i'm attemping to use original `40 ford gauges with 12 volts using voltage drops and original senders. can anyone tell me which posts on the gauges are for power and which are for the sender? doing some checking with a 6 volt power source and my multimeter , i believe the ones with the strap on the are for power. also, is the voltage gauge really a volt gauge? it looks and acts more like a amp gauge....is this correct? if it is, anyway to hook it up?
You are correct, the straps are for power. Only the strap is hooked up to the voltmeter - note that some of the paper under the other nut is missing to provide a ground connection. The gauge itself provides some load to heat up the bimetal strip and move the needle - I think that makes it more like a voltmeter than an ammeter, FWIW. I used a single instrument regulator from a later Ford gauge panel ('59 F100) to provide the voltage conversion. You can get them new at NAPA of off any junkyard Ford gauge panel up to '79 or so. Mine has the needle straight up - not in the green - at 14.5V (verified with a multimeter). If you take the gauge itself apart, you'll see zero and span adjustment on back of the cup. I haven't adjusted mine, but I'm thinking that's the answer to get it to read correctly. I think the gauge would peg/burn at 12V, but I haven't tried it. Blown49 gave me some good detailed info about how those gauges were intended to work. They're huge files, but I can email them if you want. BTW, the '40 Ford owners manual has a decent schematic in it. Chris
thanks for your fast reply so it is just hooked up like a volt gauge? power to the post with the strip , and the other post(with no paper) to ground? do i have to use a voltage drop on the volt gauge too? do you have the napa part #?
The gauge hookup is just like you said. Strap for power - ground on the other side. I don't know if the instrument regulator is required for the BATT gauge or not. I think it should be, but my gauge is not reading correctly with it wired in. It works - just doesn't agree with the gauge face. I thought that I might be able to adjust the gauge to compensate, but I haven't tried, yet. Let me know what you end up doing. The NAPA p/n is ECH IR1. $31.49 online. This is a universal replacement part I think. Ford had several different brackets/wiring hookups over the years. Chris
Thanks for the info Chris, I was also having the same problem. I just wasn't sure if I had to run the amp guage thru the step-down.Greg
Read up on the operation of these in the original service bulletins - they do not use variable resistance sending units to change voltage to the gauge (which acts as a voltmeter - the variable resistance of the sending unit changes the reading) - like modern gauges. Instead, early Ford gauges all use heat. In both the sender & the gauge there is a bi-metallic strip with a wire wrapped around it - as current flows through it, it heats up the strip & due to the differing expansion rates of the two metals, bends the strip. At the sender side, this bending opens/closes the electrical contact that completes the circuit on the gauge side & works against pre-existing tension (fuel & temp) or pressure (oil press). At the gauge, the bi-metallic strip moves the needle. The voltmeter used in '40 is different - it just receives power & deflects based on voltage. If you insert a precision resistor of 60 ohms in series, it will work fine on 12V. There are two temp senders in the heads. The one with two contacts is simply a thermal switch. It completes the circuit as long as it remains closed. When it overheats (195??), it opens, sending the gauge full hot (normal position w/o power). The other sender has a bimetallic strip that reacts to engine temp instead of voltage. With all of this in mind, early Ford gauges should work fine on 12V. In theory at least, the higher voltages means the bi-metallic strips will heat up & deflect quicker, not more, & with the exception of the voltmeter noted above, should require nothing to switch to 12V. A reduction to 6V using any of the commercialy available devices should neither aid or detract from this operation. That said, I've not done it yet, but heard of folks who have!!
In theory, yes, but only if you run 'em straight off 12V & ONLY for the '40 voltmeter (battery gauge). If you have an ammeter, you need do nothing, but reverse the wires (***uming you're going from + gnd to - gnd).
thanks for all your input . i used voltage drops on the temp , oil , fuel and the battery gauge and they all seam to work fine. except the battrey gauge..it's like 40tudor said. the needle is straight up and not in the green. if i put 12 volts to it , it buries the needle i may have to do the internal adjustment he described
Your battery gauge is working correctly with the voltage regulator in there because the VR provides a constant 6 volts - the battery meter works as I mentioned, so it will NOT work with a voltage regulator (it'll probably indicate just under/left of the yellow band). You will need to find a precision 60 ohm resistor (most resistors are "approximate") to wire in series with the hot wire for it to work properly. Could probably get away with a small potentiometer (variable resistor) adjusted with a meter to 60 ohms. What do you think you'll be able to adjust inside? These are not like modern gauges, so there is no needle tension to adjust.
flat ernie , i will give the 60 ohm resistor a try..As for the insides of the gauge , i'm only going by what 40tudor said that there was some adjustment
Here's an oil gauge from a '59 Ford F-100 (pardon the ****py pics - it's early here). You'll note some similarities in construction to the '40 gauges. In fact, you can change the face plate and add the insulator/back plate and the only thing different is the needle (v-shaped and pointy in '59, flat and square tipped in '40). With a little care you can swap needles, too. Actually, I think it was Flat Ernie that got me to look into it. As far as function goes, you can use the instrument regulator from a 12V Ford to provide a pulsed signal with a variable resistance sender. This makes it look a lot like a flathead era sender as far as the gauge is concerned. The absense of a sender for the BATT gauge, I think, is what makes this one particularly challenging and maybe Ernie's solution is the best one. Here's my thoughts on adjustment: Look closely at the picture with the faceplate off. There are two small holes at 2 o'clock and 8 o'clock. 8o'clock adjusts the zero position, 2o'clock adjusts preload. Stick a small screwdriver in the back and turn it to move the little gear teeth that you see on the end of each lever. My thought is that you would adjust the preload higher to put the needle in the green instead of straight up if using the regulator. Otherwise skip the regulator and adjust the preload down to keep the needle from ******* (***uming the gauge doens't start on fire when you put 12V to it). Again, this is all theory as I haven't done it on mine. There may not be enough ajustment range. You might also consider bending one side or the other to get there, but it's going to be tricky. Chris
The truck gauges are modern design & I will likely switch to them one day. Most modern gauges work based on variable resistance at the sender. The gauge is actually an ammeter & by changing the resistance at the sender, the current flow changes through the circuit & deflects the needle. These gauges nearly always have a tension spring at the base of the needle that can be adjusted. I hadn't noticed the springs inside the '40 gauge before as I've never opened one up, but find it interesting that they adjust that way - makes sense though. I don't know if there's enough adjustment there for 12V - probably a fine-tuning/calibration type adjustment, but you never know... I think even if there is enough adjustment to get it to green on 12V, your scale may be off. The service bulletins have voltage ranges for each of the bands (again, don't have them to hand) & is why I guessed bottom of the yellow band for your 6V VR-tempered voltage (I think it's 6.1V for beginning of yellow). Realize that by doubling the voltage & not changing the resistance, your gauge readings are now half, so ***uming you could adjust the needle to the green on 12V, a one volt increase will change two volts worth of needle movement. I'm probably confusing you more... Early Ford guages also work on current flow of course, but deflect the needle based on heat (current) affecting the bi-metallic strip (visible in the second pic - wire wrapped around a bent strip). When you put the 6V voltage regulator on the battery meter, it wasn't varying the voltage like you do normally by revving the engine & bringing the generator up. Regardless of whether your 12V charging system was putting out 11 volts or 14 volts, the 6V instrument cluster voltage regulator puts out 6V, so you're only pushing 6V worth of current through the gauge circuit - hence, it's stable and vertical (probably just under the yellow band on the gauge face). It's working correctly. The 60-ohm number comes from the service bulletin itself. In the section describing the battery meter, it says the circuit is based on 60 ohms. Since you're running a 12V system now, by doubling the resistance, you should get your battery meter close by keeping the current heating it up similar. I'm in the middle of a move right now & don't have my service bulletins handy or I'd scan it in as it does a good job of explaining it all (much better than me!). If you want to run your original gauges on 12V, I think your best option for the battery meter is a 60-ohm resistor. The other gauges should work w/o any dropping resistor or voltage regulator, but keeping them 6V with the instrument regulator as you've done certainly won't hurt anything. Thanks for the pics, Chris! It makes it all make more sense!
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