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Author: Subject: How not to blow up my new fuel gauge…
Mr Whippy

posted on 18/9/09 at 09:13 AM Reply With Quote
How not to blow up my new fuel gauge…

Just got in a brand new cortina fuel sender for the Falcon, courtesy of the Old Parts Store (linky) who have been very helpful indeed in getting exceptionally rare parts so I may finish the car

Anyway, what I’m worried about is frying it the second I wire it up. All the other car electrics I’m happy with but it wouldn’t be the first time I’ve had a fuel sender go up in smoke though that was on another car.

I’ve got a new gauge I bought ages ago for another sender and would like to use that. But how do I check their compatible? What measurements do I need to do before risking wiring it up?

Unfortunately my electrical lecturer at collage spent most of the time in the cupboard drinking whisky rather than teaching, he had the shakes too

Your wisdom is needed, ta





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r1_pete

posted on 18/9/09 at 09:36 AM Reply With Quote
If you've got the voltage regulator in circuit, you should be safe. It drops the voltage to 8v I think, so you shouldn't have any problems with your sender.






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02GF74

posted on 18/9/09 at 09:38 AM Reply With Quote
usual wiring is:

supply ---- gauge ------ sender ----- 0 V

supply can be 12 V or for older guages, 9 V from a voltage regulator e.g. MGB, Land Rover and most British cars from 70s.

The gauge has a bi-metalic strip and this is what slows the needle otherwise it would be bouncing all over the place when driving.

the easiest way to tell if gauge and sender are compatible is to wire up as shown - not in the car - then move the arm to its max and min positions and observe the reading on the guage - allow a bit of time for it to settle.

usually the sender body is the earth i.e. connect to 0 V; the other conneciton is on an insulated 4.7 mm male terminal.

[Edited on 18/9/09 by 02GF74]






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Mr Whippy

posted on 18/9/09 at 10:15 AM Reply With Quote
cheers, wish I'd taken in the gauge so I could see its spec don't know what its voltage requirements are





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rallyingden

posted on 18/9/09 at 10:21 AM Reply With Quote
With the gauge disconnected measure the resistance across the supply terminal & sender terminal.
Measure the voltage on the wire that feeds the gauge.
Work out the current it will take by dividing the voltage by the resistance. This should be a very low figure as the wire size in the gauge will be very small.

If you get a high figure for the current ie amps instead of milliamps then the gauge is faulty.

If your happy that the figure is a low one connect the gauge to its supply wire and put the sender terminal of the gauge to earth you should see the needle start to move.

If all is ok then connect the sender to its terminal with the body to earth and move the float, this should move the needle correspondingly.

Hope that helps

RD

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Mr Whippy

posted on 18/9/09 at 10:40 AM Reply With Quote
quote:
Originally posted by rallyingden
With the gauge disconnected measure the resistance across the supply terminal & sender terminal.
Measure the voltage on the wire that feeds the gauge.
Work out the current it will take by dividing the voltage by the resistance. This should be a very low figure as the wire size in the gauge will be very small.

If you get a high figure for the current ie amps instead of milliamps then the gauge is faulty.

If your happy that the figure is a low one connect the gauge to its supply wire and put the sender terminal of the gauge to earth you should see the needle start to move.

If all is ok then connect the sender to its terminal with the body to earth and move the float, this should move the needle correspondingly.

Hope that helps

RD


great thanks I'll try that tonight, I'm all excited now ahh still over 4hrs to go





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rallyingden

posted on 18/9/09 at 02:22 PM Reply With Quote
Just got home and measured two fuel gauges I have, both smiths, both read 62.3 ohms so thats a tad under 200mA (192) dont have a sender to measure sorry.
By the way when I wire mine up I will be fitting a voltage regulator to stop readings changing as output from alternator changes, I will probably go for a 12V reg but I have not looked at this yet.
Hope that helps

RD

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Mr Whippy

posted on 18/9/09 at 02:39 PM Reply With Quote
Superb thanks very much for doing that I’ll measure what I’ve got and see if it’s close to yours before risking putting some power through it. I’ll also only use the battery for now to test it and look into this regulator.

Cheers





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