Chasing a parasitic drain on the ammeter circuit

[RBConvert]

About a month ago I reinstalled the magnum engine into Dart after a complete rebuild. I mention the build only in context because the issue at hand was present before the build ever started. But now that the car is running strong, it's time for me to tackle the minor annoying issues that I've been avoiding for some time.
There is a minor parasitic drain to the battery. Bridging the negative cable and post with my DMM set to Amps, it's reading .3 - .6 amps. I verified with the test light.
Following SOP, I removed each fuse one at a time to isolate the circuit, with no change. I then removed all the wires from the alternator batt stud, again no change. Hmm. The starter is brand new as part of the engine build, so I pulled the starter cable from the starter relay main stud. No change.
I then pulled the positive wire on the stud that goes into the bulkhead via the fusible link. Bingo! Light went out.

 

[RBConvert]

So I kept going. Pulled the fusible link out of the bulkhead connector and that was it, no more drain.
Here's the back story. Last year I noticed that the fusible link was burned; the insulation was burned back but the wires were still in place so I never lost power. But I don't know for how long the fusible link was blown. The ammeter constantly shows discharge, even though the alternator is putting out 13.6V at idle. I've verified the output at the alt batt stud and the positive post on the battery.
The car was an original /6 auto, and the PO swapped in the 5.9 magnum and tremec transmission. The wiring is almost all OEM; with additions to convert to the V8. It's now an electronic ignition with a PowerMaster alternator.
Under dash wiring is also all original. All the gauges work (with the ammeter working, but showing discharge). A Sun tach is the only added gauge.
So I guess my next move is to pull out the IP and check the wiring to the ammeter. I can understand a voltage drop, but I'm left wondering how the circuit can show an amp drain.
What should I be looking for, or testing to find the source?
Picture of the dash. Horn button is off because I'm also chasing a stuck horn. The horn isn't an issue because the switch wire at the wheel and the wiring to the horn relay have both been disconnected.

 

[crackedback]

Something in the cabin is likely drawing, radio/clock etc.

Pull fuses until you find it. It could be something that is hard wired as well, light switch...

 

[RBConvert]

Something in the cabin is likely drawing, radio/clock etc.

Pull fuses until you find it. I could be something that is hard wired as well, light switch...

First thing I did was pull each fuse, with no effect. The most obvious would be the aftermarket radio but not the case. The radio is wired to switched power.

 

[crackedback]

If the radio is electronic, it likely has a secondary power wire to maintain presets.

Disconnect the connector at light switch.

 

[RBConvert]

Something in the cabin is likely drawing, radio/clock etc.

So pulling the fusible link isn't really telling me anything because all I did was isolate the interior wiring from the batt. True?

 

[crackedback]

IMO, it narrows down the area the issue may reside.

Check the black and red charge line bulkheads too. If they are melted you could get crossover to other circuits int he housing.

 

[67Dart273]

If you have pulled all fuses, to no avail, then........

think hard about other circuits. Dome, courtesly, glove box, trunk lamp. Are they all out?

That is a substantial amount of current. If it is a partial short, it should be generating heat. .3A x 12V is 3.6watts, and .6A x 12V is 7.2 watts That is plenty enough that you could feel it if you feel along a harness

RE-connect your ammeter circuit as this tells you nothing. At least not really. Because you have disconnected a fair amount of circuitry in there.

FIRST thing I would try is to disconnect the alternator output cable. Leaky diodes, or a leaky radio suppression cap. Be CAREFUL as the alternator output is NOT fused except for the damn poor fuse link.

If you are running a non factory alternator, such as a "1 wire" or maybe a Delco with integrated VR, I would for sure suspect and disconnect that.

Next, do you have an aftermarket radio? Many of those have a full time 12V supply to keep the memories alive. If the radio itself works (wired such as) with the key off, it might be leaky components in the audio PA circuits.

Also look for other circuit modifications, added / hacked wiring. Maybe some old alarm system, etc.

IT WOULD BE RARE but there is some possibility that the contacts in the ignition switch have become dislodged and are remaining in poor contact when "off." With everything else off, and fuses out, and while monitoring the load on your meter, separate the key switch connector. See if it's warm, and try wiggling the key to see if the problem changes. Before doing this DISABLE THE start circuit. Disconnect the start solenoid wire at the relay, the "square" looking screw terminal.

Can you round up a thermometer gun? With the load "drawing," that is plenty of heat that it should show up as elevated temps near the short or load

And most important, WHAT IS IT THAT WE ARE WORKING ON? Year, make model

This is IMPORTANT as there has been changes over the years. A rig with column ignition may have the "key in" lamp circuit, which has a heater operated timer relay. The 74 cars had the dreaded seat belt iinterlock box

Go to MyMopar.com if you have not and download the proper service manual. You may have to sub Plymouth vs Dart as not all years are covered.

 

[67Dart273]

Ah, yes, clock. Not many are equipped, that is certainly another possibility, thanks Cracked.

 

[RBConvert]

If you have pulled all fuses, to no avail, then........

think hard about other circuits. Dome, courtesly, glove box, trunk lamp. Are they all out?

I had removed the dome light because I was constantly going in and out of the car. There is no trunk, glove box, or courtesy lights.

That is a substantial amount of current. If it is a partial short, it should be generating heat. .3A x 12V is 3.6watts, and .6A x 12V is 7.2 watts That is plenty enough that you could feel it if you feel along a harness

I will check the harnesses.

RE-connect your ammeter circuit as this tells you nothing. At least not really. Because you have disconnected a fair amount in there.

FIRST thing I would try is to disconnect the alternator output cable. Leaky diodes, or a leaky radio suppression cap

Alternator cables were the second thing I disconnected after the fuses.

Next, do you have an aftermarket radio? Many of those have a full time 12V supply to keep the memories alive. If the radio itself works with the key off, it might be leaky components in the audio PA circuits.

The radio will be my first stop.

Can you round up a thermometer gun? With the load "drawing," that is plenty of heat that it should show up as elevated temps near the short or load

Yes, I have one. Thanks.

 

[RBConvert]

Next, do you have an aftermarket radio? Many of those have a full time 12V supply to keep the memories alive. If the radio itself works (wired such as) with the key off, it might be leaky components in the audio PA circuits.

Radio is my first stop, its aftermarket with presets. But shouldn't a correctly functioning radio only draw 50mA max?

Also look for other circuit modifications, added / hacked wiring. Maybe some old alarm system, etc.

IT WOULD BE RARE but there is some possibility that the contacts in the ignition switch have become dislodged and are remaining in poor contact when "off." With everything else off, and fuses out, and while monitoring the load on your meter, separate the key switch connector. See if it's warm, and try wiggling the key to see if the problem changes. Before doing this DISABLE THE start circuit. Disconnect the start solenoid wire at the relay, the "square" looking screw terminal.

Can you round up a thermometer gun? With the load "drawing," that is plenty of heat that it should show up as elevated temps near the short or load

And most important, WHAT IS IT THAT WE ARE WORKING ON? Year, make model

This is a 68 Dart with mostly all original wiring. The PO had to convert the under hood harnesses from the original /6 to the V8. He also installed a Classic Air a/c system. Aside from the aftermarket radio and the a/c, the under dash wiring looks all original.

Go to MyMopar.com if you have not and download the proper service manual. You may have to sub Plymouth vs Dart as not all years are covered.

I have the FSM and an 11x17 laminated full color wiring diagram.

 

[65 Cuda 340]

The source of the slow drain in my 65 Barracuda. Ran OK, but would drain the battery if left sitting for a few days. Couldn't see it from underneath, only saw it after I pulled the harness.

 

[Inertia]

Debris in the cigar lighter.
Clock is an intermittent thing, momentary, - to wind a spring .

P.S. perhaps unplug the head lite switch if not mentioned. (Rheostat?)

 

[RBConvert]

The source of the slow drain in my 65 Barracuda. Ran OK, but would drain the battery if left sitting for a few days. Couldn't see it from underneath, only saw it after I pulled the harness.

View attachment 1716424705

Yeah, that looks nasty. I would think that if you pulled whatever fuse(s) connected to that harness, you would've found the draw.

 

[RBConvert]

Debris in the cigar lighter.
Clock is an intermittent thing, momentary, - to wind a spring .

P.S. perhaps unplug the head lite switch if not mentioned. (Rheostat?)

I'm going to have to start disconnecting connectors until I find it. It's not the brake light switch or the flashers. Working on removing the radio.

 

[67Dart273]

Debris in the cigar lighter.
Clock is an intermittent thing, momentary, - to wind a spring .

P.S. perhaps unplug the head lite switch if not mentioned. (Rheostat?)

I've seen a lighter once. Rare, but yes.

The clock, if the wind solenoid is jammed, the contacts could be stuck closed. But both those are fused, I believe

 

[67Dart273]

"Radio is my first stop, its aftermarket with presets. But shouldn't a correctly functioning radio only draw 50mA max?"

Things do go wrong. As I said, if the radio is not wired through the ign switch, leaky PA components for sure. I don't know what go go wrong in the "keep alive."

 

[Kern Dog]

I had a draw to the system in one of my cars. It was the radio in my case too. The constant power circuit.

 

[Mattax]

'68 Dart?
And you pulled every fuse?
Radio should be on the switched (accessory) buss. And I would think with presets its still 'off' with the presets stored internally with its own battery. But just in case, disconnect it.

A/C should have no power with key off, but again, disconnect it - it should be fused making that easy.

Dome, and trunk lights are on a fuse.

'68 had an optional key light. See if that is fused. probably was but I don't recall.
There's some other options that maybe could draw, and might not have been fused. I forget when headlight warning was offered. Suposed to let you know the headlights when opening the door or somehting like that.

Having gone through all that, seems to me the only items that are unfused with key off are brake lights, and horn. Plus the possibility that the diodes in the alternator are 'leaking'. Disconnect the battery negative, disconnect the alternator output wire at the alternator, reconnect the battery.

 

[RBConvert]

This Dart was a stripper model, no clock or accessories to speak of. The pulling of each fuse did not isolate the circuit. I started pulling the radio this afternoon but it got too hot in the garage (98° outside) so I packed it in until tomorrow.
I would also suspect the horn circuit, namely because the horns are stuck in continuous mode. But the switch wire at the wheel and the horn relay itself are both disconnected.

 

[65 Cuda 340]

Yeah, that looks nasty. I would think that if you pulled whatever fuse(s) connected to that harness, you would've found the draw.

Had a dead short inside the alternator which shut everything off with a rather large "POW.". Replaced the alternator, which seemed to fix the problem except it now had a slow drain somewhere. When I took the harness out, I discovered that the insulation had burned off the wire to the ammeter (and burned through the tape wrap). Ammeter still worked, as the wire itself was intact. Not sure where it was leaking off the bare wire, as I didn't bother to unwrap the harness. Just replaced it with NOS, which fixed the problem.

 

[Kendog 170]

I'm not great with electrical. You could unplug the ignition switch rather easy to test. Ameters fail. Maybe temp bypass? Just spit balling here.

 

[Mattax]

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.

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

So now its down to
a. the two fused circuits on the hot buss, which you've tested by removing the fuses.
The dome lights are fused, the brake lights and the hazard is fused, so its not them.

b. the alternator.

c. a faulty switch. As Kendog mentioned, could remove the connector from the ignition switch pretty easily.

d. Feed from the horn relay to the horn switch.

Any others I'm missing?

 

[RBConvert]

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

So now its down to
a. the two fused circuits on the hot buss, which you've tested by removing the fuses.
The dome lights are fused, the brake lights and the hazard is fused, so its not them.

b. the alternator.

After the fuse test, I removed all the wires from the batt stud, no change. I left the two field wires on, but I wouldn't think they could produce a draw.

c. a faulty switch. As Kendog mentioned, could remove the connector from the ignition switch pretty easily.

I haven't gotten to the ignition switch yet.

d. Feed from the horn relay to the horn switch.

The horn relay wires are all disconnected.

Any others I'm missing?

I'm still poking around the back of the radio. The main power is switched. The circuit has an inline 2A fuse that I'm going to disconnect as part of the elimination process.

 

[RBConvert]

I'm not great with electrical. You could unplug the ignition switch rather easy to test. Ammeters fail. Maybe temp bypass? Just spit balling here.

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.