power leds in these locations. Can that have anything to do with it? Thanks for the help.
 

Professor Fate

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So I’ve installed all of the lights inside and out and everything works correctly, except the turn signals and emergency flasher. I’m using modern hi-power leds in these locations. Can that have anything to do with it? Thanks for the help.
There you go. LEDs need electronic flashers (identified by a separate pigtail on the flasher unit that goes to ground) in order to work. Search the electrical threads for part numbers and recommendations.
 

1969383S

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Reducing any load on these old systems is smart! I left mine stock and concentrated on other areas, like the opera lights and other interior items.
 

Professor Fate

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Also keep in mind that some LEDs have polarity- a distinct pos. and neg. Bulbs such as your dash lights can be installed in a reversed polarity and not function...
No, "reversing the polarity" does NOT make the warp drive faster, Scotty...
 

1969383S

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4 amps alone on the opera lights. Simple smart approaches work. Special flashers and such, I stayed away from. Opinion only, but reducing load is very smart even with 100% new harnesses!
 

67Dart273

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I am just curious for the reason for the "Mad Max" wiring bypass.

Because ALL the alternator output current goes into the passenger compartment through the bulkhead connector on the big black wire, and must pass through what amounts to a 1/4" flag terminal, then back OUT through an identical terminal on the way back to the battery. The black terminal especially is under heavy load, "let's say" a cold winter day, you maybe had a bit of trouble starting the car, the battery is low, you are on the road to work running the radio, the lights, the heater, etc, so the alternator is running "full tilt" to recharge the battery, run the lights and other accessories. MANY of these become damaged, some beyond function.

My first experience was in the early 70's with my 70 440-6 Roadrunner. I ended up drilling out the bulkhead connector for those terminals, and running solid wire through them. This obviously was before Al Gore invented the internet

The problem is amplified because how old? are these girls? And folks put heavier output alternators on them, as well as added accessories like Great Big stereos, electric pumps and fans, and ??
 
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