Re: 1937 Wiring Issue
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Home away from home
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I would recommend checking the negative cable from the battery to the starter at the point it passes above the clutch/brake mount rod. There is a part of the body that my cable rubbed through and created a high resistance ground point. This was found during my motor rebuils while the engine was out.
I replaced my cable and repositioned the point of body out of the way. ( not a points car and not a fire hazard) LArry
Posted on: 2021/8/20 23:40
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Larry Reber
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Re: 1937 Wiring Issue
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Thanks, Larry. I'm working on it again today and will definitely check that out.
Posted on: 2021/8/21 10:04
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Roger Howe
Whitewright, TX 1937 120C Touring Sedan |
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Re: 1937 Wiring Issue
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Forum Ambassador
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Troubleshooting with a volt meter is sometimes tricky. It may take a current reading along with the volt reading as well as some deduction to decide if something else in a circuit is skewing the results.
Your meter could be reading through something that is connected and just sitting there but in perfectly normal condition. The meter has a high internal resistance and while it can measure voltage on both sides of an item, there is too much resistance in the meter to let enough current flow for the item to actually do anything. A good example would be reading thru a coil or a bulb filament permanently connected on one side. As long as the coil winding or filament was intact the meter would read the supply voltage on one side and then the same voltage would go thru the item and appear at the terminal on the other side as well as every other item on the car that same terminal might be connected to. Even though the voltage reading is present, the coil or filament would not do anything until a solid connection to the return side of the battery was made on that terminal to provide the current needed for the item to operate. With the partial voltage you are reading it could be normal voltage drop thru a resistance but at that low a voltage it could also be that a resistance to ground has developed on a wire or component also connected to the side you are measuring -- high enough to lower a voltage and provide a bit of current flow but not low enough to permit sufficient current to flow thru the component to energize the item. If you had a wiring diagram showing exactly which wires you have removed and what and where you are measuring that might help in narrowing down what else could be connected and worth looking into or what might be happening.
Posted on: 2021/8/21 11:36
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Howard
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Re: 1937 Wiring Issue
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Thanks, Howard. Here is what I have done thus far. 1) removed the wiring harness completely. 2) only connected the line that runs from the started solenoid to the ammeter, but only at the starter solenoid. 3) isolated all other wiring. The measurements still give me 2.50 volts across the system. I then took the harness and my 12-volt battery and connected the negative pole to that particular wire. With my voltmeter, I measured the current through that wire alone and it read 12.6 volts . I then measured current from the end of that wire through other wires and received measurements from 6 to 7.5 volts. I truly believe I have something amiss within the harness. My next step is to remove the harness wraps and check the individual wires. As stated, I truly think I have something definitely amiss. I do appreciate all of the information you have provided. I'll take your response and put it in my restoration notes. Thanks.
Posted on: 2021/8/21 13:28
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Roger Howe
Whitewright, TX 1937 120C Touring Sedan |
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Re: 1937 Wiring Issue
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Quite a regular
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You probably also should be aware that if you are using a DVM that that some of them tend to have some pretty questionable readings around our old cars.
Probably the higher quality DVMs are less prone to the problem. Even an inexpensive Radio Shack VOM will give you better results. I use a Simpson 260 just because I'm comfortable with it. YMMV Good luck.
Posted on: 2021/8/21 15:01
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Re: 1937 Wiring Issue
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Home away from home
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Thanks, Jim. I took your information and instead of using my DVM to check voltage, I used my test light with the terminal that was giving me issues on my harness attached to a 12-volt battery. I then touched the light to the other end of that wire from the battery and the light illuminated as expected. I then touched the ends of each of the other wires and no illumination occurred. I am going under the assumption that the DVM readings were caused by magnetic induction which was a result of current flowing through the wires and they were, as you pointed out, false readings. I have reinstalled my harness back into my car with the negative pole attached to the starter solenoid as per this model. When I touch the battery terminal to the positive pole there is no spark or anything that would tell me that current is actually flowing. I do really appreciate your input concerning this and hope you have a great week. Thanks again.
Posted on: 2021/8/22 15:46
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Roger Howe
Whitewright, TX 1937 120C Touring Sedan |
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