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Posted By Discussion Topic: understanding ammeter -- page: 1 2     40fordor 09-16-2010 @ 11:48 AM reply profile send p.m. New Member Posts: 116 Joined: Oct 2009 I had a somewhat simular experience with my 40. The charge rate was always at the border between the green and yellow part of the gage. After having my regulator and generator checked by a rebuild shop and found OK, the problem turned out to be an old slipping fanbelt. By the way (for TomO) a B51 belt was the best fit. Don TomO 09-11-2010 @ 7:53 AM reply profile send p.m. Senior Posts: 7250 Joined: Oct 2009 Your meter is reading very low, it could be due to a poor grounding connection or a defective gauge. Try testing the voltage by connecting the + lead of your meter to the grounded connection on the fire wall and the COM or- meter lead to the hot side of the gauge. It should be the side closest to the drivers side of the car. This will check out the grounding of the dash board and instrument cluster. NOS gauges are still around and sell for about $15-$25. Baxter Ford may have one for your car. Tom fordmerc 09-10-2010 @ 12:56 PM reply profile send p.m. New Member Posts: 180 Joined: Oct 2009 After all is tested, everything works OK except the BATT gauge. Voltage across the gauge is 7V - same as at battery terminals. Another '39 Ford confirmed the slow movement, so that's the way it must be. I guess the needle just rests a little lower on the scale after 71 years. 37RAGTOPMAN 09-09-2010 @ 4:36 PM reply profile send p.m. Senior Posts: 1958 Joined: Oct 2009 if you want to test the generator to see if it works, remember it is a DC electric motor, so, what you do is dissconnect the fan gen belt, take all the wires off the generator, take a test lead, 10 gauge, and run from the neg terminal battery , this should be the hot side since it is positive ground, run the wire to the arm terminal ,from the neg terminal the generator should spin, you are making it motor, if it does not motor, it will never charge, just touch for a few seconds 10-20 should be enough for the test,to see if the REBUILD is good, hope this helps,37RAGTOPMAN and KEEP on FORDIN,,,!!! TomO 09-09-2010 @ 8:54 AM reply profile send p.m. Senior Posts: 7250 Joined: Oct 2009 The stock 39 Merc used a battery gauge. From your description of the problem, it sounds like your generator is not charging. The marks on the gauge are : L = 2 volts, line left of the N is 6 volts, the N range is 6.75 volt at the left end to 8.25 volts at the right end, the line marked H is 9 volts. To check if the problem is the generator or the regulator, first try polarizing the generator by removing the wire from the field terminal of the regulator and touching it to the battery terminal momentarily. If the generator does not charge when the wires are back in their normal positions, use a jumper wire to connect the arm terminal to the field terminal of the regulator. The battery gauge needle should move to the right as you speed up the engine. Tom trjford8 09-09-2010 @ 8:08 AM reply profile send p.m. Senior Posts: 4214 Joined: Oct 2009 I now recall that the 39-40 Merc. used the same gauge as the 39-40 Fords. The only difference was the color of the gauge face.The gauge was called a "battery gauge" or voltmeter.According to the V-8 Club's 38-39 book the voltmeter came on cars equipped with the two brush generator.Towards the center of the gauge face you will see an "N" with a short band of color that contrasts with the gauge face. If the generator is operating properly and the battery is in good condition the needle on the gauge should be somewhere in the band of color. 39 Ken 09-09-2010 @ 6:43 AM reply profile send p.m. Member Posts: 380 Joined: Oct 2009 My bet is it is a voltmeter. Your description is exactly how my '39 Ford voltmeter works. Maybe someone familiar with the Merc will chime in here. fordmerc 09-09-2010 @ 5:35 AM reply profile send p.m. New Member Posts: 180 Joined: Oct 2009 All new harness. I don't know what kind of meter is installed. The "slow" movement is more like the gas gauge than any ammeter I've ever seen. The movement isn't really negative, but rather movement from resting on the left side with a slow rise to a point still to the left of center and then staying there engine idling or revving . This is really odd. I guess I must find out if the generator is really working. There is a new (repro) regulator installed, perhaps it isn't working either. Can I use a multimeter to test these? 39 Ken 09-09-2010 @ 5:06 AM reply profile send p.m. Member Posts: 380 Joined: Oct 2009 Probably a moot point but the '39 Ford is equipped with a battery condition gauge (read Voltmeter), not an ammeter. Is the gauge in the '39 Mercury definitely an Ammeter or are they equipped like the Ford? Your description of how it operates sounds like a Voltmeter. Johns46coupe 09-08-2010 @ 11:14 PM reply profile send p.m. Member Posts: 68 Joined: Apr 2010 One word in your description of the problem puzzles me: "slowly". Most ammeters I've seen move instantly. Going negative when the ignition is on but car not running sounds normal. Staying negative after starting sounds like you are not seeing the effect of the generator, because of the generator not working, the regulator not working or a wiring problem. But still, the slow movement puzzles me. Are your other gauges working correctly? John

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