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flat head: 6 volt or 12 volt

4K views 10 replies 4 participants last post by  Irelands child 
#1 ·
Hi guys. I just became the proud owner of a 1940 ford deluxe. A really great barn find. It still runs with a flathead v8. I dont have any markings or numbers off of the engine yet. How do I know whether the car is supposed to be fitted with a 6v or 12v battery? The previous owners ran the motor on 12v. It has an alternator fitted. Would it blow fuses if you run on 12v if it is a 6v system? Can i test things like the coil to find out?
 
#2 ·
alternator

The 1940 Ford was initially a 6 volt system. At some time your car was changed to 12 volt.
AFIK 6 volt cars did not use alternators.
Check the lighting. If the lighting and gauges work OK, stick with the 12 volt system.
You should be fine.

vicrod
 
#3 ·
Ok, i've established the following. Definitely running 12V. Lights have been converted to 12V. I still have one million questions.

It is fitted with a later model 8BA engine.

The alternator still runs through a voltage regualtor (dont know if its 12v or 6v) It also runs a wire through a relay to the instrument panel. I suspect it will be from the ignition to excite the alternator.

Here is the jackpot question. Is this suppose to be negative ground or positive ground. I connected the battery as a negative ground. The engine turned and started fine. The wipers work. I can hear the old horn relay click but no sound from the horns. Also dont know if these are still 12v or 6v horns and relay. Surely the engine would have turned in the wrong direction if if was connected incorrectly?

Fuel guage was not showing anything but there is not much in it.

I started opening the wiring harness. ALL THE WIRESS ARE RED!! Some of them are off.

Im starting to think I should rip it all out and start over and make sure everything is 12 volt.

Any Comments?
 
#5 ·
Well right there's your problem.....red wire's bad!........lol

Looks like a relay, but if you have turn signals, it might be a flasher can.

If you intend to keep this vehicle, I truly believe your beast course of action would be, as you already know, rip it out and start over. It all may work now but later on, it will be a maze of "which wire goes where". There are tons of re-wire kits avail and there are just as many opinions as to which one is better........... I tend to use the Painless kits, not the cheapest, but I am very satisfied with the quality and ease of installation. Just about every kit has labeled wires and fuse boxes etc........

My 1st re-wire took a couple to three weekends to install. Easy day really, don't do what I did and leave the old one in and remove it as I went, didn't work out well for me, ended up removing the whole thing. My suggestion is start removing the old one taking pictures of all connections and use masking tape to label where it physically came from. When you start to put the new one in, solidly mount the fuse box 1st and run the wires to where they will generally end up, then starting at the fuse box place the wires in the finial resting place, using wire ties for each side of a turn, corner, obstacle, tying and securing everything tightly in place. Then and only then make your final "proper length" cut.

I didn't and ended up with a mess, ended up undoing just about every connection and re-doing the length. Don't leave extra length in the harness wires for "later on" trouble shooting, again I did and it was a mess. If you want a wiring diagram, draw one before you put the thing in the car, again I didn't and in the end , I removed the entire harness from the car, made my diagram and when I re-installed it in the car, I did it correctly and everything went smooth, except for all the re-terminations and those pesky 4 inch wire section I had to cut off.....lol
 
#6 ·
That wiring looks like a disaster waiting to happen!!
I used an American Autowire 'kit' for my car. What I liked about that product is that every circuit had a separate diagram as well as an overall system drawing where I could add or delete circuits (I copied many and did changes on those pages first). Other kits like Painless and Kwik Wire have something similar or at least instructions. If you can or want to spend the time, you can also do your own wiring design, but I found that keeping wire colors to usual industry standards - and most kits are based on GM, it got really expensive to buy the correct color, gauge and type of insulation on the wire wire plus most of the needed connectors were supplied.

That horn - my bet is that the PO wired them directly rather then through a relay and what you are hearing are horns trying to work. The gauges not working - there may be a 12V to 6V resistor, but any modern alternator is negative ground where a '40 Ford originally was 6V POSITIVE ground and the original gas, temp and oil pressure gauges toasted.

Sounds like a good project to me.
 
#9 ·
What is this??

I found these two monsters under my dash while I tried to trace all the wiring.

On the left is the ballast resistor but I have no idea what the part on the right is.

There are two terminals each with 3 wires. I traced most of the wires and they look like this

Left terminal (Alternator/Starter Solenoid, Ignition, Nowhere)
Right Terminal (Light switch, into roof possibly dome light, into front light harness)

Is there a connection between these two terminals?

The first mentioned wire is obviously the supply from alternator and battery. If wire two goes to the ignition I would think this is the 12v supply to the ignition?

Right Terminal: The first wire goes to the light switch and I suspect this is the 12v supply to the light switch. If this is a supply then it would make sense if the second (into the roof) is a supply for dome light but not sure then what the 3rd would be for. If this is not a supply TO the switch but FROM the switch this could actually be the park lights but I could not confirm that one of the other 4 terminals of the light switch is then a 12v supply.

PS I also found something that looks like a 12v to 6v converter. Hopefully when I test it it still works and I dont need to replace any guages.
 
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