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Discussion Starter #1
So I think the quick question to this is does a +5vDC constant (vs. factory +5vDC pulsing voltage regulator) work for the factory gauges on a 67 mustang fastback?

Background:
I swapped my factory +5vdc pulsing voltage regulator to a homemade +5vdc fixed voltage regulator w/cap inline (found the mod/recommendation online). Wasn’t 100% that my factory voltage regulator was defective but heard this was a more reliable setup. Anyway, when I first did this install, I noticed that the temp gauge reacted a bit but only climbed 1/8 up and now it doesn’t work anymore. The fuel gauge never reacted with gas in the tank. I tested the wire that goes from the fuel gauge to the gas tank for continuity and checks out ok. Did the same with the temp gauge and that checked out as well. I also unplugged the sending line on the gauges and grounded it and both gauges climb to the top, which as I understand it tells me the gauges are ok.

I find it odd that both the fuel gauge and temp gauge both don’t which leads me to the common denominator of the voltage input and the fact that I switched from +5vDC pulsing to a +5vDC constant.

Btw, I don't mention the oil pressure gauge because its not hooked up.

thanks in advance!
 

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Quick answer: Yes

The original CVRs output is pulsed battery voltage and not 5V. Its simply a relay contact cycling open/closed/open/closed... With the car not running that would produce 12V pulses. If the car is running and the alternator charging properly then you would get 14+V pulses. When first turned on the CVRs do not cycle for about 2 seconds which puts a non-pulsing 12V on the gauges. That means the gas gauge needle (and all the others) will move more quickly and have enough time to almost reach the 'F' mark before the cycling starts and the response time gets really slow.

If the original CVR is working there is nothing unreliable about it. Its the new repros that quit after a half hour. I have never had to replace or fiddle with the original one in any car I have owned.

The pulsing is at a rate of about twice per second and its not a symmetrical off/on but the duty cycle varies to keep the effective (RMS) output voltage somewhere in the 5-6V range. The King-Seeley gauges were originally designed for 6V cars and the CVR allowed Ford to continue using essentially the same gauges after 1957 when they went to 12V. The gauges will work with DC but the calibration of the gauges may be off unless you have the correct DC voltage. 5V is a little low but they should still work although read a little lower than normal. The biggest difference will be that the gauges will be slow responding all the time, even when first turned on, since there will be not be an initial 2 seconds worth of 12V. That means several seconds before the gas gauge needle can make it to 'F'.

Each gauge may take as much as 1/4 amp of DC current. Provided your DC supply can do that your gauges should work on DC just as they did with the CVR.
 

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The details of it all are in US patent 2,835,885 issued in 1958 to King-Seeley Corporation, Ann Arbor, Mich., a corporation of Michigan.

The present invention provides improved electric gauging
systems in which a unitary voltage regulating device
delivers pulsating electric energy, at a substantially uniform
effective voltage, from a source of alternating, pulsating,
or direct current of variable Voltage, to operate
a plurality of electrically operated gauges for measuring
various physical conditions, such as liquid level, temperature,
pressure, or the like...
 

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Discussion Starter #4
Thanks! They're so slow to respond right now that I think I'll just go back to a standard CVR so its getting the 5-6v average it needs.
 
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I've had a problem periodically where none of the gauges work at all. I recently figured out that it is tied into the ignition switch. When the key is all the way to the right in the Run position, the gauges don't work. If I move it back to the left, they start working.

I've had an ongoing issue with the guages not giving full readings. The CVR failed and I replaced it. The new one worked, but only for the first couple of seconds, then the readings went down by ~half. The gas gauge being the only thing I could use as a guide. I since purchased 2 other CVRs and they all have the same behavior. I can't believe they are all bad.

I've checked the voltage to the CVR in the past and it is 12V. Any ideas on why these keep showing low?
 
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