I’m helping my brother with the electrical on his project 51 Shoebox. He bought it with a small block Ford 289 and a C4 installed but nothing else. No wiring, no driveshaft, linkages, etc. He is planning to use the 289/C4 but would like to retain the original gauge cluster. We will convert to 12 volts with new harness and use the temp, oil pressure sensors on the 289 which brings me to my question. Anyone out there done this before? I assume I’ll need a 12 to 6 converter. Does anyone have an original wiring schematic for this car? I’m very familiar with automotive wiring I really just to better understand how the original gauges operate.
If you are using the original 1951 gauges, you want to use the original 1951 sensors, so they'll work. Ford converted their cars to 12v in 1956, and at that time, they started using a thermal voltage limiter for the gauges. I'd suggest using that. For the speedometer, you'll need a cable that will fit into the new transmission. One for an early 60s Ford car should work. Make sure it has the "slug" at the transmission end (you'll also need to get a gear and clip), and a 5/8" screw connection at the speedometer end. Later cars used a clip retainer at the speedo, so the later cables won't work. And earlier cars used a threaded connector at the transmission end, so earlier cables won't work.
A reproduction Ford Shop Manual (available on line) will have the original wiring schematic included. Aftermarket wiring harnesses will include installation instructions, and good wiring kits will have the wires marked about every 6". Squirrel is right, use an original Ford under the dash voltage reducer. Ford used these up into the early 70's, and only requires one for all the gauges. The original fuel tank sender will work on 12 volts, and the ammeter will also as long as it wire it senses runs in the correct direction. A SBF oil pressure one wire sender designed for gauges works. A temperature sender for a flathead right bank is what you need. Try to find an original King Seeley unit, as it will give you the best reading. The Ohms on the aftermarket ones I have tried are too high, and cause the gauge to read high even at cold. Depending on which intake you have will determine if the sender will clear the inside of the head without bottoming out, so you may need an extension fitting.
Thanks guys. Since squirrels suggestion to use original sensors (why didn't I think of that....) I've been doing some research and Bangingoldtin has confirmed what I've learned. I did find a wiring schematic on-line. My brother already purchased an aftermarket wiring kit. So my plan is to get the senders I need and bench test things first. Always easier to resolve issues on the bench rather than laying on your back under the dash. I don't have the gauge cluster in front of me. Is the ammeter a physical connection or a current sensing set-up?
Unfortunately, it's a physical connection and the early generator ammeters are generally limited to a max 30 amp input matched to the generator's output. Virtually any OEM-type alternator can exceed this under the right conditions, so this can be a fire waiting to happen. I'd strongly recommend converting to a voltmeter. A ammeter is the preferred gauge for a generator because of the physical differences from an alternator. It will give more useful information as to the health of your charging system. A voltmeter will be better for an alternator for the same reason, minus the high current that can cause fires.
you might also consider using the existing ammeter as a shunt ammeter (wire it in parallel with a larger wire that goes from the battery to the rest of the electrical system)...it won't tell you as much as a voltmeter, but it will look right in the dash. Or leave the ammeter disconnected, and install an idiot light for the alternator. Or just don't have anything to tell you whether or not it's charging, besides the brightness of the lights. Most guys don't put enough miles on their hot rods or customs to wear out an alternator....alternators mostly just work.
1956 was a strange year for Ford. In 1956 Ford went to 12V with 12 V gauges. Fords 12V gauges proved problematic so in 1957 Ford went back to the 6V "King Seely" gauges and senders they had been using for years. To accomplish this Ford used a thermal voltage limiter that Squirrel mentioned. Ford retained the 6V style King Seeley gauges well into the 1990s on some vehicles. I second Squirrel's suggestion and do it like Ford did with the thermal voltage limiter/reducer that is found behind the gauge cluster on Ford cars. It may be more user friendly to use this from a 1960s car as later Fords use a printed circuit board. These are available new from Ford parts suppliers such as C&G Ford. In theory a 1960s 289 King Seely temperature gauge sender should work with the 1951 gauge. It may be slightly out of calibration but it should work. Now a 1960s King Seely indicator sender "Idiot Light" will not work with the 1951 gauge or even the 1960s gauge for that matter. Make sure in the sender is for a gauge not a light. It's best to use a genuine Ford/King Seely sender as the repro units can be troublesome. So you should be able to use either the 1951 sender or a 1960s + sender as long as it's for a gauge. The 1951 oil sender should be compatible as long as it has room to fit. It is a fat unit. the 8BA sender was a 80lb sender so it should work OK on a 289. Like the temperature gauge a later sender will work as long as it was for a gauge, not a light. Ford did run a Generator on the SBF through 1964. I do believe in 1965 you could get an alternator or generator with the new alternator being standard equipment in 1965.
I found out recently that Ford did use alternators as standard equipment as early as '63, just not across the full line. '63 full-size Mercurys had one, I discovered this after buying a '63 gauge cluster. Mercury did full gauges on various models '63-65, and all of the big Merc clusters I saw for sale had the amp gauge marked as for a 'alt', not 'gen'.
51 had an induction type factory amp guage. The wires are not physically connected, the wire just lays behind the guag e in a trough. The wire will have to run across the back of the guag e in the right direction to show a charge or discharge.
For a bit of information I learned on this board, (I'm using a regular 12V GM temperature sensor) somebody said to put a 100 ohm resistor between the sensor, connected to ground. It worked. But I can't explain why. As for the gauges, the other gauges have a 12v/6v voltage reducer except the ammeter except for the ammeter. I installed a "parallel path" as suggested before with a smaller welding cable (4 gauge) since the ammeter "loop" on the back will not take anything larger than 3/8" diameter. I fused the cable on BOTH ends with 50 amp fuses just in case. The cable is good for 150 amps. I have a 125 amp alternator, but only part of the flow goes through the ammeter. Your brother did the right thing by getting a rewire kit. I used a "Painless" kit, and it was excellent. Don't ask my how blinkers/tail lights/parking lights work, but when I hooked it all up, everything worked the first time. If you'd like to see "part" of what I did, check out the link below. And if you want to see what it took to build the whole car, click on the "home" button on the upper left to get to the home page and then you can see the entire building process...This gallery is one of 58 on my website about all sorts of things that I did related to shoebox resurrection. You might look at the gallery named "tips and tricks" that addresses some items related to the dash. I made a mistake thinking it would be cool to install ultraviolet dash lights,.. they are waay tooo weak. https://49fordcoupe.smugmug.com/Wiring-the-Car/ Here is a link to Tips and Tricks which has some information about the dash and what "happened" there.. https://49fordcoupe.smugmug.com/Tips-and-Tricks/
That's not true for all of them. That's what I thought because Ford seemed to favor that type but virtually every one I saw for sale on eBay had wire connections on the ammeter...
I have seen both types of ammeter gauges for the 49-51 dash. In my limited research in the past, it seems the post type was used in 49 and 50, with the change to the inductive type in 51, continuing until 54. My 53 has the inductive type, which consists of two barrel hoops on the back of the gauge for the wire to pass through. If your alternator is more than 60 amps, I would run a parallel wire from the alternator to the battery. I did it that way with my 100 amp and the ammeter still functions well enough.
The Ford ammeter senses the magnetic field in the wire and has no physical connection. I just put a 50 dash cluster in the center of my Model A and had to struggle a bit mentally about how to run the wire through the ammeter. The ammeter needs to sense the current going into and out of the battery. You can't just run the alternator output wire through the ammeter. That will tell you if the alternator has output, but you won't be able to see loads like lights etc. It's been about a year since I wired it, but I believe I ran the alternator output wire to junction block and ran all power feeds to the ignition and fuse block off this junction. I then ran two 10 or 12 gauge wires from the junction block, through the loop on the back of the ammeter. I would have run an 8 gauge wire, but I couldn't bend it enough to get it through the loop in the space I had. The other end of the wires went to the starter battery terminal where the positive battery cable was attached. Remember that all the electrical devices except the starter are being fed by the wire going through the ammeter loop so it needs to be of sufficient gauge.
Thanks for all the reply's, I'm learning a lot. I've restored and rewired a lot 65/66 mustangs and they use what is called a "Constant Voltage Unit" to keep the gauges (fuel, water, oil) reading the same regardless of the Alternator/Battery voltage. As I recall the output of these were 5 volts, but its been a while since I measured one. Its likely what was termed above as the "Thermal Voltage Limiter/regulator". This was before solid state electronics found their way into cars. I've got a bunch of old mustang senders so I'll play around a little bit and see if I can use any of them with my brothers gauge panel. Boy is he going to owe me..... I'm a strong believer in a voltage gauge rather than an ammeter. I can tell right away if the alternator is working if the voltage is around 14 volts. I'll probably do the parallel path method for the ammeter and have my brother install a separate voltage meter. Or do as I have done on my 66 Mustang and retrofit a volt meter in place of the ammeter in the original cluster. It looks stock from a distance but tells me more than the ammeter.
The ones I saw were definitely '51 clusters as they had the gold speedometer center, which was '51 only as far as I can tell. And Ford was famous for 'using up' remaining parts stock before putting a new part onto the line, so there wasn't always a 'clean' break by year. It could also make a difference as to where the car was assembled, there could be minor differences between plants. Out of curiosity, I checked the four '50-51 Merc clusters I have. Every one has a inductive-type ammeter rather than the post type, but Mercury usually got the 'better' parts before the Ford did. I'm not a fan of using a shunt on a ammeter as these weren't all that accurate to start with and a shunt only makes it worse. I'd go with an idiot light over a shunt.
My '49-'51 Ford shop manual states and shows the magnetic (induction) style ammeter used on '49-'50 cars, and the wired two-terminal ammeters for '51, which my '51 has.
Flathead_Electrical_wiring1949-50car.jpg (800×685) (vanpeltsales.com) Flathead_Electrical_wiring1951car.jpg (776×692) (vanpeltsales.com) Bingo!
Answers to this seems to be all over the place. I don't have a '51 gauge in my hands, but I do have a '50 gauge right here and it has an inductive loop the wire goes through, so no physical connection. I also have a '53 Lincoln in the shop today and it also has an inductive loop on the back of the ammeter. Again, not a '51 gauge but I think if you wanted to use an original looking gauge it might be possible to find an inductive style gauge and use it in your cluster if the one in yours is indeed a positive connection style gauge.
Look over those wiring harness schematics I linked from from Van Pelt. 1950 shoes the inductive loop. 1951 shows a connection.
Does anyone sell re-pop gauge clusters with modern guts for the shoebox? I've seen them for my car, curious how far they may go back and what you want to retain for having an OG look.
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