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Any suggestions, one headlight won't work 65 mustang

Clark65mustang

By Clark65mustang
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Clark65mustang

Clark65mustang

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Hello All,

 

I changed my headlight and it still doesn't work. I'm guessing I have an electrical issue. What should be my next step? I do not have any sort of tester, but I will pick one up depending on y'alls advice. Could it be the headlight switch? I tried the low and high beam and neither worked. The driver side headlight works fine and I check the actual light on the good side and it does work so it must be something with the connection? Thanks!

 

-Clark

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Rusty_OToole 25,000+ Points

Rusty_OToole

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First check if the headlight is getting power. A test light or multimeter is good for this. If it is, you most likely have a faulty ground. If no power is getting to the plug lift the hood and trace the wiring back. At some point the left and right headlights are connected, you know you are getting power to that point because the other side works. I would put my money on a badly corroded plug or a bad ground but could also be 2 broken wires.

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Clark65mustang

Clark65mustang

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Thanks Rusty, I appreciate your time! I'll stop by autozone on my way home from work and get a multimeter. I haven't used one of these before but from some quick google research it seems like I remove the headlight and put the prongs into the headlight plug. For checking the ground, would I need to remove the headlight assembly and trace the ground wire all the back looking for a break? Thanks again.

 

-Clark

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trini 5,000+ Points

trini

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Your light switch connections may be loose or frozen. Best way is to check the wires at the terminals. One at a time. Move the switch from park to  high to low . It is possible the switch terminals are loose. If there is a dip  switch for high and low , check that out too. You may use a common test light for the job. It would be nice if if you can get a wiring diagram. It will show you if there is a light relay. Another way is to use jumper from  battery  and inject wires individually at terminals at switch.  

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Clark65mustang

Clark65mustang

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Thanks Trini, I'm not really following your comment about the "dip switch for high and low."  Where would I check the wires at the terminals? Would that involve following the headlights wires from the plug to where ever it connects? Thanks. this is my first time dealing with an electrical issue.

 

-Clark

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rocketraider 25,000+ Points

rocketraider

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Dimmer switch which you've already tested.

 

While you're at the parts store get a can of electrical contact cleaner. That and some fine sandpaper can help clean terminals inside the plastic plugs.

 

What you're describing does sound like a ground issue since neither filament will light.

 

A factory style wiring diagram is a good investment. The way Ford did theirs, wiring diagrams for all series came in one manual and I'm told complete ones can get pricey. Surely, as popular as 1st gen Mustang is, someone has published the Mustang chart separately.

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Rusty_OToole 25,000+ Points

Rusty_OToole

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6 hours ago, Clark65mustang said:

Thanks Rusty, I appreciate your time! I'll stop by autozone on my way home from work and get a multimeter. I haven't used one of these before but from some quick google research it seems like I remove the headlight and put the prongs into the headlight plug. For checking the ground, would I need to remove the headlight assembly and trace the ground wire all the back looking for a break? Thanks again.

 

-Clark

The plug has 2 power wires (hi and lo beam) and a ground wire. Unplug the bulb, stick the positive probe of the meter in one side, ground the other probe to a bare metal spot on the body  and turn on the lights. See how many volts you have. Check the battery first, you should have practically the same voltage at the socket.  If the battery reads 12 volts and the socket only 10, you have a bad connection somewhere.If you get nothing there is your problem. Check both sides to see if you have power. To check the ground, switch to resistance or ohms and do the same, there should be practically no resistance from the ground terminal to the body.

You don't necessarily have to remove the light, often you can get at the back of the light from under the hood and unplug it. Trace the wires back and if you see any that are broken, frayed or corroded that may be the problem.

Edited by Rusty_OToole (see edit history)
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Frank DuVal 10,000+ Points

Frank DuVal

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9 hours ago, trini said:

Your light switch connections may be loose or frozen.

Only one headlamp has issues so it is not the light switch on the dash.

 

I agree on ground, but usually this makes the headlamp dim instead of out, since it does get a ground through the other headlamp. You know, 12 volts through the filament that is supposed to light, since no ground, back through the other filament to the other headlamp's filament that is not currently connected to 12 volts (the other filament is connected to 12 volts) and to ground. So very dim, as the 12 volts is going through three filaments to get to ground.

 

So if the headlamp is very dim, then clean the ground connection.

Edited by Frank DuVal (see edit history)
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m-mman 10,000+ Points

m-mman

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On 9/4/2021 at 6:16 PM, Larry Schramm said:

My bet is on a bad ground.

As rusty describes there are 3 prongs on the bulb and 3 prongs on the plug. 2 prongs give power (one high and one low beam) and the other is a little wire that ends in a ring type connector that is attached to the inner fender with a self taping screw.  (a sheet metal screw)  Trace this wire back through the fender to the under hood area. 

 

Guaranteed, the little screw is loose and/or it has a little rust or corrosion between the connector and the fender. Undo the screw then use sandpaper to clean the connector and the fender where it attaches. You want to see shiny metal. Reattach everything and you should have no problems. 

Notes:

1. On a 65 Mustang you will need to remove the headlight ring and bulb to get to the plug. 

2. As long as you have cleaned one ground wire, clean the other. It has been exposed to the same conditions for the same length of time. 

3. it is possible that the bulb is burned out completely, but typically there is one filament still working. 

Edited by m-mman (see edit history)
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pfloro 1,000+ Points

pfloro

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A wiring diagram is worth a thousand words...!

 

As you can see, the '65 Mustang electrical system is not complicated. As others have said, based on your trouble, the ground connection on the dark headlight is probably not making contact to the unibody. The ground wire jacket is solid black.

 

Please keep us posted.

 

Paul

 

 

1965e.jpg

Edited by pfloro (see edit history)
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JACK M 25,000+ Points

JACK M

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Try another head light, You can do this while its hanging by its wires.

Since you are not experiencing a dim light it would suggest that both beams are burned out.

Swap sides if you don't have a spare bulb. If your problem goes to the other side well,,,, duh...

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TerryB 25,000+ Points

TerryB

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6 hours ago, JACK M said:

Try another head light, You can do this while its hanging by its wires.

Since you are not experiencing a dim light it would suggest that both beams are burned out.

Swap sides if you don't have a spare bulb. If your problem goes to the other side well,,,, duh...

He said both headlights work on the drivers side so my money is on electrical harness, especially the ground connections.

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Frank DuVal 10,000+ Points

Frank DuVal

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Both headlamps? The is one 7" sealed beam headlamp per side on a 65 Mustang.😉

 

Clark never answered if the passenger side is very dim or completely out. He did say he changed the headlamp and it does not work. I wonder if the original problem was both beams (filaments) out or just one and now both are out.

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TerryB 25,000+ Points

TerryB

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11 hours ago, Frank DuVal said:

Both headlamps? The is one 7" sealed beam headlamp per side on a 65 Mustang.😉

 

Clark never answered if the passenger side is very dim or completely out. He did say he changed the headlamp and it does not work. I wonder if the original problem was both beams (filaments) out or just one and now both are out.

Frank, he tested both of his cars headlights in the side that was working and both worked.  That proved both of the headlights were in working order.   

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trini 5,000+ Points

trini

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To check to see if the headlight is not burnt out get a 3 wire pigtail , pull the existing one out and plug the pigtail  in. Use a jumper from the battery and inject directly. It is not surprising to find lots of green corrosion in terminals.   

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Frank DuVal 10,000+ Points

Frank DuVal

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3 hours ago, TerryB said:

Frank, he tested both of his cars headlights in the side that was working and both worked.  That proved both of the headlights were in working order.

OK, got it. Yes, he said that. I just read your comment oddly. Of course!😄

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TerryB 25,000+ Points

TerryB

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1 minute ago, Frank DuVal said:

OK, got it. Yes, he said that. I just read your comment oddly. Of course!😄

I used to write instructions for factory maintenance people so I’m used to seeing different takes on what I thought I wrote😀. With both beams not working my first impression is a bad ground on that side or a very poor condition headlight plug.
 

Hope you are having a good day Frank, I always enjoy your inputs.  Also hope the guy that started the post finds his problem too!

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Clark65mustang

Clark65mustang

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So I don’t think it’s the ground… I found a screw with a black wire behind my battery. Very rusty. Hard to see in the photo. I cleaned it and still nothing. I bought a cheap multimeter and it doesn’t seem like the tongs are long enough to test the headlight socket. Should I just keep taking apart these headlight parts?

A85F3820-9587-43EF-9847-3ADD0954C6D4.jpeg

 

249154C0-BD77-4E23-9C65-D6F343677795.jpeg

Edited by Clark65mustang (see edit history)
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Frank DuVal 10,000+ Points

Frank DuVal

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Left side of car is driver's side in the US. That's why they are called left hand drive cars.😉

 

Right side of car is passenger side in the US.

 

Clark, can you see what caused the damage to the wires? Around here it is rodents. But maybe it is a sharp edge without protection?

 

In general twist and tape is not a good repair. This might need a soldered in new piece of wire (three of them), as they may be too short to repair without increasing length. Can you solder?

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Frank DuVal 10,000+ Points

Frank DuVal

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Nothing quite more fun than driving at night at speed and having no headlamps suddenly!  BTDT in my  old 50 Champion back in college. 😅

 

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pfloro 1,000+ Points

pfloro

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The connector and wire insulation in your photo looks pretty banged up. Why chance a potential fire...

 

As was mentioned, reproduction wire harnesses for all sections of early Mustang electrical systems are readily available. The USA made harnesses are not cheap because cheap died years ago.

 

Scott Drake products are well engineered and manufactured...

 

Paul

 

This harness is for the '65 Mustang with instrument cluster oil pressure & ammeter gauges (they came with the GT package).

https://www.jegs.com/webapp/wcs/stores/servlet/SearchResultsPageCmd?q=1965+mustang+headlight+wiring+harness&storeId=10001&catalogId=10002&langId=-1

 

This harness is for the '65 without the above 2 gauges. This was the standard Falcon instrument panel.

https://www.jegs.com/webapp/wcs/stores/servlet/SearchResultsPageCmd?q=1965+mustang+headlight+wiring+harness&storeId=10001&catalogId=10002&langId=-1

 

 

 

Edited by pfloro (see edit history)
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pfloro 1,000+ Points

pfloro

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This is not a difficult task. I replaced this same harness on our '66 Mustang GT years ago. 

 

The USA made harnesses are exactly the same as the original. By taking good pictures of each connection point before you begin, working from the firewall connector toward the outlying connectors, and "laying in" the new harness as you remove the old one, it's an easy and rewarding task. 

 

Use care when disconnecting the old harness so as not to damage the connectors you'll be tying into with the new. Remember, that old plastic is brittle...!

 

I would use fine emory cloth to remove any oxidation from the old connection points (both male & female). Clean up the firewall connector terminals too...! Do it once, do it right...

 

You will want to buy new plastic "straps" which secure the harness to the engine compartment along it's way to the end points. Cut the old brittle straps and replace with new ones...

 

Underhood Strap Kit:

 

https://www.cjponyparts.com/cj-classics-wiring-harness-retainer-kit-21-piece-kit-1965-1966/p/HW918/?year=1966&gclid=Cj0KCQjw1ouKBhC5ARIsAHXNMI-1JXhbMKVPmidO5H5wWJKA2532puU8J2hZgo3UZ_kvA0zsO0J5RAYaAmmpEALw_wcB

 

You are fortunate to be working on a 1st generation Mustang. High quality reproduction parts are readily available at modest prices. However, some of the imported stuff is junk. 

 

It's an easy car to get into tip-top shape...!

 

Paul

Edited by pfloro (see edit history)
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Rusty_OToole 25,000+ Points

Rusty_OToole

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We are talking about 3 wires, one about a foot long the others no more than 3 or 4 feet long. If you have never done this before it should still take less than an hour, if you know how to solder wires. The secret is, the wire must be bare and clean, with flux on it, and it needs to be good and hot so the solder flows into the joint. If you have not done this before you may need help with the soldering, but stringing a couple of wires and a new plug should not challenge anybody.

 

Or you could take some scrap wire and practice soldering the ends together until you get the hang of it. Don't forget to slide the heat shrink tubing on BEFORE you connect the wires.

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Frank DuVal 10,000+ Points

Frank DuVal

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On 9/16/2021 at 1:01 PM, Rusty_OToole said:

Or you could take some scrap wire and practice soldering the ends together until you get the hang of it. Don't forget to slide the heat shrink tubing on BEFORE you connect the wires.

Practice is the only good way to learn soldering. Read, watch you tube or whatever, but iron (or gun) in the hand and keep soldering things together for practice.

 

Wire needs to be shiny (copper color or tinned color, typical only ever saw copper color on automobiles), no black or dark copper tarnish.

 

Yes, heat shrink, connector backshells, etc. need to be on before last connection on a piece of wire/cable is made. VERY frustrating if forgotten!🤬

 

I typically use the rosin core solder that applies the flux as I  solder. If extra flux is needed, buy electronic type flux, not the plumbing type flux, that does/used to contain "acid". 

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