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EFV-8 Club Forum / General Ford Discussion / 39 standard ammeter-oil pressure gage issues ?

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Posted By Discussion Topic: 39 standard ammeter-oil pressure gage issues ? -- page: 1 2     David Bentley 06-04-2012 @ 5:50 PM reply profile send p.m. Member Posts: 13 Joined: Mar 2010 Just installed new dash wiring harness and headlight harness .I ran the ammeter wire down from the top,then thru the ammeter gage,just the way all manuals show..I now have a oil pressure gage that wants to peg the needle and the ammeter shows a discharge when running the engine. I switched the direction the ammeter wire ran thru the gage,but the gage showed me making more amps when running,then even more with the headlights on...I also installed new ground straps from battlery to cowl and engine to cowl. I also have a new fully charged 6 volt battery... Any ideas out there ? 40 Coupe 06-05-2012 @ 3:31 AM reply profile send p.m. Senior Posts: 1685 Joined: Oct 2009 I would assume from your posting the oil pressure and amps worked properly before replacing the wiring?? The wire from the oil pressure gauge to the sender should be the same color on both ends (gauge and sender) Take the wire off at the sender and the gauge should not move. If it doesn't move and the gauge worked before rewire then it should be working now. It is possible the pressure is high at start up (cold) and will come down when hot. Do you have the battery connected properly + = ground? I believe the ammeter should read proper direction with the wire entering from the bottom and out the top(this is correct for 34-35). David Bentley 06-05-2012 @ 4:05 AM reply profile send p.m. Member Posts: 13 Joined: Mar 2010 40 Coupe, Yes, these were both working prior to the harness change. I do have the + to ground @ battery. The oil pressure gage never went this high before. The wires are the same on both ends. When I run the wire the ammeter up from the bottom, the needle jumps up when I turn on the headlights. I was thinking that the needle would drop slightly with the lights on ? TomO 06-05-2012 @ 6:55 AM reply profile send p.m. Senior Posts: 7264 Joined: Oct 2009 The yellow wire is the one that runs through the ammeter loop. The end that connects to the fuse block should be at the top of the gauge and the end that attaches to the starter solenoid should be at the bottom. The oil pressure gauge has the black and yellow wire attached to the terminal closest to the ammeter and a jumper strap to the fuel gauge on the other terminal. If your instruments are wired this way, you may have a defective wiring harness. You will have to use an ohmmeter to check for shorts in the harness and to make sure that the connections agree with the wiring diagram. Tom juergen 06-05-2012 @ 8:21 AM reply profile send p.m. Member Posts: 259 Joined: Jan 2010 You could be OK. Remember that the ammeter only measures the current going from and to the battery. When running the engine, the difference in generator and battery voltage will determine current through the ammeter. So to check for ammeter polarity, don't run the engine. Then the ammeter shou;d show discharge with the lights turned on and the engine off. If it shows a charge as you indicated with the engine running, the generator is putting out more voltage that the battery, therefore charging the battery and powering the lights. As for oil pressure, does the reading change with the engine running and the wire is disconnected from the sender? If not, you have a wiring problem as Tom described. supereal 06-05-2012 @ 10:45 AM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 Your gauge circuit is quite simple. As noted, the heavy yellow wire goes thru the ammeter loop on its way from the battery to the point where the lighting fuse is located, where a yellow/black wire feeds the ignition switch. A black/green wire connects to the bar that feeds the oil and fuel gauges. For the oil pressure gauge, a black/yellow wire goes to the sender on the rear of the engine, and a yellow wire reaches the fuel sender. If you don't have a wiring diagram for your car, I can post one. Before you change anything else, put a voltmeter across the battery poles and run the engine fast enough to close the cutout. You should see about 7.5 volts at the battery. I suspect that you will find the voltage in the system well above the level above. If so, suspect a problem with the generator, either with the third brush, on an internal short. Excess voltage will cause your problems, and damage the gauges. I have very little faith in new wiring harnesses. As you report that everything worked prior to the change, I'd look there. I've seen too many replacement harnesses that were inaccurately made and/or with the wrong color codes. 40 Coupe 06-05-2012 @ 10:46 AM reply profile send p.m. Senior Posts: 1685 Joined: Oct 2009 David: You are correct, the ammeter should read a discharge with the engine not running and the headlights on. If this is the case the wiring through the ammeter is in the correct direction. Is the fuel level gauge working correctly, if so remove the black yellow wire on the oil pressure sender and isolate it from ground, with the ignition switch "ON" the fuel level should work and the oil pressure should not move. If oil gauge does move the wire from the gauge to the sender is shorted to ground somewhere. This message was edited by 40 Coupe on 6-5-12 @ 11:01 AM David Bentley 06-05-2012 @ 11:46 AM reply profile send p.m. Member Posts: 13 Joined: Mar 2010 Thanks for all the above info.. I will try these suggestions this p.m. Could these issues be related at all to a possible bad ground strap connection ? The Fuel gage seems to be working corectly, as well as the radio , lights, horn, etc. Could I test the continuity of the oil pressure wire from end to end ? juergen 06-05-2012 @ 1:30 PM reply profile send p.m. Member Posts: 259 Joined: Jan 2010 Yes, A bad ground could make your generator put out more voltage if at and the regulator do not share the same ground. Check the voltage drops across each ground (at the ground wires and between the voltage regulator case and the generator case. They should not be over 0.1 volts. I always run a 6 volt ground straight to the starter and another ground wire from the generator to the engine (long with the stock ground from the engine to the firewall). Before you test the continuity of the oil pressure wire, test for a short as Tom suggested. Disconnect the wire from the sender and the gauge. I have a long test wire with alligator clips that I use to run from one end to the other to permit my ohmmeter to test for continuity (less than an .01 ohm resistance in this case). supereal 06-05-2012 @ 3:07 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 The '39 standard uses a cutout, rather than a regulator.

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