Disclaimer: I'm a muscle car guy, not an expert in vintage Fords (although I've successfully gotten a few old flatheads to run...). The vehicle in question is a 1951 Ford pickup, it belongs to an older fellow who's got me doing a bunch of TLC type things. On the list is a 12V conversion. The owner already installed a GM style 1 wire alternator using a kit he bought. I've got the 12v coil, lights, voltage drops for the gauges, etc...I have a pretty good handle on the job but one thing I'm unsure of is the factory circuit breakers. I've read ten or twelve articles on the conversion and only one mentions removing the breakers and building a fuse panel. Other than a set of dual exhausts and the alternator setup it's bone stock. Is there a need to replace the breakers with a fuse panel? The wiring in the truck is in excellent shape & there are no electrical accessories being added other than a universal turn signal setup. I'll use an inline fuse on that so there won't be an extra load on either existing breaker. I can build a small fuse block, but I'd rather not if I don't have to.
Circuit breakers are made to trigger at a certain amp range. Keep in mind, 12 volt systems run at 1/2 the amperage of 6 volt systems. If you understand me, the question is answered
Searching doesn't give an honest explanation on what the difference between the two is. There is somewhat of an explanation here https://www.google.com/search?q=6+v...uAfQFsIHBzItNS43LjHIB40B&sclient=gws-wiz-serp The gist of it being that A six volt system might need a higher amp rating circuit breaker than a 12 volt system would.
I believe a '51 Ford truck has one circuit breaker from the factory for the dash lights and it doesn't look like a regular circuit breaker. With the differences in power draw and wiring size, 6 volt circuit breakers would, in general, be twice the capacity needed, and therefore would not offer the protection desired, so I'd get rid of them (or it).
My Ford was rife with little fuse holders and some real sketchy wiring in general. Everything came out and I went with a harness with a modern fuse panel.
Thanks all, Rusty Valley - I think I get what you mean. Watts (power) = volts x amps. If you double the voltage you can half the amperage to generate the same power. As a result the existing breakers will have too high a limit to protect the circuit. Similar theory if you wired an ordinary electrical outlet in your house to a 30 amp breaker instead of a 15 amp. If it were my truck I'd do a new harness but it's not my truck.... Further to this project - I'd like to retain the existing ammeter. I've been going thru factory wiring diagrams; as I understand it electricity flows into the truck from the voltage regulator to the buss bar on the gauge pod. The other side of the buss is the battery charge wire that passes thru the loop on the ammeter, exits than cab, and attaches to the same terminal on the starter solenoid as the battery. I'm not sure the best way to do it with the one wire alternator?
That inductance type ammeter is the same as I have in my 53. I ran the wire just as you described and it works fine. leave enough slack in the wire so in case you ran the wire backwards thru the ammeter hoops, you can reverse it.
OK, if I'm reading this right all your doing is replacing various 6V bits with 12V bits. If the existing harness is original (or an exact replacement), the OEM circuit breakers will be fine. Remember, they are there to protect the wire, not the device. Yes, the load will be reduced, but changing or removing the breakers won't improve the overcurrent protection. You have the lights and gauges figured out, but your '12V' coil may not be right. There really isn't any such thing, it's all about what the primary coil resistance is. Typically, all 6V AND 12V coils have the same resistance, right around 1.5 ohm. In a 12V application, a ballast resistor is used to drop voltage to 6V. To be an actual 12V coil that resistance needs to be about 3 ohms, no ballast resistor. Be sure and check both coils for this, measuring across the two screw terminals. Nearly all '50s/60s 12V OEM point ignitions used a 1.5 ohm coil with a resistor, most with a ballast bypass circuit for better starting (more on this below). Your 6V coil will work fine, just put a ballast resistor in the power lead to it. Running a 1.5 ohm coil without the resistor full time will kill the coil and burn up the points. If you have a heater with a fan motor in it, it may or may not live long at 12V. If it's multi-speed, avoid running it at full speed, that will help with longevity. Last, the starter/solenoid. IIRC these are positive ground, you're switching to negative ground. Plus they use a pushbutton on the dash to engage the starter. The coil inside the solenoid won't like 12V, the solution is swapping to a '56-up Ford 12V solenoid that looks like this... The problem here is grounding is done through the mounting bracket, your pushbutton won't work. But add one relay and now it does, plus you can add the ballast bypass for better starting. Your 6V starter will work fine, just don't grind on it for extended periods of time. Oh yeah, one last thing. Because you're reversing battery polarity, don't forget to reverse the ignition coil polarity too. This help?
Hey Steve thanks for the input, it's a good help. I'm on the right track with bulbs, fan motor, coil polarity, etc...I hadn't thought about the resistance of the coil itself. It is a "12v" coil the owner provided. I haven't pulled a part number off it but it appears to be an older OEM Ford part. I planned on a generic ballast resistor to the coil +. The owner also provided a new 12V solenoid, but it's a chineeseium thing without the second post to put 12v to the coil when cranking. I honestly wasn't worried about it - I figure the engine started on 6 volts at the coil it would start with the 9ish volts coming from a ballast resistor. But I've been wrong before...
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