| missouriron | -- 01-31-2015 @ 5:40 PM |
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I am changing my 38 V8 to 12 volts. I have Runtz electronic voltage reducers to use with my 6 volt original guages. Do I change polarity on the guages by attaching the + cable to the same terminal on the guages? Or, do I reverse how the cables(wires) are connected? Any advice will be appreciated. Ron Ron
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| Drbrown | -- 01-31-2015 @ 9:40 PM |
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You didn't note but I assume your exist 6 volt system is the stock set-up with positive(+) to and as ground. Normally, going to a 12 volt system one changes to negative(-) as ground. If the gauges register in the reverse of what they should, just switch the connections on the back of the three gauges. The voltage reducers you are installing are unaffected by this issue; they don't care which direction the current flows. Depending on the type of amp gauge you have, it does not need a reducer but the direction of the wire feed on the back of the meter may need to be reversed if the meter registers in the incorrect direction. Also, if you have a heater you'll need a different voltage reducer for that. This message was edited by Drbrown on 1-31-15 @ 9:43 PM
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| missouriron | -- 02-01-2015 @ 3:39 AM |
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Thanks for your reply. I am using the stock gauges. It has been a long time since I disassembled the wireing. I am having a hard time remembering how it was hooked up as a 6 volt system. The 2 gauges I am concerned about are gas gauge and oil pressure gauge. I don't want to start the newly rebuilt engine without knowing about oil pressure. However, I can wire in the gas gauge with reversed polarity and turn the ignition on. If the gauge moves, I will have wired it correctly. Thanks again for your comment. Ron Ron
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| missouriron | -- 02-01-2015 @ 5:08 AM |
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Thanks for your reply. I am using the stock gauges. It has been a long time since I disassembled the wireing. I am having a hard time remembering how it was hooked up as a 6 volt system. The 2 gauges I am concerned about are gas gauge and oil pressure gauge. I don't want to start the newly rebuilt engine without knowing about oil pressure. However, I can wire in the gas gauge with reversed polarity and turn the ignition on. If the gauge moves, I will have wired it correctly. Thanks again for your comment. Ron Ron
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| juergen | -- 02-01-2015 @ 9:15 AM |
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The only gauge that is polarity dependent is the ammeter. The others are heat elements so there is no need to reverse polarity. I'm not sure but the Rutz is a voltage drop so I believe you need one for each gauge (except the ammeter). As mentioned, the heater takes a much larger current draw, so the voltage drop resistor is much less and the current rating has to be much higher.
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| Drbrown | -- 02-01-2015 @ 10:02 PM |
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Sounds like you haven't accessed a published wiring diagram for your '38. I only have a '42 thru '48 Shop Manual so that's no help. If you don't have a Manual, shop around for one on the Ford forums or the Bay or Amazon. You'll probably get a lot of use out of it. I have Runtz voltage drop units on my '47 but they and the 12v conversion were done before my ownership so I don't have direct experience. Good luck and keep us posted.
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| DD931 | -- 02-02-2015 @ 7:07 AM |
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12 volts vs. 6 volts!!! This subject seems to have a life of its own!!!
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| TomO | -- 02-03-2015 @ 6:49 AM |
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The Oil pressure gauge and the fuel gauge are connected by a common bar and the Black with Green tracer supplies power to both of them. The wire goes on the terminal with the buss bar on the fuel gauge. The open terminal on both gauges go to the sending units. Here is a link to the wiring. If it is not clear, I will try to post a picture from the Service Letters. http://www.vanpeltsales.com/FH_web/FH_images/FH_electrical-pics/Flathead_Electrical_wirediagram1938-39car.jpg Make sure that you provide the proper voltage to the gauges or you will burn them out. You should also have your starter changed to 12 Volts. A 6 Volt starter's life will be shortened considerably if you use it with 12 Volts. Just to satisfy my curiosity, why are you converting to 12 volts? Tom This message was edited by TomO on 2-3-15 @ 6:54 AM
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