parasitic draw
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5th Wheeling
Joined: Jul 2020
Posts: 30
Likes: 2
parasitic draw
I'm in the restoration of 1976 F100 2wd 4.9 custom ,4 speed, no radio , no AC , manual steering , and brakes. Have been working on the head lights and signal lights. Replaced the 1157 bulb sockets in the front , and ran a new ground from battery to chassis. Lights and flashers are working. Went in the house for a few hours and returned realizing that I had left the key in run position and the battery was nearly dead. I charged the battery to 13.25 volts , unhooked the neg. cable , put a test light on the neg. cable and neg. battery terminal. With the key in the run position , the test light comes on. Started unhooking and unplugging the following components one at a time : Alternator , electric choke, fan motor , windshield washer, horn relay,, starter, headlight plug between switch and lights , ignition module , brake fluid switch, voltage regulator was sounding like a relay closing until unplugged. Removed every fuse one at a time . tail lights are unplugged and fuel sending unit is unplugged as well. Seat belt switch is unhooked .Test light burns bright with key in run position only . This is as simple a system as it gets , What could I be missing here ????????????????????????????????
Laughing Gas
Joined: May 2011
Posts: 855
Likes: 40
From: SoCal
I'm confused, shouldn't the bulb light in the run position? The battery is supplying voltage to the coil and ignition in the run position.
Okay I reread, and I think you're just measuring battery voltage to ground. Same as if you connect your test light across the batt.
Okay I reread, and I think you're just measuring battery voltage to ground. Same as if you connect your test light across the batt.
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5th Wheeling
Joined: Jul 2020
Posts: 30
Likes: 2
Thanks for the reply , So what I'm seeing with the test light is the voltage going to the coil ( ignition module is unplugged). So leaving the key in run position would normally drain the battery by sending voltage to the coil . You're saying that there is no parasitic draw that leaving the key on would drain the battery normally.
If that is so , then as usual "I" have jumped to a hasty conclusion .
If that is so , then as usual "I" have jumped to a hasty conclusion .
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5th Wheeling
Joined: Jul 2020
Posts: 30
Likes: 2
Thanks for the conformation friend ! I pretty much spent all day checking fuses and components , but will try to feel like time was not totally wasted as I know everything works , and I got to clean terminals smear electrical grease on everything I took apart. Thanks to those who responded and their kindness at not rubbing my face in it.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Depending on the ignition type, leaving the key in "run" (without the engine running) for a good while may roast certain components. Ignition coils for example don't care for this, ignition modules, contact points, etc. In other words "Don't do that!!".
Interestingly enough maybe I'm reading what you wrote the wrong way, but a dead battery won't be charged at 13.25 volts indicated on the charger, not even close believe it or not. They approach a full charge at around 14.5 volts or better, and then need to cook for a while after that to fully saturate. Maybe that's not what you meant, maybe you know this already. Just thought I'd throw that out there.
Interestingly enough maybe I'm reading what you wrote the wrong way, but a dead battery won't be charged at 13.25 volts indicated on the charger, not even close believe it or not. They approach a full charge at around 14.5 volts or better, and then need to cook for a while after that to fully saturate. Maybe that's not what you meant, maybe you know this already. Just thought I'd throw that out there.
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