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EFV-8 Club Forum / General Ford Discussion / 1939 Deluxe fuel and battery gauges.

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Posted By Discussion Topic: 1939 Deluxe fuel and battery gauges. -- page: 1 2 3     1939ute 02-20-2011 @ 1:25 PM reply profile send p.m. Member Posts: 80 Joined: Apr 2010 Hello Tom and supereal, thanks again and I think I will just leave it as is and as suggested, just enjoy! Thanks for all the help. Cheers, John supereal 02-20-2011 @ 10:36 AM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 John: As the others have stated, increases in system voltage will affect the gauge readings. Modern cars used a simple device to stabilize the voltage to the gauges. I don't know if the type used on the early Ford Mustangs is still available, but it did the trick. Gauges on old cars were never very accurate, in the first place. They are kind of like weathervanes which show the direction of flow, but not the velocity. The only way I know of the get accuracy, if that is your "thing", is to install modern gauges and senders such as those by VDO and Stewart-Warner. I'd rather just drive and enjoy my cars. TomO 02-20-2011 @ 9:18 AM reply profile send p.m. Senior Posts: 7256 Joined: Oct 2009 Here is how the original sending unit and gauge works. Your after-market sending unit is just a variable resister. http://i168.photobucket.com/albums/u197/mercurytom/gasgauge.jpg The original unit allows for voltage fluctuations and slows the response of the sending unit to allow for the movement of the fuel in the tank during normal movement of the car. The variable resistor does not allow for these fluctuations, so you will see the fuel level rise when the voltage level rises, you will see it fall during acceleration and rise when stopping. Tom This message was edited by TomO on 2-20-11 @ 9:25 AM 1939ute 02-19-2011 @ 2:05 PM reply profile send p.m. Member Posts: 80 Joined: Apr 2010 Hello supereal, thanks, the battery stays charged when the ignition is switched off and it always starts fine! It's just until the generator recharges the battery, the fuel gauge level rises with the charge rate! Cheers, John 1939ute 02-19-2011 @ 1:58 PM reply profile send p.m. Member Posts: 80 Joined: Apr 2010 Hello Tom, thanks for that, I'll check it all out and see how go! I have made a note of ohms law, very helpful! Cheers, John 1939ute 02-19-2011 @ 1:46 PM reply profile send p.m. Member Posts: 80 Joined: Apr 2010 Hello Dolman, thanks again, I'll check to see if the sender has a tab or has a dedicated earth to chassis. Yes, I have only ever known the term earth! Cheers, John supereal 02-18-2011 @ 10:48 AM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 The starter solenoid has no part in energizing the gauges, or anything else except the starter motor. The gauges are fed from the accessory terminal of the ignition switch. The only parts of the car that are connected to the battery when the car is turn off are the voltage regulator, where the cutout relay isolates the battery, the interior pillar lights, and the feed to the lighting switch. It is common to use the input terminal of the solenoid as a tap for battery power, but the output side of the solenoid is connected only to the starter. If your battery discharges when the ignition and lights are turned off, you have a wiring error. TomO 02-18-2011 @ 8:52 AM reply profile send p.m. Senior Posts: 7256 Joined: Oct 2009 John, The operation of your fuel and battery gauges seems normal for the configuration that you have. Your Batt gauge shows the voltage of the generator output and it will rise with the engine speed until the battery is fully charged. Your gas gauge sending unit is a just variable resister and it does not work like the original King Seeley type. The amount of voltage dropped across the resister will be proportional to the voltage in the circuit. The gauge uses current in the circuit to heat a bi-metal strip. When heated this strip bends and moves the needle. The original sending unit had a similar circuit. Ohms law says current is voltage divided by resistance. The sending unit resistance will be fairly constant with a given amount of gas in the tank, so when the voltage goes up, there is more current in the circuit and the needle will move towards the full mark. Tom This message was edited by TomO on 2-18-11 @ 8:55 AM Dolman 02-18-2011 @ 7:36 AM reply profile send p.m. New Member Posts: 177 Joined: Dec 2010 If your gauge is working correctly, you should sleep well with the installation as is. As to a dedicated earth, the frame is the earth. If you have a good earth connection to the battery and you connected a wire between the tab on the outer ring of the sender and the frame, there is nothing more you can do other than run a wire from the tab back to the positive terminal of the battery and I think that would be much ado about nothing. If your sender does not have the tab, it is earthed through the tank via the mounting screws and I assume you have an earth wire from the tank to the frame. Your use of the term "earth" brings back a pleasant memory of when I was attached to the The Queen's Own Highland Camerons in the early 1950s. I was involved in radio communication and the term in that application made more sense than "ground". 1939ute 02-17-2011 @ 7:38 PM reply profile send p.m. Member Posts: 80 Joined: Apr 2010 Hello Dolman, thanks for your reply and correction, I will do the test you mention! I will need to make sure that the loom wires are the same and that the yellow wire is true to original. If not, I'll need to make sure I get it right! I take it from your correction that putting an earth onto the sender unit wouldn't cause any problems but I'm not sure if you imply that it would prove anything? Yes, I believe that the fuel gauge is indicating the correct level! When I filled it, it showed full but a bit over the full mark! However, as I have used the fuel, the level has seemed to lower as I have expected to as the fuel diminishes! I can only guess until I can gather confidence in the vehicle and venture out on a longer trip and watch the fuel level drop over a longer period! I have been slowly working through the issues! All those have been discussed on this forum! I do like to ask around before going in boots and all! Cheers, John

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