| 49FH8 | -- 07-24-2011 @ 8:52 PM |
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I recently purchased a beautiful 49 Mercury. It has been converted to a 12v system. The headlights didn't work. I replaced the fuse and they work except the wire terminals at the switch get extremely hot. Is this normal? Is it an issue having a 12v system with a 6v switch? Also, the temp gauge doesn't work...where is a good place to find one or have it repaired? Thanks for any help.
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| TomO | -- 07-25-2011 @ 7:04 AM |
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A switch is not voltage sensitive. It should work equally well with either 6 Volts or 12 Volts. The terminals are getting hot due to excessive current or excessive resistance. Excessive current can be caused by Halogen lights or a leak to ground due to poor insulation in the wires. Excessive resistance can be due to wiring that is too small for the current or corrosion. To check out whether the Temp gauge or the sender is bad, remove the wire from the sender in the left head going to the gauge and ground the wire. Turn on the ignition and the gauge should move towards the cold indication. Do not leave the switch on for more than a few seconds with the wire grounded as you will damage the gauge. If the gauge works, reconnect the wire to the terminal that also has the right side sender connected to it and then repeat the above test. If the gauge now goes to the cold side, the left sender is defective. If it stays at the hot side, either the right side sender is bad or it does not have a good ground. Try installing a jumper from a good ground to the housing of the sender. Tom
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| 49FH8 | -- 07-27-2011 @ 5:20 AM |
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Tom, I appreciate the info and will check it out this weekend. Many thanks, Steve
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| 49FH8 | -- 07-27-2011 @ 4:32 PM |
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Tom, I changed the headlights to a non-halogen type and still getting heat at the fuse and switch terminals. The wiring seems to be fairly new and of adequate size 16-18 gauge. Any suggestions on best way to troubleshoot a leak to ground - I am mechanically capable but electrically handicapped. I will soon test the Temp gauge based on your instructions. It's hot down here in Houston and can only stay in the heat for short periods to troubleshoot. Thx Steve
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| 49FH8 | -- 07-27-2011 @ 5:09 PM |
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Tom...Great instructions for troubleshooting! The gauge is good and I will be replacing both sending units. Now if I can fix the hot switch problem I will be close to cruising again! Many thanks, Steve
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| TomO | -- 07-28-2011 @ 7:21 AM |
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Are you sure that your car does not have halogen headlight bulbs or tail light bulbs. They are very high current devices and can cause your problem. To trouble shoot the light switch, use your voltmeter. Connect the POS lead of the meter to the NEG battery post. Then connect the COM lead of your meter to the input of the light switch. Turn on the lights and measure the voltage. It should be 1/10 of a volt or less. Turn off the lights and move the probe to the output of the switch and remeasure the voltage with the lights on. When the voltage increases, you will have found the source of the resistance. Depending on how your gauges are powered, you may need a 12 volt sending unit for the right side. The left side is just a high temperature switch and is not voltage sensitive. Tom
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| 49FH8 | -- 07-28-2011 @ 1:38 PM |
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Tom...I REALLY appreciate your help! I have 11+ volts at the input of the switch and therefore the same 11+ volts to the lights with switch on. 1/10v output with switch off. I assume I should not have 11+ volts on the input side. What now? Based on your instruction, the left sender is bad but planned to change both. How do I determine if the right sender is 12v. Thanks again for your help, Steve
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| TomO | -- 07-28-2011 @ 5:47 PM |
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Steve, I am sorry but I made an error in describing the meter lead hook up. I described it for a POS ground system and your is a NEG ground system. The COM lead of the meter should be on the POS terminal of the battery and you would probe with the POS lead of the meter. This will give you the voltage loss between the 2 points. A 12 volt sender is usually marked with 12 or 12V. I would not change the right sender if it is working. New parts are not always better than old working parts. Tom
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| 49FH8 | -- 07-31-2011 @ 4:23 PM |
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Tom, Finally getting time to do test today. If I am doing this correctly, the results are: Lights on - Input -.43 volts Head lights on - Head -.9v Dash -.94v Tail -.97v Park -12.34v Park lights on - Head -12.32v Dash -.68v Tail -.68v Park -.71v Let me know what this means to you. Thanks, Steve
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| TomO | -- 08-01-2011 @ 7:00 AM |
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Steve, You did the test correctly. You have a voltage loss of .43 volts on the input to the switch. You may have a loose or corroded connection in the wires leading to the switch. Your light switch has internal resistance that is causing you to loose almost 1 volt. It should be around .5 volts with a 12 volt system. You can try operating the switch many times to see if you can lower the voltage drop across the switch. If that doesn't work, I would disassemble the switch, clean the contacts and lube them with a corrosion inhibiting grease. Now that you know how to do the test, move your probe to the head light connector. This will give you the total voltage loss to the lights. Because the terminals are getting hot, you should show more voltage drop at the headlight connector. Tom
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| supereal | -- 08-01-2011 @ 9:51 AM |
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Sixteen to eighteen gauge wire is not sufficient to carry the load of even non-halogen headlights. Ordinary headlights draw a bit over 100 watts, and halogens about twice that.
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| 49FH8 | -- 08-02-2011 @ 6:17 PM |
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I appreciate the help. The weather has been so hot and I haven't checked anything else yet. I will confirm the wire size and check the switch...I need a garage with AC. Thanks, Steve
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| 49FH8 | -- 08-04-2011 @ 5:08 PM |
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I faired the heat and changed the left heat sender and no change with the temp gauge. Changed the left sender and still no change. I don't see a voltage reducer...can that be a problem. The temp gauge is most important right now. Thx, Steve
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| TomO | -- 08-05-2011 @ 7:29 AM |
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When you did the tests for the temp senders, what were the results? Did both senders fail the test? You should have a voltage reducer going to the gauges. I missed your reply about the wire size before. Supereal caught it. Your headlight wiring is too light for the amount of current that the bulbs draw. You should have a minimum of 14 gauge wire to the headlights and 12 gauge wire to the switch. Tom
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| 49FH8 | -- 08-06-2011 @ 4:37 AM |
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The best I could tell is the left sender failed the test however I did not remove the wire, but clipped on to it. Both went to cold. The right sender seemed to hang around hot before slowly going to cold. I will retest removing the wires as you originally instructed and see what happens. I will also try the grounding suggestion. I was told when I bought the car the temp gauge used to work...for whatever that's worth. I will try to trace the wires to be sure about not seeing a voltage reducer. Is there typically one for each gauge or one for all the gauges. I did see several under the dash but have not traced all of them. One of them that seemed to have some crusty white stuff around the edge but I was standing on my head on the floorboard and the heat got to me before I could trace the wires. Wire size - How do I determine wire size without a micrometer? I have experience with house wiring 12 and 14 gauge and estimated the size based on that. And some experience with wiring on a motorcycle, but purchased the wire in a specific gauge. It seems difficult to determine gauge since the insulation thickness would skew the observation method. Wouldn't the wire get hot if it was insufficient in size? It is the input terminal on the switch that gets hot first. I appreciate the help. Thanks, Steve
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| TomO | -- 08-06-2011 @ 7:10 AM |
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!2 volt conversions are custom conversions in that each guy decided how to do it. You may have one reducer for the cluster or one for each gauge. On the temp senders, because you jumpered around the left sender and the gauge went to cold, your right sender seems to be working correctly. If it indicates the wrong temperature, like always cold, it could be the that the wrong voltage is being supplied to it. If you have a volt meter, connect it to the wire from the gauge with the ignition on. If there is a reducer, the voltage will be neat 6 volts. If it is near 12 volts you will need a reducer. Your voltage readings indicate a large drop on the input of the light switch. You could make a temp connection from the battery to the input of the light switch with 12 gauge wire and then see if your terminals heat up. The easiest way to determine wire size is to purchase a wire stripper and crimp tool. They have the wire size next to the stripper hole. Strip a sample of the wire and look to see if all of the strands are there. If they are that is the size of your wire. Tom
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