Parasitic Power Draw on my 62 Comet

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1962Comet
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Parasitic Power Draw on my 62 Comet

Post by 1962Comet »

For the last few years I have been chasing a parasitic current draw issue. I couldn’t keep my battery from discharging over the course of a week or two. I knew with these older cars, there’s the potential for pinched wires, aging components and that just about anything was possible. I had a constant 80 mA (0.08A) being drawn when “everything” was off. I could keep it charged with a battery tender but that was a hassle and shouldn’t be necessary.

Now, I’m an electrical engineer and should have the “smarts” to figure this out, but after a cursory review of everything a few years ago, I quickly “remedied” the problem by installing a battery quick disconnect switch. So that was that and I put it off for a while. Now I don’t drive the car much so it was not an issue to lift the hood and turn the knob on the disconnect switch and be on my way. But, with all the flippin' rain we’ve been getting this summer, I decided to spend a Saturday in the garage and hunt this thing down. The wife was working so I would not be bothered by other chores that needed attending.

Since this was serious mission that I was on, I got out my best DMM, my Fluke 73, and not one of the Harbor Freight freebie meters that I had lying around. I disconnected the battery, put the meter inline and I was on my way. I started disconnecting harnesses one at a time keeping one eye on the meter. I turned the battery disconnect switch off in between wire disconnects so I wouldn’t short any wires. I disconnected wires to the Generator and Voltage Regulator as well. I had rebuilt the generator myself a few years back and thought that maybe I had a flying wire strand inside. But nothing so far pointed to the culprit.

With just about everything disconnect from under the hood except the main connection at the starter relay, I disconnected the harness heading through the firewall into the passenger compartment. Poof, I was suddenly reading 0.00 A dc on the meter. Finally, I had a direction I could head. Now, I’ve had some back issues and lying down under the dash is not my favorite position, so I was not thrilled with what I knew was coming next.

I grabbed a few tools, my flashlight and some ty-wraps. I knew I’d be cutting a few ty-wraps since I had all the wiring neatly tucked up out of sight. I kicked off my shoes and lowered myself onto the driver side floor with my butt up on the seat. As I disconnected each wire, I had to climb out to look at the meter out near the battery. Lying on my bad back was not an issue, it was getting back up without twisting, that was. Twist the wrong way and I’d get a zinger (as I call them) up and down my right side. That hump is no help and there’s nothing much to grab on to, to pull yourself up.

Finally, I pulled a rather new looking red wire from one of the 3-position connectors and bam, it was gone. Now, my car is mostly original, except for (wait for it) a Sunpro Tach. I had mounted it to the steering column when I first got the car. It was supposed to be temporary, while I tuned the carburetor that I had rebuilt. But, I left it in place as it was out of the way and didn’t look too out of place. So yes, I had connected the tach’s power wire to a connector that was always on. What was I thinking back then? I had correctly connected the wire for the tach’s light to one that only went on when the lights were on but somehow messed up the main power. Maybe I didn’t think a tachometer needed power when it wasn’t “tach-ing”. I found the installation instruction and sure enough they highlighted that fact that you want a switched power source. Doh! So I moved the power connection to the threaded stud at the back of the ignition switch and cracked open a beer.

Here I was thinking that some old worn out part was the problem when it turned out to be the newest part in the whole car. Actually it was the newest owner that was at fault, if anything.

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1962 Comet - 2-Door, 170 cu.in. with 6,950 Original Miles.
https://www.dplivingston.com/picking-up ... -62-comet/ <-- follow my 1962 Comet Restoration.

lavron
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Re: Parasitic Power Draw on my 62 Comet

Post by lavron »

Sometimes it is nice to find them that quickly :D

Glad to hear you got it solved.

See Ya,
Mike
Mike's build thread
viewtopic.php?f=9&t=13058
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1962Comet
Posts: 95
Joined: Mon Nov 28, 2011 12:34 pm
Location: Rochester, NY
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Re: Parasitic Power Draw on my 62 Comet

Post by 1962Comet »

Thanks Mike,

I guess I procrastinated a little over this one. With a little forethought I guess I could have solved this without even lifting my meter.

Dan
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1962 Comet - 2-Door, 170 cu.in. with 6,950 Original Miles.
https://www.dplivingston.com/picking-up ... -62-comet/ <-- follow my 1962 Comet Restoration.

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