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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 02-16-2011 @ 1:52 AM reply profile send p.m. Member Posts: 80 Joined: Apr 2010 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 TomO 02-16-2011 @ 8:56 AM reply profile send p.m. Senior Posts: 7385 Joined: Oct 2009 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 supereal 02-16-2011 @ 9:40 AM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 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. Dolman 02-16-2011 @ 9:49 AM reply profile send p.m. New Member Posts: 177 Joined: Dec 2010 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. 1939ute 02-17-2011 @ 1:43 PM reply profile send p.m. Member Posts: 80 Joined: Apr 2010 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 1939ute 02-17-2011 @ 1:50 PM reply profile send p.m. Member Posts: 80 Joined: Apr 2010 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 1939ute 02-17-2011 @ 2:02 PM reply profile send p.m. Member Posts: 80 Joined: Apr 2010 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 Stroker 02-17-2011 @ 2:04 PM reply profile send p.m. Senior Posts: 1460 Joined: Oct 2009 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. Stroker 02-17-2011 @ 2:48 PM reply profile send p.m. Senior Posts: 1460 Joined: Oct 2009 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. Dolman 02-17-2011 @ 5:17 PM reply profile send p.m. New Member Posts: 177 Joined: Dec 2010 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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