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Fuel sending unit electrical question #515096
11/03/09 09:35 AM
11/03/09 09:35 AM
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N.E Indiana
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repad Offline OP
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Put my mind at ease. I'm in the process of reinstalling a fuel sending unit in a 69 bee and upon checking the sending unit wire I find that it is flowing a full 12 volts. Is this typical? Isn't that wire supposed to be low voltage?

Re: Fuel sending unit electrical question [Re: repad] #515097
11/03/09 10:00 AM
11/03/09 10:00 AM
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RapidRobert Offline
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Yes ~5 volts. I'd check the VL under the dash & see whats shorted.


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Re: Fuel sending unit electrical question [Re: RapidRobert] #515098
11/03/09 10:02 AM
11/03/09 10:02 AM
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How do I check the volt limiter?

Re: Fuel sending unit electrical question [Re: repad] #515099
11/03/09 10:12 AM
11/03/09 10:12 AM
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With your VOM one voltage limiter terminal (input) should have ~12V (battery voltage). another terminal goes to ground (to a dash screw via the copper printed circuit strip) and the 3rd one needs to be 5V. I forgot which is which but eyeball the routing of the copper strips as the (5V) output goes over to the temp gauge also. If it is bad I would for sure get an electronic replacement type.


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Re: Fuel sending unit electrical question [Re: repad] #515100
11/03/09 10:52 AM
11/03/09 10:52 AM
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I never put a meter on mine, did you check with a light? it should blink if it is wokring.

Re: Fuel sending unit electrical question [Re: Andrewh] #515101
11/03/09 02:51 PM
11/03/09 02:51 PM
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denfireguy Offline
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Quote:

I never put a meter on mine, did you check with a light? it should blink if it is wokring.



A light will only tell you there is voltage there, not how much. You can get a digital volt/ohm meter from Harbor Freight for less than ten bucks. Since these regulators do go bad and will burn up your gauges, it would be less than the cost of a burned up temp gauge. Burn up your harness, and you are talking more than a precision laboratory grade meter.
Right tool for the job.
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Re: Fuel sending unit electrical question [Re: denfireguy] #515102
11/03/09 03:12 PM
11/03/09 03:12 PM
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Grand Prairie,Texas
stumpy Offline
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The test light will tell you if the limiter is working by flashing as that is how the voltage is reduced from 12v to 5v.

Re: Fuel sending unit electrical question [Re: repad] #515103
11/04/09 04:52 AM
11/04/09 04:52 AM
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Matt_Snowball Offline
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NO, no , no .

THe factory regulator does not reduce 12v to 5v . It just switches the 12v supply on & off regularly, like a turn signal unit, so that over a period of time, the gauges will 'see' an average of around 5v . If you put a meter on the line you should see a sequence of 12v , 0v , 12v , 0v etc etc .

An electronic replacement regulator WILL put out a constant 5v , but this is absolutely not what the factory item does.

The gauges will function roughly the same with either method, as they use hot wires and react slowly to any voltage change.

Last edited by Matt_Snowball; 11/04/09 05:06 AM.
Re: Fuel sending unit electrical question [Re: Matt_Snowball] #515104
11/04/09 11:48 AM
11/04/09 11:48 AM
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Yes,yes,yes. Did you not read the FLASHING part of my answer. That is how the 5v average is created by pulsation. I agree it's not a constan 5v.

Re: Fuel sending unit electrical question [Re: stumpy] #515105
11/05/09 04:27 AM
11/05/09 04:27 AM
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London England UK
Matt_Snowball Offline
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Stumpy I was not trying to contradict you, just to put right and explain the misinformation earlier in this thread.

You cannot put a voltmeter on the regulator output and try to read 5V , that's just not the way it works. The regulator, as you correctly say, does not put out 5v, it puts out an intermittent 12v .

Re: Fuel sending unit electrical question [Re: Matt_Snowball] #515106
11/05/09 01:41 PM
11/05/09 01:41 PM
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Grand Prairie,Texas
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Re: Fuel sending unit electrical question [Re: Matt_Snowball] #515107
11/05/09 06:23 PM
11/05/09 06:23 PM
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RapidRobert Offline
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Quote:

explain the misinformation earlier in this thread. You cannot put a voltmeter on the regulator output and try to read 5V , that's just not the way it works. The regulator, as you correctly say, does not put out 5v, it puts out an intermittent 12v .


That was me, so the oe ones will NOT read 5V, now I got it


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