Dim Headlights on 40:

[joe 1950]

doesn’t matter if it’s cable or braided strap but get it big enough mine goes from the bell housing to the body not the frame body is mounted on rubber mounts

[JSeery]

Originally Posted by 1931 flamingo

"not reading in the green going down the road about 60mph."


What's the fix for this ?? I also have this problem. Gen and regulator have been gone through.
Paul in CT

You would first have to determine if it is the Generator/Regulator output or the gauge that is the issue. Sounds like you have checked the Gen/Reg, so most likely it is the gauge. Is the wiring to the gauge and the gauge ground in good shape? I would take a voltage reading at the gauge and see what you get, should be somewhere a little above 7 voltage with the engine rpms up. (this all assumes were are talking a voltage meter and not an ampmeter here)

[JSeery]

Originally Posted by 40ford

I think I will just get another cable and run it from maybe a hog head bolt to the frame under car. I don't think this would hurt and it may help? Would it matter if it was just a cable or should it be a woven ground strap?

I'm a big believer in grounds and they are often the problem with electrical issues. But the results you are posting appear to be more than a grounding problem (it is also possible and common to have more than one electrical issue). You really need to troubleshoot this and determine what the issue(s) is/are.

Get a fairly heavy gauge, long wire and connect it to the ground on the battery. Now recheck your voltage reading into and out of the light control switch (and other devices, such as the dimmer switch, input to headlights, etc). The voltage at any of your check points should be very close to battery voltage, in other words, there should not be much voltage drop in the wiring or any devices such as the light switch. The voltage from the battery should be >6 volts not running and >7 volts running (above idle).

Between using a dedicated ground directly to the battery for voltage checks and jumper wires to bypass suspect areas you should be able the isolate issues in short order. Additional grounds are always a good thing, but you still need to isolate any issues and resolve them.

[Aarongriffey]

The ground cables can be a woven ground strap. Or a regular insulated cable. Doesn’t matter.
Six volt systems need at least a size 1 for both battery cables. I like to use larger.
Put a ground strap or cable from the frame to the engine or transmission might give the starter some extra pep. Sure wouldn’t hurt but I doubt that is the dim light proble.

[40ford]

I was real curious and checked the charging voltage on my truck today.It is a stock 1952 F-1 with everything pretty much new including the wiring harness.With the truck at high rpm I am getting 7.50 at the battery.Should a 40 do the same thing.The lights on my truck are just about as good as if they were 12 volt!

[aussie merc]

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your on track you also need to check what is called stored voltage that is what is avalible at the battery after it has sat isolated for 24 hours a battery in good nick will only drop about a half volt and then stablise so if you charge at 7,5 have 7 after stopping eng it should stabilse at around 6.5 volts this also will tell you if you have any standing current draws ie clock, boot or bonnet lights that are remaining on etc a battery thats not quite right will give many false signals before failing any dought have someone loadtest it

[TomO]

A voltage drop test measures the resistance in a circuit and is more accurate way than using an ohm meter or measuring the voltage at the end point of the circuit. An ohm meter is hard to read when the circuit resistance is less than .05 ohms, but a voltage drop test will show how much voltage drop wcan occur with .005 ohms.


A voltage drop test is done by connecting a volt meter between the source of the voltage (battery) and the end point of a circuit while the circuit is in use (lights on or starter engaged).


To test the headlight circuit on an 6 volt pos ground car, you would connect the COM lead of the volt meter to the NEG battery post and the + lead to the connector closest to the last point in the circuit. On a Ford, it would be the bullet connector by the right headlight, using a paper clip or other thin wire to probe inside the bullet connector. The total loss should be less than 0.5 volts . To isolate the source of n\the excess resistance, you would move the red probe back one connection at a time. Each bullet connector should not drop more than 0.05V. The circuit breaker, dimmer switch and the headlight switch should not drop more than 0.1V each.


To test the grounding circuit for the headlights, connect the COM lead of the voltmeter to the grounding pigtail in the light bucket and the POS lead of the meter to the POS battery post. With the lights on, the reading should be less than 0.1V.


If you need more help, I check the Early Ford V-8 Club Forum regularly.

[40ford]

Tom,I just don't understand what is going on.I checked my voltage on the hot wire going into headlight switch this morning with car not running and sat all night and I get 6.28 volts and I check the voltage going out to headights and I get 5.51 volt?I jumped over the switch and the jumper wire clips got real hot fast sending out 6 volts to headlights?Like I said before this is a new switch.

[Ken/Alabama]

There is a large wiring connector located close to the headlight switch. I found that connector getting hot and was the cause of my poor lightning issues. Finally removed the connector and crimped and soldered the wires together. No more getting hot and good lights.

[40ford]

Ken,I don't exactly know what wire you are talking about.Is it close to the instrument panel or part of the wiring harness?

[TomO]

Your post says that you have approximately 0.8V drop in voltage across your light switch. If you did the measurements correctly, your light switch is bad. The max drop across the light switch is 0.1V.


If it is a new switch, send it back to the vendor and request a replacement. If it is an original switch, you can try operating it many times and then recheck it. This operation will clean the contacts if they are the cause of the problem. The original switches can be disassembled and repaired.


I suggest that you do a voltage drop test as I described in my previous post. It is a much more accurate test than trying to read the voltage like you are doing. It will also help isolate the problem to the connection or component that is making your lights dim.



I have no idea why your jumper wire clips got hot, unless you were using 18ga jumper wire. You need a 12ga jumper wire to test the headlight circuit.

[1940 Convert]

If you aren't familiar with doing a voltage drop test there are several videos on Youtube. Like Tom says that is probably the quickest/easiest way to narrow it down if you can't get results with using a set of jumper cables to give temporary connections. I've often had luck with just giving a new temporary ground to body or chassis with a full size set of jumper cables.


That kind of weird that it shows this as my first post but still has my private messages and join date. I haven't logged in in quite a while.

[40ford]

Tom this is what I am using.I still have the old I think original switch.To me it looks like it has to be the switch because I am not getting 6 volt to dimmer switch?
12066761_dcd_85654_pri_larg.jpg

[JSeery]

Your jumps look like they are too light a gauge size for headlights. But that may be irrelevant at this point as it appears your switch is bad. If you want to bypass the switch while you are waiting on a new one, fabricate a short jumper of heavier gauge wire.

[40ford]

Originally Posted by TomO

Your post says that you have approximately 0.8V drop in voltage across your light switch. If you did the measurements correctly, your light switch is bad. The max drop across the light switch is 0.1V.


If it is a new switch, send it back to the vendor and request a replacement. If it is an original switch, you can try operating it many times and then recheck it. This operation will clean the contacts if they are the cause of the problem. The original switches can be disassembled and repaired.


I suggest that you do a voltage drop test as I described in my previous post. It is a much more accurate test than trying to read the voltage like you are doing. It will also help isolate the problem to the connection or component that is making your lights dim.



I have no idea why your jumper wire clips got hot, unless you were using 18ga jumper wire. You need a 12ga jumper wire to test the headlight circuit.

Is there a way to tell if switch is original?How do you clean the switch?The switch kinda looks like it has been taken apart before because of markings on tabs!

[aussie merc]

new or otherwise that switch is no good and has bad contacts and at best should only be used to run a relay otherwise needs to be replaced Bad contacts cause heat too much heat dosent end well

[40ford]

I called Carpenters this morning and told them the switch I had was defective.They are sending me another one no questions asked!Great service there!

[40ford]

I changed all my battery cables to size 00.Ran extra grounds from motor to frame and body.Car certainly cranks much faster.I hope this new switch cures my problem.I also ran extra ground wires at headlight buckets.I used this ground strap that Advance Auto sells which works real good for this.
5701635_rnb_60213_pri_larg.jpg

[1940 Convert]

I had some ground problems on my 40 also. Too much paint under the ground strap was keeping it from making good contact. Those universal ones make good supplemental grounds and don't look out of place.

[JSeery]

Originally Posted by 40ford

I changed all my battery cables to size 00.Ran extra grounds from motor to frame and body.Car certainly cranks much faster.I hope this new switch cures my problem.I also ran extra ground wires at headlight buckets.I used this ground strap that Advance Auto sells which works real good for this.
Attachment 438825

Be sure the metal is bare and clean under the ground straps. I put a little grease on both surfaces to help with rust and help with conductivity. I am not a fan of di-electric grease for this application, but that is just me, many use it. Di-electric grease is specifically designed to block current flow. With tight connections there is enough metal to metal direct contact that this is not much of an issue, but just doesn't seem like the right way to go to me. I use an electric contact grease that is designed to promote current flow, but it is more difficult to find. For a ground connection normal grease will work. Di-electric grease is designed to protect multi-pin connectors in wiring harnesses and needs to block current flow between pins located close to each other. Good stuff for the designed application.