• Hello there guest and Welcome to The #1 Classic Mustang forum!
    To gain full access you must Register. Registration is free and it takes only a few moments to complete.
    Already a member? Login here then!

'66 Tail light troubleshooting

stump

stump

Member
After a drive last weekend I noticed the left tail/brake light on the Fastback wasn't working. This car has all new wiring, and the tail light plug is solid wiring (not the removable pig tail like my coupe). While checking for a loose connection I determined the problem was inside the plug. As I had the original pigtails from the coupe I decided to cut off the plug, add connectors, and use it. It's worked perfect all week. Meanwhile, I ordered a new set, which I used to replace the one from the coupe.

Well yesterday I replaced the pigtail and below are the results. As you know, with only two color coded wires, it's really hard to get the connections wrong... Also, I've only replaced the left side.

1. While applying the brake the instrument lights come on.
2. When the lights are on both brake lights are illuminated.
3. Brake lights work unless lights are on.
4. With the left pigtail disconnected the right works fine.

I replaced the new pigtail with the old one again, and everything's fine. No doubt something is going on inside the new pigtail; any suggestions on what it is, or how I can troubleshoot?

Thanks,
Gary
 
Replace the bulb .Maybe it has internal a connection or shortcircuit. :confu :confu
It can't be that hard to find but a bulb is the last thing men is thinking about. :bowdown
 
It kinda sounds like the wire codes may be backwards or wires crossed in the new pigtail. You 1-3 results sound like the brakes are activating the parking light s in the dash. Bet the front park lights were on too. Also, item 3....are you 100% positive the brake filament was lit and it was not the tail light filament you were mistaking for the brake lights......

Another thing.....instead of counting on the bulbs to be your test meter, use a meter on the wires and be positive of the results.
 
"AzPete" said:
It kinda sounds like the wire codes may be backwards or wires crossed in the new pigtail. You 1-3 results sound like the brakes are activating the parking light s in the dash. Bet the front park lights were on too. Also, item 3....are you 100% positive the brake filament was lit and it was not the tail light filament you were mistaking for the brake lights......

Another thing.....instead of counting on the bulbs to be your test meter, use a meter on the wires and be positive of the results.
Click to expand...

Today I intend to check both old and new pigtails to see if the continuity is the same. I was going to just reverse the wires to see if that fixed it, but I wasn't sure what would happen if I did...

As for #3, I based that on a brighter light.
 
I remember being told once that all the tail lights on these cars and the gauge lights go through the switch in the steering column.

I am not saying you need to mess with that, I am saying that if you have something crossed or not right in the back it will cause what you describe. Could also cause unexpected damage.

I agree with Pete. Reason is #4 on your list. There are only two combinations to play with have you tried reversing wires.

Also I would try putting it back the way it was and check all the grounds. Paint could be in the way and not getting a good ground on the left.

Recently found that a ground wire in a place you would never expect can cost hundreds of dollars in parts and part replacement that is not needed. (My daughter's S10 $500)

Mel
 
The fact that everything works fine with the older pigtail from the coupe, leads me to believe it's something in the new ones... I just can't figure out what, or why...
 
I miss understood you didn't realize that you had two sets of pigtails you were working with.

Use the set that works.

Mel

Sent from my Droid using Tapatalk
 
"guruatbol" said:
Use the set that works.
Click to expand...

That's what I'm doing. I tested all three and they checked out the same, but the only one that works correctly is the old one. Maybe it's in that housing...
 
It could possibly be that the base in the socket has worn and is twisting a bit as the bulb is installed. This can give several odd results. It should have a locking tab to hold it into position down in the socket.
 
"AzPete" said:
It could possibly be that the base in the socket has worn and is twisting a bit as the bulb is installed. This can give several odd results. It should have a locking tab to hold it into position down in the socket.
Click to expand...

Next I'll try one of the older housings, from the coupe, with a new pigtail...
 
You must log in or register to reply here.
Back
Top