| 1939ute | -- 02-16-2011 @ 1:52 AM |
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I have just finished a full restoration on my 1939 Ute and have sorted most of the problems with some help from this forum! Thanks to all that have offered advice! I have now noticed that once I start the motor and as the battery builds up again, I notice that the fuel gauge level comes up with the battery amp gauge! I have put a new loom in and I haven't noticed it until I've been brave enough to fill the fuel tank! Any ideas anyone? Thanks. Cheers, John
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| TomO | -- 02-16-2011 @ 8:56 AM |
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John, we need a little more information. Is your Ute still 6 Volts, and do you have the original sending unit or an after market one? Tom
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| supereal | -- 02-16-2011 @ 9:40 AM |
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The gauges are fed power thru a common connection, and "look" for ground at the respective senders. Your description seems to indicate loss of voltage. The feed to the gauges is a black and green wire. As the ammeter seems to be involved, check the yellow wire from that gauge to the main junction of the loom. I suspect the ammeter is finding ground thru the same branch that feeds the other gauges when the ignition is turned on. Replacement looms often have strange paths. If you don't have a actual diagram for your car, I can send you one.
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| Dolman | -- 02-16-2011 @ 9:49 AM |
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John, Here's my theory. The fuel gauge is a voltmeter designed to read 6 volts with a full tank and measuring the voltage drop across a variable resistor. The resistor is connected across the battery. One lead of the meter is connected to the negative terminal of the battery and the other lead is connected to the armature (wiper)contact on the resistor. The position of the armature is controlled by the float in the tank. When the tank is full,the armature will be positioned at a point that the meter is across the entire resistor and will see 6 volts. As the fuel level decreases the armature will slide along the resistor until it reaches the opposite end of the resistor and will see no voltage. (Get out your gas can and start hiking.) At say half full, the armature on the resistor will be at a mid point and will see 3 volts. So, in my mind what you are seeing is normal. If the engine start discharges the battery to say 5 volts, the fuel gauge will initially be untruthful and as the battery is charged the gauge will gradually return to a reasonable state of honesty.
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| 1939ute | -- 02-17-2011 @ 1:43 PM |
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Hello Tom, thanks for your reply, it's still 6 volt and I have fitted an aftermarket sender unit to the tank! Both fuel and battery gauges are original! Thanks. Cheers, John
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| 1939ute | -- 02-17-2011 @ 1:50 PM |
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Hello supereal, thanks for that, I'll check all that out! I do have the original Ford Bulletin with the electrical diagrams in it. Thanks for the offer of sending the diagram though! Cheers, John
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| 1939ute | -- 02-17-2011 @ 2:02 PM |
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Hello Dolman, thanks for your theory and diagram! I do follow what you mean and it all makes sense! I've had it suggested to me that the sender unit may have a bad earth and to run a dedicated earth to it! I was going to try that but your theory has me thinking otherwise! I guess my main worry is that it won't short out and do some real damage to the loom! Thanks. cheers, John
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| Stroker | -- 02-17-2011 @ 2:04 PM |
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Gee folk, I wouldn't fix what ain't broke. We had 2-35 ton-and-a-half ranch trucks and a 36 lumberyard delivery 1-1/2 t with these, that were used in all kinds of weather and I don't ever recall draining the oil and finding evidence of water. I wouldn't powerwash the engine without capping the filler/breather tube, but I don't believe you will have a problem driving in a little rain. The fan blast gets pretty much deflected by the generator and carb base. I'd be more concerned about water getting into the generator or making your horns sound funny. If you insisted on driving in a deluge, you can always put it on backward.
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| Stroker | -- 02-17-2011 @ 2:48 PM |
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All: If the previous post doesn't make any sense at all, it is because I mistakenly posted it here, instead of under the Mystery oil filler question. I apologize to you for messing up a otherwise perfectly useful thread.
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| Dolman | -- 02-17-2011 @ 5:17 PM |
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John, A dedicated ground for the sender would discharge the battery while your back was turned. The schematic of a 39 shows the gauge's ground (earth) is supplied by the solenoid (relay) in the sender whose contacts close when the ignition switch is on. If the solenoid had a faulty ground it would not operate to close the contacts and the gauge wouldn't move at all. Unless, as Supereal suggested, it is finding a ground through some other path. To troubleshoot, I would disconnect the yellow wire at the sender end, tape it to prevent the possibility of an arc, and then turn the ignition switch on. If the gauge doesn't move, the loom is not the problem...if there is a problem. Does the gauge appear to show a correct fuel level after the battery is recharged?
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| Dolman | -- 02-17-2011 @ 5:21 PM |
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Correction A dedicated ground would not drain the battery if the ignition switch was off
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| 1939ute | -- 02-17-2011 @ 7:38 PM |
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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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| Dolman | -- 02-18-2011 @ 7:36 AM |
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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".
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| TomO | -- 02-18-2011 @ 8:52 AM |
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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
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| supereal | -- 02-18-2011 @ 10:48 AM |
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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.
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| 1939ute | -- 02-19-2011 @ 1:46 PM |
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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
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| 1939ute | -- 02-19-2011 @ 1:58 PM |
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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
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| 1939ute | -- 02-19-2011 @ 2:05 PM |
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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
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| TomO | -- 02-20-2011 @ 9:18 AM |
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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
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| supereal | -- 02-20-2011 @ 10:36 AM |
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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.
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| 1939ute | -- 02-20-2011 @ 1:25 PM |
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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
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