Direct Short when attaching battery ?
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5th Wheeling
Joined: Jul 2016
Posts: 27
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Direct Short when attaching battery ?
Have been working on a 1969 f250 that had some issues with the ignition / idling when I purchased it as a parts truck form my '68 f100. While I did intend to use it for a parts truck, it is really too nice to salvage all the needed parts so figured I would try and get it running. It was running (other than being cold blooded at start up) and then it has sat for a few months since last start up. I picked up a new battery as the one that came with the truck just wasn't charging any longer. When the new battery was installed, the battery cables started arching as soon as I try and connect to the terminals. My only quick thought would be either the starter is stuck (although when touching the power cable to battery it doesn't appear to be trying to spin the starter) or possibly an issue with a short in the starter relay?
Any additional thoughts or theories would be greatly appreciated.
Any additional thoughts or theories would be greatly appreciated.
Fleet Mechanic
Joined: Aug 2007
Posts: 1,828
Likes: 253
From: Piney Woods of East Texas
Connect a volt meter in series with the battery and start unplugging things, pulling fuses till you see the volts drop to "0" zero. Then you have isolated the circuit pulling all the current. I would start with the Alternator.
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5th Wheeling
Joined: Jul 2016
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blue68f100, thanks for the reply. I'll try unhooking either the starter and alternator and see if the battery sparks when hooking it back up.
I also have a 68 f100 sb that was wrecked that I picked up recently that I was planning on using the f250 for as parts, but I think I've been able to get enough parts gathered that possibly I can keep the 69 f250 as a whole running truck.
I also have a 68 f100 sb that was wrecked that I picked up recently that I was planning on using the f250 for as parts, but I think I've been able to get enough parts gathered that possibly I can keep the 69 f250 as a whole running truck.
Lead Driver
Joined: Jul 2017
Posts: 9,600
Likes: 1,174
From: San Jose, CA
When you say they started arcing, do you mean there’s a little spark jumping between the two points? Or when you try to connect them does something really snap crackle and pop?
And if so, is there any smoke coming out of somewhere?
An arc could just mean something is on. Something as simple as a dome light.
A direct short would smoke some wires.
As stated, a heavy arc, but without something melting, could easily be the alternator going bad inside.
It’s a half short in effect. Not enough to melt a wire, but enough to cause the spark between the terminals and the alternator would become warm after a few minutes.
And if left connected, the battery would drain in short order.
And if so, is there any smoke coming out of somewhere?
An arc could just mean something is on. Something as simple as a dome light.
A direct short would smoke some wires.
As stated, a heavy arc, but without something melting, could easily be the alternator going bad inside.
It’s a half short in effect. Not enough to melt a wire, but enough to cause the spark between the terminals and the alternator would become warm after a few minutes.
And if left connected, the battery would drain in short order.
Lead Driver
Joined: Jul 2017
Posts: 9,600
Likes: 1,174
From: San Jose, CA
Before trying to connect the battery again though, go around the truck and look for things that might be on.
Is the ignition switch off?
Is the dome light connected? If so, close the door. Disconnect the regulator and Alternator and see if it still does it.
If you connect the battery temporarily, do the tail lights or headlights come on?
These are all things that could be checked.
Is the ignition switch off?
Is the dome light connected? If so, close the door. Disconnect the regulator and Alternator and see if it still does it.
If you connect the battery temporarily, do the tail lights or headlights come on?
These are all things that could be checked.
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5th Wheeling
Joined: Jul 2016
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1TonBasecamp, thanks for adding to the thread. I did go around and make sure everything was off (lights, ignition, doors closed) but still same effect.
The arcing coming off between the terminals and cables are (at least to me) way more than would be expected unless there is a strong direct short someplace.
Hoping to get some time this week to disconnect the alternator and starter (one at a time) to see if the same issue remains or not. I did pick up a new starter solenoid but wanted to see if I could narrow it down a little more before throwing new parts at it...
The arcing coming off between the terminals and cables are (at least to me) way more than would be expected unless there is a strong direct short someplace.
Hoping to get some time this week to disconnect the alternator and starter (one at a time) to see if the same issue remains or not. I did pick up a new starter solenoid but wanted to see if I could narrow it down a little more before throwing new parts at it...
Lead Driver
Joined: Jul 2017
Posts: 9,600
Likes: 1,174
From: San Jose, CA
Sounds good. But whatever you do, if it turns out that the old starter relay/solenoid was still good, don’t you dare throw it away!
That’s because the old ones are typically far better than the new ones. If the new one works, keep the old one as a spare
If the old one was bad, then good on your diagnosis being correct. And then make sure to mark it bad and toss it out!
That’s because the old ones are typically far better than the new ones. If the new one works, keep the old one as a spare
If the old one was bad, then good on your diagnosis being correct. And then make sure to mark it bad and toss it out!
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Cargo Master
Joined: Feb 2006
Posts: 3,009
Likes: 250
From: North Pole, Alaska
Here is my take on Ford batteries, starters, and starter relays.
1. Always take off the negative cable first, and replace it last. That way you are at the same potential if you touch the body somehow.
2. Always have it in park, or neutral if a manual. The reason for this is, you can have a bad starter relay, and the engine will crank over and start up even with no key in the ignition.I was cleaning the terminals on my dad's 77 F-150, and was replacing the cables back on when it started. Luckily it was in reverse when it did it, and I jumped in and pushed in the clutch, shifted into neutral. The second time it happened, I was working on my wife's 74 AMC Gremlin which had a Ford starter and relay (a bucket of everybody's spare parts). It started also, but I had it in neutral.
1. Always take off the negative cable first, and replace it last. That way you are at the same potential if you touch the body somehow.
2. Always have it in park, or neutral if a manual. The reason for this is, you can have a bad starter relay, and the engine will crank over and start up even with no key in the ignition.I was cleaning the terminals on my dad's 77 F-150, and was replacing the cables back on when it started. Luckily it was in reverse when it did it, and I jumped in and pushed in the clutch, shifted into neutral. The second time it happened, I was working on my wife's 74 AMC Gremlin which had a Ford starter and relay (a bucket of everybody's spare parts). It started also, but I had it in neutral.
Last edited by RichS2659; Dec 16, 2025 at 10:33 AM.
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