I recently purchased a 1951 Ford F1 with a V8 Flathead that is still wired for 6 volts. Being that it is a “positive ground” do I connect the ground cable that is directly under the distributor to the (-) terminal or to the (+) terminal on the battery? When I purchased a new 6 volt battery, I connected it up like most cars and trucks on the road today, but when I turned the engine over the bolt that holds the (-) cable to the block of the engine became extremely hot to a point that the bolt turned bright red. When I flipped the battery and connected the (+) to the cable connected to the block (near distributor) the heat that was causing the bolt to turn very hot went away. The engine still turned over by pushing the “push button “ on the dash to the left of the steering wheel. Any help would welcome.

 

Welcome Sonic!

Your truck was originally 6 volt positive ground. Best to use a wiring diagram to guide any work. Take a look at the attached link to avoid terminology differences. And we really like pictures.

https://www.ford-trucks.com/forums/1...951-f-1-a.html

 

Here are four pictures. The first picture shows the starter relay which is currently connected to the (-) side of the battery terminal. You have the wire starter wire connected to the left. The green wire in the middle goes to the “push button” on the dash and to the right is the the battery connection, which includes two red wires going to the voltage regulator. There was also another red wire that was connected to the terminal connection that went directly to the ignition switch. I cut that wire and moved it to the (+) cable terminal to see if that would make a difference and it did not.

The second picture shows the battery layout with the red wire from the ignition switch being moved from (-) to the (+) side of the battery.

The third picture is of the coil showing the positive and negative side connections.

The four picture show the battery and how I currently have it connected. The (+) cable is running the the side of the block were the negative is connecting to the starter relay.

Does this look correct?

Thanks

 

By my take, the positive post is connected to the starter solenoid. It should be attached to the block or frame ground. The negative battery post attaches to the solenoid. Use the wiring diagram as a guide and don't reinterpret the design. Confirm that all the connections follow the diagram under the hood and to the starter button. That should get you back on track.

So the first picture isn't the current setup? Just a bit confused here.

 

I have reviewed the wiring diagram in the past and again a couple of nights ago (I saw it out on the internet). So that I understand, you want me to flip the battery back around and connect the cable coming from the side of the block (near or under distributor) back to the neg. (-) side of the battery. Then take the cable that is connected to the starter relay (solenoid) and connect it to the pos.(+) side of the battery. When I first purchased the new battery I had it connect this way. When engaging the "Push Button" the cable that was connected to the side of the block and connected to the neg. (-) side of the battery became very hot. The bolt that holds the cable to the side of the block turned bright red as if someone had placed a torch to it. Basically it did not like that at all. Not sure what or why that is happening.
Thanks again,
Bill

 

+ POS battery terminal, cable to engine/frame (ground)

 

Hey Bill,
Your battery cables should be connected like this:
Your negative post should connect to the right hand terminal of your starter relay (or solenoid) which has the red wires that connect to you ignition switch and your voltage regulator Battery terminal.
Your positive battery terminal connects to the cable that runs to ground on the engine block. Hence the term "positive ground".
I am not sure where that red wire runs that you attached to the pig tail on your positive ground battery cable, but I would cut that off and reattach it back to where it connected before you made the change.
When those are correct, we can troubleshoot more from there if needed.
I can't quite tell from your pictures but make sure your battery cables are heavy 0, 1/0, or even 2/0 AWG.

 

Its best to not over think the difference between positive ground and negative ground - when wiring, pretend that black cable coming from the negative post is red and hook it up as you would. A 6volt positive ground coil that has a + symbol means the positive is to ground, just as a 6volt dizzy ground wire is positive to ground. Be sure you are not using a 12 volt coil. Also, I'd like to see a much bigger sized Positive to ground cable coming off the battery - mine is red in color 4/0 AWG in size - a huge cable to ground and also have several grounding straps from frame to block, block to firewall, frame to fuel sender, etc.

 

Thanks. I replaced the cable from the pos.(+) side of the battery to the block this afternoon. It was a 2 gauge cable and I replaced it with a 1 gauge per the advise of another Ford professional 🔧. I had to order the other 12” cable that goes from the starter relay (solenoid) to the neg.(-) side of the battery.

There is a red wire that’s connected to the neg.(-) side of the battery that runs all the way back to the ignition switch. You can see it in some of pictures. Does this connection sound correct? I keep moving this wire between negative and positive to see if will make any difference. Nothing new happens. On the back of the ignition switch there are 3 connections. One is the “blue” wire that goes directly to the coil (pos. [+] side). The second wire “red” goes directly to the neg.(-) side of the battery. The third wire(s) (x2) go directly to the gauges. Nothing else is connected to the back of the ignition switch.

Thanks,
Bill

 

I want to reiterate that you need large cables. I went to a big truck shop and had them make me ones to length out of 2/0 cable.
Here is the difference between 12V versus my new 6V cables


Here is part of a wiring diagram for my 55 6V the parts you are talking should be the same. The red wire off the solenoid goes to the starter button.
Notice the negative post on the battery goes to the solenoid and the positive post is grounded to the frame.

 

I purchased a wiring diagram from here: https://classiccarwiring.com/product...wiring-diagram
That link is for your 51. It comes in an 11X17 laminated sheet. Very handy. I then scanned it to my PC so I have a PDF of it as well. It's only $18 and worth it if you ever need to do any wiring work.

 

Bill, I think your truck has been rewired at some point. If I recall correctly you should have two yellow wires run from the battery side of the solenoid. One, a heavy yellow wire runs from the solenoid back under your dash to a buss bar that is connected to a pair of circuit breakers, its that yellow that provides -6 volt current to another yellow wire that feeds your IGN switch. The other yellow on the solenoid provides power to the horn which sounds if the horns return is grounded thru the horn button. This is if I recall all of this correctly. So you have red wires, so your harness must of been replaced at one time. The only question is, did they wire it like factory?
About the red wire you are switching back and forth. It probably feeds again to the negative side of your battery. So reconnect it that way. If you are connecting it to postive ground, you could be creating a short circuit is something else is not wired correctly and your IGN switch gets turned on
Like others have said get a wiring diagram. And if you don't have one already, buy and learn to use a multimeter. It will really help you in the long run!

 

This is a very good point and one that I was going to mention as well. In the 50s, the hot wire was not RED - it was YELLOW. Be clear in your mind that negative is HOT! Positive is ground.

Hope this diagram helps - its shows the circuit breaker that is under under your dash near the instrument panel.. The second photo is of my 54 6volt positive ground "junction block" - the large yellow vertical wire is the hot wire from the negative side of the battery/solenoid and provides hot (same size yellow wired running horizontally) to the circuit breaker then the rest of the truck. The Red/Blue wire (small wire on top) connects to the starter button and the solenoid.

 

The wiring diagram has been ordered. I ordered the larger size as eye sight is not so good these days. Thanks for the information.

Very helpful,
Bill

 

Sonic Bill: If you haven't already done it, please put your red felt anti-corrosion washer on the (+) terminal of your battery and the green one on the (-) terminal. It will help eliminate confusion in the future. Your new NAPA battery looks like a Group 1. I've always run a Group 2 in mine since they normally have a bit more capacity. I have mine wired as Negative Ground, but only because my wife bought me an aftermarket radio that would have been difficult to hook up otherwise. - Bob