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bluebus86
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Joined: September 02, 2010
Posts: 11075
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 Posted: Wed Oct 07, 2015 4:43 pm Post subject: |
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| rcroane wrote: |
Thanks for the replies.
I've been checking ground connections with my multimeter.
Just to confirm, is a reading of 0.1 ohms acceptable? How about 0.2 ohms?
Thanks. |
don't bother reading ohms, instead read voltage drop across each connection. Voltage drop is what your concerned with. the ohms is not relevant to the drop in voltage unless the current is known. .1 ohm is not much voltage drop for low current, but more for high current.
using voltage drop will tell you what percentage of voltage loss is at each connection measured.
so turn on the lights and probe for voltage across each connection for best results.
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rcroane 
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Joined: January 03, 2013
Posts: 2000
Location: Springfield, Virginia
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| Posted: Wed Oct 07, 2015 4:59 pm Post subject: |
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For example, if I put one probe on terminal 56 of my headlight switch and the other on terminal 56 of the dimmer switch, that will tell me if I have a voltage drop at the dimmer switch?
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bluebus86
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| Posted: Wed Oct 07, 2015 5:25 pm Post subject: |
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| rcroane wrote: |
| For example, if I put one probe on terminal 56 of my headlight switch and the other on terminal 56 of the dimmer switch, that will tell me if I have a voltage drop at the dimmer switch? |
I don't have the terminal number down. but if you probe the input of the dimmer switch across to the output of the dimmer switch, with the correct lights on (hi or lo beam) that will tell you the drop across the dimmer switch
If you want to find the drop from the ground screw at the light, probe the fender next to the screw and probe the light ground wire near the screw. that will tell you the drop of the ground connection between the two probes..
do likewise at the headlight switch, probe the input wire at the switch (the wire from battery) and probe the output wire at that switch wire that goes to lights via dimmer) and that will tell you the drop your getting across the switch (lights must be on for test)
you can then determine which connections are the worst and effect repairs. If your dropping two volts at the switch in a six volt car, that means you need to fix the switch, either bad internal contacts, or the switch connections are causing it. half volt drop in the switch might be considered normal, any more and your lights get really dim.
all the drops at each connection will add up to the total drop at the bulb.
lets say you only got 4.5 volts at the bulb,(6 volt system) if the ground is .25 volt drop, the dimmer .25 volt and the switch 1 volt drop, you can bring the light up to 4.75 volts by making the ground connection perfect (in theory not possible, but you can make it near zero drop) If you can clean up the switch contacts to only drop .25 volts, now you are at 5.5 volts, clean up the dimmer to give a .1 volt drop and now the bulb will see 5.6 volts, which is not too bad. don't forget to probe the drop across the fuses.
often there are drops at the fuses cause of dirty contacts and loose spring clips, and dirty connections at the wires. simply probe the fuse panel with the accessories on, probe each side of the fuse holder clips, and even probe the wire at in the trunk to the fuse clip, that will tell you where you need to clean or retension spring clips , or the wire to terminal connections.
you want to clean things up so that the individual drops are as small as possible.
you may find the biggest drops in the switches, and they can be hard to clean up, remove rivets or staked over metal to open the switch, and clean the contacts, regrease with dielectric grease and your switch can be like new again, or buy a new one. the switches are hard to fix as they are not designed for easy disassembly or reassembly, but often improvement s can be made.
do a complete assay of the circuit for drops at each connection, write the drops down on a copy of the wire diagram at each location, then work on fixing the easy to fix drops first, often low hanging fruit (easy to fix) drops are at the fuse box and ground points. clean the wire connections at all the swiches that have big drops and see how that improves things.
you only have 6 volts to start with, so each drop can add up fast to the level of lights not working anymore.
the drop across the light bulb should ideally be battery voltage, but it never is ideal. the difference in battery voltage to the drop across the bulb is equal to the sum of all the other drops form wires connections and switches.
if you find 5 volts across the bulb, then you know you have a total of 1 volt drop in the system, a .2 volt drop here, .4 volt there, .3 there, and .1 volt there. it all adds up in the end to the total drop at the bulb.
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rcroane
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Location: Springfield, Virginia
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| Posted: Wed Oct 07, 2015 6:02 pm Post subject: |
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Bluebus....once again, thanks for taking the time to write a great explanation. I did a few measurements and I'm getting drops in the 0.1 to 0.2 range. In one case, I got a negative .08 reading....what does the negative mean?
Could you also explain what you mean by "drop across the light bulb". How do I measure that?
Thanks.
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bluebus86
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| Posted: Wed Oct 07, 2015 6:42 pm Post subject: |
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| rcroane wrote: |
Bluebus....once again, thanks for taking the time to write a great explanation. I did a few measurements and I'm getting drops in the 0.1 to 0.2 range. In one case, I got a negative .08 reading....what does the negative mean?
Could you also explain what you mean by "drop across the light bulb". How do I measure that?
Thanks. |
negative values mean that you got the probes reversed, and that tell me your using a new fangled digital meter. the old analog gages never took kindly to reverse polarity, you could fry the meter pegging backwards.
now worries, just reverse the probes.
the drop at the bulb is the voltage across the bulb, so probe the bulb holder (as probing the bulb itself when in the bulb socket is not possible, unless you can actually touch the bulb contacts) Probe the ground and hot parts of the holder to figure out how much voltage is dropped across the bulb (and holder) of course besure to clean the bulb holder and tension the spring for best contact to the bulb
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61SNRF
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Joined: March 29, 2009
Posts: 4657
Location: Whittier 90602
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| Posted: Wed Oct 07, 2015 7:02 pm Post subject: |
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| Eric&Barb wrote: |
| ... When doing tests for voltage drops helps to have a draw on that wire to have the voltage drop show up. A couple of turn signal lights in parallel connected to the black wire normally going to the coil will do the trick. |
Good tip, optimally you want the worst case maximum load of current going through that one circuit all at once to measure the ultimate voltage drop.
Again, put one lead* of your DVOM on the +30 side of the ignition switch and the other lead on the +15 side. Switch it on and turn as many things on at once as you can to put the circuit under max load.
You want to see <0.2 volts on your meter, which is the direct measurement of voltage drop.
*I always forget but think it's Black (-) lead to +30 and Red (+) to load, because with a digital volt meter, it doesn't really matter which way you hook up the Red(+) or Black leads (-), even if your readings are shown in the negative the basic figure is still accurate. Correct your readings regarding polarity if desired by simply switching the leads.
If a person were not adverse to the idea, adding an Ignition switch +15 triggered power relay to the system could eliminate a whole bunch of voltage drop in an old original ignition switch operating on 6 volts. Of course the wiring is not going to be original anymore, but you would have a much more reliable and stable +15 power supply to draw from, and all of the workings could easily be hidden behind the dash cover as well.
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rcroane
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Location: Springfield, Virginia
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| Posted: Wed Oct 07, 2015 7:08 pm Post subject: |
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Only getting 4.8v when measuring across the brown wire and yellow wire at the bulb holder. Guess I better get back to cleaning. Biggest drop I found so far is between voltage regulator and headlight switch (.29v). Haven't tested battery to starter solenoid and solenoid to VR.
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bluebus86
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| Posted: Wed Oct 07, 2015 7:15 pm Post subject: |
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| rcroane wrote: |
| Only getting 4.8v when measuring across the brown wire and yellow wire at the bulb holder. Guess I better get back to cleaning. Biggest drop I found so far is between voltage regulator and headlight switch (.29v). Haven't tested battery to starter solenoid and solenoid to VR. |
ok .29 volt drop for that long run of wire from generator to the headlamp switch is not too bad. you still have nearly one volt drop over all however excluding the .29 drop from the regulator to switch. check the fuses, concentrate on the fuse for the light, then the drop across the switch itself and so forth. you got one volt missing between the bulb and the switch input. it is there some place
goodluck
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rcroane
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Posts: 2000
Location: Springfield, Virginia
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| Posted: Mon Oct 12, 2015 3:39 pm Post subject: |
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Spent some more time cleaning all the connections in the headlight circuit. The total drop from voltage regulator to headlight plug is .851v. This includes a drop of .282v from the VR to the headlight switch. The other drops range from .094v to .143v. Sure wish I could get the drop from the VR to headlight switch down further, but overall I'm happy with the result.
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