| fordmerc | -- 04-28-2010 @ 5:42 PM |
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'39 problem: With ignition switch ON, wire from ignition switch through resistor shows lots of current (blew my multimeter fuse) (engine not running).With wire to coil disconnected, that terminal on coil is grounded. Is this right? The odyssey started because with ignition switch ON, smoke and smell come from under the dash. I did not do well in physics class so I need help and comments.
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| jerry.grayson | -- 04-28-2010 @ 6:28 PM |
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I don't understand your comment about the wire from the coil disconnected, that terminal grounded?? Anyway, it sounds like you have a dead short somewhere.
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| deluxe40 | -- 04-28-2010 @ 6:30 PM |
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Sounds like a short between the ignition switch and the coil. Given that the smoke and smell come from under the dash, I'd guess it is the wire between the switch and the resistor or the resistor itself. I would disconnect the battery and pursue the problem with an ohm meter. Check to see if the terminal on the switch that goes to the resistor is grounded. If so, disconnect the wire at the resistor and see if it is still grounded, etc. The problem has to be in the ignition switch, the wire to the resistor, the resistor, the wire to the coil, or the coil itself. Eliminate one at a time until you find it. On a second reading of your question I am thinking that the terminal on the coil is what you found grounded. That could be normal if the points are closed. The circuit goes through the primary windings on the coil and through the points to ground. I'd still proceed as described above (with the wire to the coil and the battery disconnected). This message was edited by deluxe40 on 4-28-10 @ 6:34 PM
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| TomO | -- 04-29-2010 @ 7:20 AM |
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If your points are closed or shorted you will have lots of current flowing through the ignition resistor. A shorted condenser will also cause this problem. Use your voltmeter to check the voltage at the input to the coil. Tap the starter to see if the voltage changes from about 3.5V to about 6V. If it does everything is normal. If it doesn't, check the condenser and the points. Tom
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| supereal | -- 04-29-2010 @ 11:48 AM |
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Do you have a wiring diagram for your car? It is a required "road map" to tracing your wiring. I agree with the others it is likely you have a short in the circuit between the output of the resistor and the coil. As the smoke and smell came from under the dash, look for obvious signs of burned wires or connections. The coil is grounded thru the points when they are closed. When they are open, you will read battery voltage at the coil. It is nearly impossible to troubleshoot using the ammeter part of a multimeter because most can handle only ten amps or less. The fuse saved your meter. Use the ohmmeter portion to check for shorts. Put the meter on the 1X scale and test the wires both for continuity and for a ground to the body of the car. If you need a diagram, I can post one.
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| fordmerc | -- 04-29-2010 @ 6:40 PM |
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I have the wiring diagrams, have annotated them in color and will proceed with multimeter in hand to go step by step. Thanks
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| 37RAGTOPMAN | -- 04-30-2010 @ 5:19 AM |
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hi fordmerc first thing is disconnect the primary wire going to the coil,on the coil-distributer itself, this will rule out if coil-distrubuter is your problem, turn the ignition switch on, and check for voltage on the end of that wire,, should be around 3 1/2 volts, make sure you turn on and off a few time to see if the ignition switch is ok, also.you shoulod see the needle on the meter go back and forth, if you take the wires off the back of the ignition switch, there are 2 screws that hole it together,if you remove them the switch will come apart, you can examine for any problems, also you can clean the brush , and with a piece of flat glass and a piece of 320 fine sandpaper take the bakelite piece that has the brass contacts and hold flat on the glass with and draw the switch back and forth till it is flat, the brush wears gooves in the switch,[ over years,] and brass contacts,this will flaten out the baklite piece, if it is to worn find a replacement, you can also add tension to the brush brass pieces by carefully bending them to add a little tension, if the dist is your problem, it can be a few different possibles, one problem, is we had a guy got stuck because the of the leather diaphram [ the vacuumn advance in the distributer grounded,just rotted away, does the car run,? you never told us, the more info, the EASIER it is to figure out, is the wiring new ? is it old and frayed, maybe gounding out along the way, is the primiary wire going though the metal conduit, you should examine the wires carefully, and trace the wires, also is there any other wire connected to the ignition side of the ignition switch,? if so disconnect that and check the circuit again, and then recheck, the resister does get hot,especially with the car not running and ign on, points will burn out,will build up a carbon on them , and causing them not to arc,so no starting, hope this helps, looking for a comeback on your problem KEEP ON TRUCKIN,,,,,,!!! 37RAGTOPMAN
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| fordmerc | -- 04-30-2010 @ 6:31 AM |
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I'm headed to the old garage; In answer to the question the car starts and runs, all new wiring, rebuilt coil, rebuilt generator, rebuilt distributor, new battery. Everything has been torn apart and reassembled. All gauges and switches worked on the bench. I will retrace wire connections and circuits again. I am also going to check each connector post for a short. Obviously, I didn't do well in physics class and found electricity shockingly complex. Thanks to all for help.
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| supereal | -- 04-30-2010 @ 11:28 AM |
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The last time I saw smoke from under the dash of one of my cars, it was caused by a short at the ignition switch. A terminal on the wire to the ignition had come in contact with metal case of the switch.
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| fordmerc | -- 04-30-2010 @ 2:57 PM |
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additional follow-up: New resistor on resistor-fuse block is burned - that's probably where the smoke and smell came from. Voltage at the primary wire is 7V. Voltage across that resistor (whether or not it is isolated) is 7V (same as battery). Now, when I test the old original resistor on the bench, I get the same readings for voltage and continuity. Of course, I do not know if that resistor ever worked. I had checked the ignition switch, but I will go back through it as suggested by supereal. This is a contemplative hobby.
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| TomO | -- 04-30-2010 @ 5:36 PM |
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Does the voltage at the primary connection at the coil vary when you crank the engine? It should vary between 6 volts and about 3.5 volts. If it doesn't disconnect the coil wire and check the voltage, it should be battery voltage. If it is about 3.5 volts there is a short to ground either at the resister block or the wire going to the coil. The purpose of the resister is to reduce the voltage going to the coil. If the ignition is left on and the points are closed, the resister will get very hot and start to smell. Tom
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| deluxe40 | -- 04-30-2010 @ 6:09 PM |
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At this point I need to go back to square one and ask "How long was the ignition switch ON with the engine NOT running before you smelled smoke?". And, also, "Did you smell smoke when the car WAS running?" It is possible that nothing is wrong (you said the car runs) except that the ignition switch was left on with the engine not running and the points happened to be closed.
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| BrianCT | -- 04-30-2010 @ 7:04 PM |
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Was the resister new? I have seen a post somewhere that a new resister may smoke when first used.
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| supereal | -- 05-01-2010 @ 8:51 AM |
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The ignition resistor is made from Nichrome wire, the same kind used in toasters, so it can glow red hot without damage. Check the resistor with your ohmmeter to be sure that it isn't open. Repro resistors are often inferior, with end terminals that come loose from the expansion and contraction of the winding, and may need to be recrimped and soldered.
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| fordmerc | -- 05-02-2010 @ 4:39 PM |
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I have a new resistor; the ignition switch was on for 5-7 min before the smell; the car ran for 15 minutes but I don't recall if I smelled anything ( I was too excited to have it running) The resistor (new and old) has continuity from end to end and no resistance. (that doesn't seem right!)In the AM I will check voltage as I turn the engine. The coil wire is 7V. The possibility that a new resistor just smells and smokes provides an unnerving experience to a novice; I would love to have that as the sole explanation for my anxiety. Thanks to all for much help all help appreciated.
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| supereal | -- 05-03-2010 @ 6:20 AM |
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Most new resistor, particularly repros, smell hot and smoke when first installed, perhaps like curry powder (just kidding). The resistance between units varies, but checking with the meter set on low ohms scale, you should see a reading between the terminals. The unit functions as a kind of elementary voltage regulator. As system voltage goes up, the resistor gets hotter, thereby increasing the resistance to protect the points and coil.
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