Headlight suddenly don’t work

[Mertz]

Got the bed back on my truck and installed the tail light. I checked to see if I have tail lights with the headlight switch on and got no power to the wire and the headlights didn’t come on. Checked the fuse and it was blown so I replaced it and still no head lights or taillights. The turn signals work but they are on a different fuse. Also don’t seem to have power to the brake switch. The truck starts and the amp meter shows a charge. I hate electrical problems. Everything was working fine until the bed went on. The amp meter showed a pretty good charge when I reved the engine. Could I have blown the voltage regulator?

[Plymouthy Adams]

likely self inflicted wound, go carefully back over your work as you stated, was good before now bad after your maintenance action....look close for a pinched harness/wiring to the rear.....

[Mertz]

I checked the harness and it is away from the work I’m doing but I will check again. Something had to blow the fuse but the new one should have worked and the engine starts. 

[Veemoney]

Check the new fuse to see if it blew again, if so it would be a short somewhere. 

[Plymouthy Adams]

check you light housing and sockets also....they could have been pulled taunt a bit, cut the insulation, pulled a pin in the socket to lay against the housing.....do not overlook your license plate light in this.   

[Mertz]

Double checked the wiring and no damage from the bed work. I didn’t do anything with the front harness. I used a jumper to work the taillights and they work when I added a ground but they worked before without it. I jumped the brake light switch from the battery and added a ground jumper and they now work but still no power to the switch. Triple checked fuse one visual inspection and another with a test light. I started the truck and with few rpm was charging well over 35amps. There is a slight discharge showing on the meter when I turn on the lights. It is also slightly below neutral with nothing on but I don’t know if that is normal. 

[Dave72dt]

Wooden cross rails so the bed is insulated from the truck frame?  Add a ground from the metal box sides or tail lights to the frame.

[Mertz]

I will add the ground strap which I am currently using a jumper. 
 

I looked at the wiring diagram and power goes through the amp meter and back to the voltage regulator. The test light shows power to the B terminal. From the amp meter it goes to the horn and light switch and brake switch. No lights, no horn and no power to the brake switch. So I guess the power is stopping at the meter. I’ll check the wire coming out but it’s a pain getting under the dash. Or there is a problem at the fuse connection. 

[Mertz]

Took the test light under the dash. Power in and out of the amp meter. Power into the light switch and that’s where I got lost. One terminal on the back has power and the other doesn’t. Will have get a picture of the switch to see what’s what. 

[greg g]

Try cycling  the stomp switch for high beams.  Those have points style contacts that can carrode  through disuse.  Check there for proper connections.  It will have one power in and two outputs 1 for low, one for brights.  These will typically go forward to a terminal strip or block on thr radiator caresupport as individual wires, then split to feed the L/ R  bulb connection.  Typically you should check the head lamp grounds first as 6v needs clean grounds.  Good grounds well make your lights brighter in the deal.  Cuz a 40 watt element is a 40 watt element whether it's powered by 6v or 12v.  Ask Mr. ohm, if you need more convincing.   Also check to see if some one put skinny 12v wire in place of thicker 6v wires.  Ohm had something to say about having adequate cable to supply the currant to properly supply enough energy to put out full wattage.  Thank you Messers Ohm and Mr. Watt for their formulas insights thoughts.

 

Edited August 17 by greg g

[Plymouthy Adams]

this may sound a bit silly to some but did you check the fuse with the ohm meter, could be an open inside one of the end caps and not readily seen by the naked eye.....

[Mertz]

I checked the fuse with a test light directly at the battery yet everything points to a bad fuse. I have power to the fuse housing and the battery terminal on the switch but no power to the AUX terminal which should provide power to the horn and brake switch. Maybe a bad connection inside the fuse holder. I’m going to jump the 2 terminals and see what happens. 

[TodFitch]

4 hours ago, Plymouthy Adams said:

this may sound a bit silly to some but did you check the fuse with the ohm meter, could be an open inside one of the end caps and not readily seen by the naked eye.....

I have had this occur for me a couple of times on the glass tube Buss style fuses. Visual inspection showed it looked good but an ohm meter showed it bad. The solder on one of the end caps was bad and there was no connection between the end cap and the fusible link.

[B1B Keven]

2 hours ago, TodFitch said:

I have had this occur for me a couple of times on the glass tube Buss style fuses. Visual inspection showed it looked good but an ohm meter showed it bad. The solder on one of the end caps was bad and there was no connection between the end cap and the fusible link.

X's 2.

[Mertz]

I have tested the fuse several times both by ohm meter and test light. It is good. I jumped the battery terminal on the switch to the AUX terminal and I have both headlights and brake lights but no horn. I think the fuse might be making an adequate connection inside the switch. I’m going to spray electrical cleaner into the switch and see if that might solve the problem. 

[Mertz]

Spray cleaner didn’t work on the headlight switch but now the horn works. I was getting ready to put on a ground strap for the bed when I realized the running boards connect to the rear fenders and the bed but paint might have limited the connection. The rear fender brace also connects the frame to the bed. I cleaned off some paint from the brace, fender and frame and now I have a good ground. This off course has nothing to do with the lights. 

[MBF]

On these old vehicles I run redundant grounds.  Batt to engine, engine to frame, and frame to body.  I also fuse individual circuits instead of the original setup.  Don’t forget that the headlight switch has a circuit breaker mounted on it and that may be the culprit.

[Mertz]

I have a large ground cable to the engine and frame. By circuit breaker do you mean the fuse?  If not where is the breaker?  So far I believe that even though I have a good fuse the power is not getting to the AUX terminal. I’m going to add a 30amp fused jumper between the terminals.  Things worked when I used a jumper cable. I can’t find a replacement switch exactly like mine and pulling the wires from the switch will probably be very difficult. It was fine I wonder what changed. 

[Mertz]

I installed a fuse holder with a 20amp fuse (changing to 30amp when I find one) between the two terminals on the switch and now I have lights and brakes. Problem seems to be a disconnect at the switch end of the fuse holder. 

[Sniper]

Way to persevere and thanks for telling us the problem

[lostviking]

Take a look at this thread. I took mine apart and cleaned it up. You can see how the brass bar shorts the disks to make contacts. I'm betting you can clean it up, they look pretty beefy.

 

 

[Mertz]

I sprayed electrical cleaner in mine but it didn’t help. I have one lug that has come off. It is the one furthest to the top in the picture in the link. Does anyone know what that feeds? I assume it’s the running lights because everything else is working and I used the running lights for my turn signals so they are not connected to the switch anyway. Also I can’t get the connection loose. I’m afraid if I try to remove the wires on my switch I will break something. 

[Plymouthy Adams]

sounds like you already have broken something, maybe two somethings....check your wiring schematic against the color code and connection point to the switch, just saying a wire is loose is vague at best.  

[Mertz]

That terminal was already off when I got the truck. The wiring diagram I have doesn’t show the terminals as they actually are on the switch. It shows 4 and only three used. Pretty hard to tell the color after 84 years. The loose wire is, as I stated, the one at the top of the picture in the link that was posted in this thread. 

[lostviking]

Do you have the factory service manual? I bought mine from RockAuto. Mine shows all the terminals on the switch, so if your diagram doesn't, and it's not a factory manual, you might consider buying one. They are pretty cheap.

On 8/29/2024 at 3:48 PM, Mertz said:

I sprayed electrical cleaner in mine but it didn’t help. I have one lug that has come off. It is the one furthest to the top in the picture in the link. Does anyone know what that feeds? I assume it’s the running lights because everything else is working and I used the running lights for my turn signals so they are not connected to the switch anyway. Also I can’t get the connection loose. I’m afraid if I try to remove the wires on my switch I will break something. 

My switch was perfect on the inside, I figure your is probably also. The terminals on the outside however were very "used" looking. I doubt the problem with the switch is internal (but I'm married, so I've been wrong before). I'll assume that you are working on the 40 Plymouth, since you didn't say (or I missed it). Maybe post a picture of your switch. My manual doesn't show any switches with only four terminals. What is the exact model?