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Posted By Discussion Topic: understanding ammeter -- page: 1 2     fordmerc 09-08-2010 @ 2:25 PM reply profile send p.m. New Member Posts: 180 Joined: Oct 2009 the problem: ammeter slowly moves to below midposition when ignition on (engine not started) Needle stays there through starting, running, and, when engine turned off, slowly returns to rest. Any suggestions where to start the troubleshooting? 37RAGTOPMAN 09-08-2010 @ 4:33 PM reply profile send p.m. Senior Posts: 1958 Joined: Oct 2009 fordmerc, is that a 39 MERCURY,? it would make a little easier if we knew, It sounds like the generator is not working,also the regulater,did it happen all of a sudden? check the brushes in the generator. see if black and worn, let us know, 37RAGTOPMAN, fordmerc 09-08-2010 @ 6:54 PM reply profile send p.m. New Member Posts: 180 Joined: Oct 2009 Yes, it is the '39 Merc. Generator = "rebuilt" Regulator = repro Probably going on since I started reassembly Brushes looked OK 23 miles ago (maybe additional hour idling) The ammeter behavior is so unusual that I would look for another instrument if it were not the original. trjford8 09-08-2010 @ 7:49 PM reply profile send p.m. Senior Posts: 4214 Joined: Oct 2009 Did you rewire the car? Perhaps you have the wire passing through the loop in the wrong direction. 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 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. 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 @ 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. 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. 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

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