gauge ohms test readings

aussie merc

aussie merc

Well-known member
does anyone know what the ohm readings are for a 39 mercury gauges someone did a bad 12volt conversion and fed the gauges 12 volts not six were slowly getting it sorted but now i need these readings so i can work out if the gauges managed to survive or i have to replace them
 
The ohm reading should not be a significant value for checking an original gauge. They do not work off of resistance, they are a current pulse device. The senders use points to vary the current duration (pluses) and the current duration heats a coil in the gauge which determines the reading. Very different from modern gauges. Not sure there is an ohms value for the gauges that would show it to be good or bad. One test is to connect a 1.5v battery to the gauge and see what reading (if any) you get. The 12v to the gauges may not have caused any damage if it was not over a long period of time. Again, the gauges and senders work off of current flow, not voltage, so may well be fine.
 
If you read the gauge with an ohm meter, the points will be closed and the reading should be around 10 ohms. That will show if the gauge wiring around the bimetal is still intact.
BILL WELLS is not open.
 
Be aware that the leads used with a multi-meter have a resistance in themselves. This should be determined beforehand, and the meter adjusted for it or it should be subtracted from the ohms readings taken to determine the true value. For example, on my cheap multi-meter, the leads have a resistance of .5 ohms.
 
hi thanks for the feedback ive tested the gauges with a tool call a gauge check and a multimeter got the readings of 15 ohms on the low side and 40 ohms on the high side so does anyone know of anyone whos selling replacement senders or has N.O.S for sale or at least the part Nos for the senders
 
J Seery got it right. Those year gauges do not work on the ohms principle and never will.
Each gauge is calibrated with the specific sender based on the bi-metallic "pulse" principle.
Here's some info.
https://www.fordbarn.com/forum/showthread.php?t=240841&highlight=gauges+work

Do a search of "How gauges work." and lots of helpful info. appears. Or, do an individual search on each gauge .e. "How temperature sender works." How fuel gauge works.
How volt gauge works. How Amp gauge works. How fuel gauge works.

It's pretty interesting to see the King Sealy design using only heat. Hope you are able to locate senders you need. Some senders may be interchangeable. For instance the early 1950 Ford 6V fuel tank senders can be adjusted to work with 1940 Ford Fuel gauge. You have to have the patience of a toothache when doing this as it's tedious.
 
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aussie merc said:
hi thanks for the feedback ive tested the gauges with a tool call a gauge check and a multimeter got the readings of 15 ohms on the low side and 40 ohms on the high side so does anyone know of anyone whos selling replacement senders or has N.O.S for sale or at least the part Nos for the senders
Click to expand...

No idea where you are getting these numbers, what would be varying the ohms measurements? Point (contacts) are either open or closed, so, zero or some minimum value of the heating coil. Are you sure you are working with stock Ford gauges?
 

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testing is easy disconnect sender attach [vdo] gauge check [ basicly it just a verible resistor] in place watch gauge dial up reading [high /low or center ] disconnect gauge check and check ohms with multi meter for correct reading however on reading the feedback these gauges work slightly differently to later ones and i will need to do more reading thanks again for all your input
 
aussie merc, The VDO gauge check tester you are using is for testing resistance type gauges only and is not for testing Ford King Seeley made gauges which as stated by others on here works on an entirely different principle. King Seeley gauges require a king Seeley sender to work correctly and accurately. Some people use the resistance type sender units with the King Seeley gauges but results in operation can vary from just OK to hopeless. Your best bet is to forget all the multimeter resistance tests and just connect all your gauges and original senders in the car and feed 6 volt power into them using an electronic voltage drop unit to drop the 12 volts to 6 volts and see if they are operating OK. The winding coils on the bi-metal strips in your gauges may have been overheated or cooked if fed with 12 volt power supply. They were designed to operate on 6 volts, not 12 volts. Doubling the voltage on them doubles the current through them causing overheating of the windings in many cases. Regards, Kevin.
 
any one know who has nos/replacement senders for oil fuel and temp or if anyone in australia can rework the gauges to resistance type
 
Good or NOS sender units are very hard to find these days. Gauges NOS come up on ebay quite often so keep checking. Have you connected up your gauges and senders to establish their serviceability. They might just be OK if you are lucky. If you want them "reworked" then find an instrument shop in Sydney who might be able to fit modern gage movements inside the original gauge housings with matching sender units. Would cost you quite a few hundred dollars to do that work. You really should check out your original parts first before getting into modifications unless you are building a modified car or hot rod. Regards, Kevin.
 
a working gauge beats a pretty picture every time and if it costs so what its still cheaper than a blown engine even better when it not only work right but looks right as well
 
Not that hard to test you gauges...just need a power supply that can put out 7v and in the 3+A range.
Start by hooking up the gauge and fuel sender...just series..from power supply to gauge...from gauge to sender...from housing of sender back to power supply...it doesn´t care about polarity.
Set the sender on low and wait...they are slow...then move sender to full...another cup of coffe while waiting...if the readings are good you now have a working sender to check the other gauges with.
Oil sender can be tested with compressed air....temp sender needs a pot on the stove and a thermometer.
Your evening is saved make some coffe and have fun :)
 
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If you for some mysterious reason really want to go 12v resistive and more modern 240 ohm range....take a VDO gauge cluster out of a early volvo 240...there was other makes like yasaki that won´t work...the gauge face plates and needles fit on them and they bolt right in...did a Jeep that way...but it was a real hybrid with an engine not to be mentioned....not my prefered way if i can choose.
I have both NOS and tested good used parts if you come up short...still think you should test what really is good or bad before starting to swap parts.
 
as i said a working gauge is better than none at all you got to remember im in australia not downtown deerbourn so there isnt a lot of spares on the ground so any lead is a good one
 
aussie merc said:
me again just curious does anyone know when ford went to resistance type gauges
Click to expand...

Per Deucemac 1985. Did you see all of the information I gathered together in a PDF? The attachment is from that PDF.
 

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