Battery ground to block
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Cross-Country
Joined: Aug 2021
Posts: 91
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Battery ground to block
Hey guys. I keep having issues with my main ground from the battery to the block. Thinking something wasn’t right I realized the bolt in there looked pretty new and it’s a 14mm. I thought it was a 9/16 but noticed the socket was a bit loose. I’m wondering if the threads are wrong too and that’s causing me some grounding issues. Any idea what size bolt is supposed to be in there? 78 f150 with a 400
Hotshot
Joined: Feb 2004
Posts: 10,808
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From: The Shenandoah Valley
Pretty standard, 1/4" bolts use 7/16" wrenches, 5/16" bolts use 1/2" wrenches then, 3/8" bolts use 9/16" wrenches, 7/16" bolts use 5/8" wrenches.
14mm is 8.818 sixteenths", or nearly 9/16". Is that the wrench size? I'm not sure what a 10mm bolt uses for a wrench, but it sounds close. In any case, was not originally a metric bolt on a dent side engine so someone just boogered it in there because it was close. 10mm figures out at 0.393" or a bit over 3/8" so they maybe screwed the threads up. If you pull it out, if a soft bolt, maybe block thread is OK?
14mm is 8.818 sixteenths", or nearly 9/16". Is that the wrench size? I'm not sure what a 10mm bolt uses for a wrench, but it sounds close. In any case, was not originally a metric bolt on a dent side engine so someone just boogered it in there because it was close. 10mm figures out at 0.393" or a bit over 3/8" so they maybe screwed the threads up. If you pull it out, if a soft bolt, maybe block thread is OK?
FTE Legend
Joined: Nov 2015
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From: Angier, NC
Being you are messing with grounds if you don't have one add motor to frame & motor to cab or frame to cab.
remember the motor / trans & cab sit on rubber mounts so no ground from motor to the other parts.
Dave ----
remember the motor / trans & cab sit on rubber mounts so no ground from motor to the other parts.
Dave ----
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Cross-Country
Joined: Aug 2021
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I appreciate the notes here. 77/79 so the ground doesn’t have to remain going to the block or is that a ground to block and and another ground as shown? When placing the extra grounds should I just buy new battery ground cables and use those? I know some of these questions sound dumb.
Moderator & parts slinger
Joined: Feb 2007
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From: S/W Missouri, Polk county
I would address the original ground to block hardware issue and go with the set up from factory. And then add the set up in the pic as an added ground.
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Fleet Mechanic
Joined: Sep 2014
Posts: 1,626
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From: NE Texas
The bolt HEAD does not matter, it is a question of the bolt THREAD. And yes, some metric threads are close enough to interchange poorly with standard threads. The main issue is whether the ground is clean and tight. Fix THAT first.
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Laughing Gas
Joined: May 2021
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From: Anderson, California
Check the depth of the hole, and length of your bolt.
Make sure your bolt is not bottoming out in the hole which may result in a loose cable-to-block fit, which would create a P*ss poor connection.
Make sure your bolt is not bottoming out in the hole which may result in a loose cable-to-block fit, which would create a P*ss poor connection.
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Cross-Country
Joined: Aug 2021
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Update. In case someone ever needs to know. 1978 f150 xlt ground to 400ci block bolt size is 3/8-16. It’s threaded all the way through. Can’t bottom out. Not sure what that metric bolt was but it was very close. I chased a tap through the threads and cleaned it all up really good. Threw a lock washer on there for good measure and it’s nice and tight.
Still have ground issues. Truck had no power once done. Back under the hood and checked all the connections on the solenoid and the cab lights popped on. Truck fired right up. Must have a ground issue on the solenoid. Used a test light and between the hot battery and mounting bracket of the solenoid I get a light. Same for where it mounts to under the hood. Wondering if one of my connections on the solenoid is iffy. Next time I’ll watch the dome light and mess with each wire individually until I get power. Maybe that will give me a lead on the issue.
Still have ground issues. Truck had no power once done. Back under the hood and checked all the connections on the solenoid and the cab lights popped on. Truck fired right up. Must have a ground issue on the solenoid. Used a test light and between the hot battery and mounting bracket of the solenoid I get a light. Same for where it mounts to under the hood. Wondering if one of my connections on the solenoid is iffy. Next time I’ll watch the dome light and mess with each wire individually until I get power. Maybe that will give me a lead on the issue.
Lead Driver
Joined: Nov 2006
Posts: 5,217
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From: Pa.
Update. In case someone ever needs to know. 1978 f150 xlt ground to 400ci block bolt size is 3/8-16. It’s threaded all the way through. Can’t bottom out. Not sure what that metric bolt was but it was very close. I chased a tap through the threads and cleaned it all up really good. Threw a lock washer on there for good measure and it’s nice and tight.
Still have ground issues. Truck had no power once done. Back under the hood and checked all the connections on the solenoid and the cab lights popped on. Truck fired right up. Must have a ground issue on the solenoid. Used a test light and between the hot battery and mounting bracket of the solenoid I get a light. Same for where it mounts to under the hood. Wondering if one of my connections on the solenoid is iffy. Next time I’ll watch the dome light and mess with each wire individually until I get power. Maybe that will give me a lead on the issue.
Still have ground issues. Truck had no power once done. Back under the hood and checked all the connections on the solenoid and the cab lights popped on. Truck fired right up. Must have a ground issue on the solenoid. Used a test light and between the hot battery and mounting bracket of the solenoid I get a light. Same for where it mounts to under the hood. Wondering if one of my connections on the solenoid is iffy. Next time I’ll watch the dome light and mess with each wire individually until I get power. Maybe that will give me a lead on the issue.
Tuned
Joined: Sep 2019
Posts: 381
Likes: 194
From: Port Charlotte, Florida
To build on what @redroad stated: I had this problem with an old Mustang. The screw holes in the inner fender where the solenoid AND voltage regulator mounted were hogged out and the self-threading screws would not get a good bite. My simple solution was to drill out the holes and use 1/4"-20 bolts, washers, lockwashers, and nuts. The lockwashers (under the nuts) bit into the metal and provided a good ground connection. Never had that problem again.
I can't over-emphasize how important it is to have good ground connections for every electrical circuit in your vehicle. It's amazing how much effect "just a little" rust or corrosion can have on circuit performance, especially if it's a high current circuit. Ohm's Law states that voltage = current * resistance. If the resistance goes up, the voltage goes down!
I can't over-emphasize how important it is to have good ground connections for every electrical circuit in your vehicle. It's amazing how much effect "just a little" rust or corrosion can have on circuit performance, especially if it's a high current circuit. Ohm's Law states that voltage = current * resistance. If the resistance goes up, the voltage goes down!
Fleet Mechanic
Joined: Nov 2009
Posts: 1,398
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I can't over-emphasize how important it is to have good ground connections for every electrical circuit in your vehicle. It's amazing how much effect "just a little" rust or corrosion can have on circuit performance, especially if it's a high current circuit. Ohm's Law states that voltage = current * resistance. If the resistance goes up, the voltage goes down!
When I put a new harness into the truck, I also added ground bars like these at the four corners of the truck where the lights are located. I then ran a 10ga wire to each of these locations. Ground wires from the light went to these bars also. Lights are always bright.https://www.homedepot.com/s/ground%2520bar?NCNI-5
Thread Starter
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Cross-Country
Joined: Aug 2021
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Thanks for all the help everyone. Ended up not being a ground issue at all. This wire I’m holding from the solenoid was broken. That blue connector was loose. Took it apart and replaced and now I have power again. However, I do think I’m going to take some advice here and add a few more grounds. Thanks!