Chasing a parasitic drain on the ammeter circuit

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RBConvert said:
Going back to my original post, the DMM fluctuates between .3 and .6A. The test light also flickers, not on and off, but dimmer and brighter. So the draw is pulsating. First thought would be the horn relay, but its disconnected. The voltage limiter on the PCB is an electronic unit from RTE.
I don't have a lot of experience chasing down parasitic drains so I don't know if a pulsating draw is common or if its a clue to identifying the culprit.
Click to expand...
Wait a minute. Is this key on or key off? There is very very little in the car that can pulsate. Is it "even" or erratic? Pull the 4 way flasher unit. Does it have a clock? And have you checked for aftermarket stuff like an old alarm, etc?

You need to disconnect the ign switch right at the switch, to find out if there is something wrong internally

And find out if the switch had a "key in" light. There is a timer deal, small cylindrical device with 3 terminals. That would be a suspect.
 
Pg 8-112 of the 69 Dart manual. Look for the "Starter and ignition switch time delay relay"

keyinrelay.jpg
 
Mattax said:
IDK. Maybe you got this covered but skimming this again now, maybe not.

These cars are not fused like a house. A lot of circuits are unfused. There are various reasons why which we don't need to spend time on now. Point is that pulling fuses only gets so far.

No clock or convertible top, with the key off, we can eliminate everything on the run and start circuits.
View attachment 1716424915

We can also eliminate everything on the switched accessory circuit, headlights and parking unless there is a fault in a switch.
View attachment 1716424917


Any others I'm missing?
Click to expand...

Headlite switch grounds to activate interior/dome lites .
I mentioned unplugging headlite switch .
 
Inertia said:
Headlite switch grounds to activate interior/dome lites .
I mentioned unplugging headlite switch .
Click to expand...
So do the door switches. The dome light is powered through a fuse. Removing the fuse didn't stop the mystery current.
Suppose its possible there is a weak short in the headlight switch...
 
67Dart273 said:
Wait a minute. Is this key on or key off? There is very very little in the car that can pulsate. Is it "even" or erratic?
Click to expand...
The key is off and out of the ignition switch; the DMM reading is erratic, jumping between .3 and .6A in no discernable pattern.
67Dart273 said:
Pull the 4 way flasher unit. Does it have a clock? And have you checked for aftermarket stuff like an old alarm, etc?
Click to expand...
I pulled both the emergency flasher and the turn signal flasher, no change. There's no clock or alarm.
67Dart273 said:
You need to disconnect the ign switch right at the switch, to find out if there is something wrong internally.

And find out if the switch had a "key in" light. There is a timer deal, small cylindrical device with 3 terminals. That would be a suspect.
Click to expand...
Now the car is just mocking me. Disconnected the ign switch, and the testing light just keeps blinking. I can hear it laughing at me as I'm stuck underneath the dash. There is a hole above the cylinder, but the car didn't come with the light.
 
Mattax said:
So do the door switches. The dome light is powered through a fuse. Removing the fuse didn't stop the mystery current.
Suppose its possible there is a weak short in the headlight switch...
Click to expand...
The headlight switch is about the last unfused circuit left that I haven't touched.
 
"The key is off and out of the ignition switch; the DMM reading is erratic, jumping between .3 and .6A in no discernable pattern."

You can not depend on that kind of thinking. There might be a fault somewhere in that circuit, and in fact, could actually be a cross--connect in the harness. THAT is a VERY common problem in all older cars with poor fuse protection. You get a short somewhere, either wrong (too large) fuse, or it didn't blow for some reason, or just part of the harness that is not fused, the wire heats up from a short and you have there, a heater (the wire) right inside the taped up harness. And next thing ya know, 2 or 3 OTHER wires have been heated up, the plastic insulation burned/ melted off, and one thing is cross connected to another.

ANOTHER thing you might try is look at your meter, go under an wiggle part of the harness. If it's still there, wiggle something else. Pay attention to "where" you are wiggling so you can go back over it again.

When you find it, LOL, you will be amazed.

Also disconnect sections of harness. Part of the engine bay--your bulkhead connector is in 3 sections. If you want to isolate the ammeter circuit, "rig" a wire separately when the ammeter section is unplugged, to feed power back in to it. Either the big black or the big red at the bulkhead.

Disconnect the tail harness in the left kickpanel.
 
Another thing you can do, and KD Tool and other outfits sell various tools of this sort. Your draw is enough that it should deflect a compass held very near the part of the harness that is being affected. Be aware, you might of course be so, that metal in the car with NO current will deflect the compass. But if you connect/ disconnect the battery and the compass deflects on part of the harness, then you likely have found part of the harness that contains whatever is drawing the leakage current.
 
yeah depending on the type of alternator a faulty diode can create a current flow, although it depends on the type of alternator. its usually the internally regulated type with loads of diodes.

if its a short somewhere and you are seeing pulsing that would imply current flow heats something which causes it to move and cut off the current flow. then cool again only to repeat... for that to just happen due to natural degradation of a wire or connector would be bizarre as devices that actually depend on this kind of action are usually very precisely made. i.e fridge or aircon control circuits from the 1950s and 1960s, by the time our cars were made it was resistor networks made up from coils that balanced a voltage to do the switching usually with a couple of transistors involved same kind of bridge and latching circuit
 
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Well, I'm not much of an electrical diagnoser anyway, but at this point I think I would just pull the under dash harness and visually inspect it for any burnt/melted wires - like #12 above. There's too much you really can't see while it's in the car.
 
Might be good to "back away" for a minute.

Don't eliminate stuff by "logic" because something could have a problem and be part of the problem. Loose contacts walking around in the ignition/ wiper/ headlight switches.

If you can see it on a sensitive lamp, that might be better than a meter, because you can "watch" it out of the corner of your eye.

So just to repeat:

1...Pull all fuses. If the load is still there, move on
2... Think and LOOK for hacks, like alarm circuits or aftermarket audio gear
3...Disconnect all you can to strip away, simplify the problem. As I said, EG separate the tail harness.
Pull out the headlight switch. And for SURE pull the ign switch.
4....Get the diagram and see what all comes off the ammeter circuit. Not all that much, internally. It feeds the fuse panel hot buss. Go get the fuse panel LOOK at the hot buss, and make damn sure nothing has been spliced in there

Ammeter circuit (welded splice) also feeds the alternator, which should now be disconnected and the black taped off, some years feeds the wiper switch (park circuit is live!!!) feeds the headlight switch which should now be disconnected.

We are running out of options.

As I said, separate the bulkhead connector. Does it go away?

Then if so, jumper power from the battery into the big red terminal of the bulkhead. With everything (above) you have disconnected, there cannot be much in there. I don't know how the ammeter could leak to ground, but you never know.
 
^^Sounds lgood^^^

Maybe along the same line of thinking. Disconnect everything. Then start reconnecting, first at the starter relay juntion, then the firewall, etc.
 
I was busy yesterday during the day and in the evening went with my boys to see the opening of Jurassic World - Rebirth (it was entertaining, but it was also as cheesy and formulaic as we had expected).
Back at it today; the headlight circuit was about the only one left to check. And of course, that was it. The Dart has @crackedback's headlight relay kit installed, but that was irrelevant to the issue, just another testing point in the circuit.
Pulled the switch and visually nothing looked out of the ordinary. Between the terminals was filled with 50+ years of detritus. The terminals themselves looked to be almost brand new. Cleaned out all the debris, coated the terminals in dielectric grease and plugged it back into the harness (still hanging below the dash, with a jumper wire grounding the switch frame to the door switch). No more drain. Pull out the lever and the amp draw jumps to 9 amps; push it back in and goes to 0. Fixed.
After reconnecting everything else, its back to diagnosing my stuck horn.
Thank you everyone for your help.
I didn't think to snap a pic until after I had started cleaning the switch. Between the terminals looks pretty clean, but you'll notice the brown film in the bottom of well, underneath the rheostat. That's dirt and debris that was also on top.
20250703_120956.jpg

After cleaning.
20250703_121933.jpg
 
Like I said, LOLOL, "when you find it, you will be amazed."

Tuck that away, tho, some of that moisture/ chemical, etc, could have gotten down inside.
 
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Decades ago, had a land line, and the previous home owner had strung wire for a couple of extensions. The phone got noisy and would sometimes not ring, except just buzz/ vibrate a little bit. That was years before I had a "megger" (high voltage leak tester) and I had finally stripped the wiring down to just a piece coming in through the wall from the exterior box, and 1 phone.

Anyhow, LOLOL one morning I was sittin on the throne, and looked down at the baseboard, near the corner of the shower. The phone line was tucked in the top of it, unused, and I thought, "I wonder?" It was only a couple feet long, ran down through the floor and spliced in the basement. Cut it loose, and YUP!!! It had gotten wet/ dirty/ etc

The phone "talk" voltage is low enough that it would usually work, but the ringer voltage would "bust through" and drop drastically
 
RRR with the subtlety LMAO

Glad you found it. Post 3 & 5 hit it on the head. After being around these things for 50 years... things that have caused issues like this are sometimes easy to find. Unplug that light switch connector, drain gone, you know where the issue is. Hit the easy button first, unplug stuff.

I just paid a bunch of money for someone to fix a house AC unit. I thought the main coil busted (had broken before and got bandaid fixed) because there was oil on the condenser structure. Never bothered to see if it was fresh. Yep bad diagnosis on my part. It was the MFing capacitor AGAIN... $30 part turns into a big bill because I didn't do the easy stuff first. OOF!
 

Oh, man. You are lucky you got an honest AC outfit. Many in the "big city" and even around here would have just gone ahead and replaced the coil!!!
 
id expect everything to work better... every connector and fuse has been removed and refitted if all of it was suffering from similar symptoms i think you fixed and bunch of stuff that had not happened yet :)
 
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