Posted By: repad
Fuel sending unit electrical question - 11/03/09 01:35 PM
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?
Posted By: RapidRobert
Re: Fuel sending unit electrical question - 11/03/09 02:00 PM
Yes ~5 volts. I'd check the VL under the dash & see whats shorted.
Posted By: repad
Re: Fuel sending unit electrical question - 11/03/09 02:02 PM
How do I check the volt limiter?
Posted By: RapidRobert
Re: Fuel sending unit electrical question - 11/03/09 02:12 PM
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.
Posted By: Andrewh
Re: Fuel sending unit electrical question - 11/03/09 02:52 PM
I never put a meter on mine, did you check with a light? it should blink if it is wokring.
Posted By: stumpy
Re: Fuel sending unit electrical question - 11/03/09 07:12 PM
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.
Posted By: Matt_Snowball
Re: Fuel sending unit electrical question - 11/04/09 08:52 AM
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.
Posted By: stumpy
Re: Fuel sending unit electrical question - 11/04/09 03:48 PM
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.
Posted By: Matt_Snowball
Re: Fuel sending unit electrical question - 11/05/09 08:27 AM
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 .
