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EFV-8 Club Forum / 1940 Ford Discussion / Dim instrument panel lights

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Posted By Discussion Topic: Dim instrument panel lights -- page: 1 2     Carcheologist 04-22-2022 @ 1:53 PM reply profile send p.m. New Member Posts: 132 Joined: Jan 2016 TomO, Great explanation - now I understand your previous post. Thanks for clarifying. TomO 04-22-2022 @ 7:58 AM reply profile send p.m. Senior Posts: 7250 Joined: Oct 2009 To perform the voltage drop test you use the DC volt setting on your meter. The readings are low because you are measuring the difference in voltage from the source to the destination. The actual voltage at the bulb would be battery voltage minus any loss due to circuit resistance. If you battery was at 6 volts and you had 0.5V drop, the voltage at the bulb would be 5.5 volts. Typically each switch in a 6 Volt system has about .012 ohms resistance. Trying to measure this amount with an ohm meter requires special equipment. Using a voltmeter to measure the difference between the source and the bulb gives us the resistance in the circuit and makes it easier to determine the point of the resistance. The headlight bulbs draw about 8 amps of current so when you know the voltage drop in a circuit, you can use an ohms law calculator to determine the resistance in the circuit. Tom RAK402 04-21-2022 @ 5:17 PM reply profile send p.m. Member Posts: 436 Joined: Jul 2015 I agree-not a fun job. I am getting ready to take mine out for the second time in a year. This time it is to get the dashboard painted with the correct colors. Carcheologist 04-21-2022 @ 7:11 AM reply profile send p.m. New Member Posts: 132 Joined: Jan 2016 RAK402, My battery gauge shows to be working fine too; now comes the unpleasant chore of getting behind the instrument panel to check the light bulbs - it's a real pain with it in the car. RAK402 04-20-2022 @ 9:22 PM reply profile send p.m. Member Posts: 436 Joined: Jul 2015 Carcheologist, You are right, the battery gauge is a voltmeter. I started to suspect something was wrong (and had been wrong for a long time), but what really cinched it was when I put the alternator in. The gauge still read very low (well below the green area). I put a voltmeter on the battery and it read around 7 volts. I found an NOS voltmeter and tested it-it showed the voltage at the top of the green. I swapped it out and now it reads at the top of the green. It seemed weird to have it fail, but then again, it was over 80 years old. If I recall correctly, the 1939 Deluxe and the 1940 Deluxe and Standard are the only early Fords with Battery Gauges. The earlier ones (and the 1939 Standard) all had ammeters, as did the rest from 1941 on. I hid an ammeter on mine, so I can see the battery voltage with the normal gauge, and see how the charging system is behaving (real time) with the ammeter. My car is all apart right now, but when I put it back together I am going to follow TomO's advice about the dim headlights. Mine aren't too bad, but I think they should be brighter. Putting it back together will allow me to go through all the electrical connections, clean them, and test things. Carcheologist 04-20-2022 @ 10:42 AM reply profile send p.m. New Member Posts: 132 Joined: Jan 2016 TomO, Thanks for your in-depth troubleshooting instructions. Please forgive me, I'm somewhat "electrically challenged" sometimes. Do I set the test meter on Volts or Ohms? And, am I correct in understanding you are speaking of only a fraction of a volt (0.4 volts), etc. when measuring with the test meter? I thought I would expect to see higher voltage at the headlamp socket. Sorry if I'm a little slow and appreciate your clarification. bo8109b 04-20-2022 @ 9:48 AM reply profile send p.m. New Member Posts: 179 Joined: Nov 2009 Years ago, I changed my '40 instrument bulbs to 6V LED bulbs which really brightend things up. May still be available on Amazon. TomO 04-20-2022 @ 7:38 AM reply profile send p.m. Senior Posts: 7250 Joined: Oct 2009 The dimmer switch is the first place that I look when troubleshooting dim lights. The sealed beams need at least 6.0V at the bulb to reach a normal brightness. The way that I troubleshoot dim headlights is use a voltage drop test to find the points of resistance. Connect the black or COM lead of yoiur meter to the NEG post of the battery and the red or + lead to the headlight socket wire for the right hand headlight. Turn on the head lights. The meter should read 0.5V or less. Turn off the lights. If it is more than 0.4V move the red lead to the dimmer switch terminal for the low beams and turn the lights on. The reading should be less than 0.3V. If the reading is higher move the red lead to the input to the dimmer switch. the reading should now be 0.2V or less. Continue this process back to the input of the light switch where the meter reading should be less than 0.1V If the reading is less than 0.4V, move the red lead to the POS post of the battery and the black lead to the grounding wire on the headlight plug. Turn on the lights. The reading should be 0.1V or less. If it is higher check your grounding straps for corrosion or replace them. The stock dash light bulbs are no.51 bulbs, you can replace them with no. 55 bulbs. RAK402 has the right idea about having a clean glass over the instruments and having a good reflective surface for the light to direct the light. Tom Carcheologist 04-20-2022 @ 7:05 AM reply profile send p.m. New Member Posts: 132 Joined: Jan 2016 1931Flamingo, Yes, I did check the ground connections for the headlights and they seem to be fine. A while back, I installed a new headlight switch and added a relay. I'll check everything again to make sure. Seems like I read somewhere that an old, worn foot dimmer switch can cause dim headlights too. Know anything about that? 1931 Flamingo 04-20-2022 @ 6:54 AM reply profile send p.m. Member Posts: 386 Joined: Nov 2019 For headlights, make sure you have good grounds or add another. You could change the bulb size for the dash. Paul in CT

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