Lighting issue // Electrical demon - Ford Mustang Forums : Corral.net Mustang Forum
 
LinkBack Thread Tools Display Modes
post #1 of 4 Old 04-14-2012, 08:05 AM Thread Starter
Registered User
 
Trader Feedback: (0)
Join Date: Nov 2011
Location: Utah
Posts: 40
Lighting issue // Electrical demon

Alright...Im going to try and explain this as best I can...

Working on my 1968 Mustang:

Both filaments light up at the same time when I push on the brakes. Also if I turn on my lights (Driving at night) both filaments light up so there is no way to tell when I push the brakes as there is no change in brightness. Why?!

Also, when I push the break pedal, my instrument culster lights turn on.
What else could I do or check or change to fix this?

Things I have looked into // Changed:

Changed - Brake light switch
Changed - Headlight switch
Checked wires to ensure that there is no wearing through or any bare wire contact.
Changed - Bulbs
Checked // Changed fuses

What else can I check because I would really like to be able to drive my car at night without the risk of having some dip#### rear end me.

Thanks for any and all help,

Trevor

Trevor.801 is offline  
Sponsored Links
Advertisement
 
post #2 of 4 Old 04-20-2012, 06:21 AM Thread Starter
Registered User
 
Trader Feedback: (0)
Join Date: Nov 2011
Location: Utah
Posts: 40
Anyone?

Trevor.801 is offline  
post #3 of 4 Old 04-23-2012, 02:09 PM
Registered User
 
Trader Feedback: (9)
Join Date: May 2002
Location: New Braunfels TX
Posts: 4,477
Well you have your brake light circuit and your taillight circuit basically wired together. I bet that your headlights also come on when you step on the brakes because low-beams and taillights are usually just one big circuit along with your instrument cluster.

Both filaments should not be coming on which also indicates that you have the power wires from the brakes and taillights tied together somewhere.

You should have 3 wires going to your rear bulbs. 1 ground, 1 taillight power, and 1 brake light power. On one side you may see 5 wires, because the taillight power and brake light power are doubled up, but this is really just where the splice going to the other side is, so there's really only 3 unique wires.

Check for continuity between the Taillight power, and Brake light power wires (everything in the car off) and you will almost certainly find that you have continuity.

First thing to do is one at a time, remove a bulb, and see if the continuity goes away. If it does that means the B and T wires are crossed at that light socket or somewhere upstream of that light socket, causing the 2 circuits to basically become one.
EDIT: When I draw this out I'm not sure if crossed wires at 1 bulb would cause both filaments on both bulbs to light or not. If it did I think you'd have the brake filament brighter on one side, and the taillight filament brighter on the other.
EDIT EDIT: Now I'm pretty sure crossed wires wouldn't matter, so nevermind on my first guess.

If you're not lucky the problem is somewhere else but the basic problem is the same. The wires are literally connected together somewhere, or they're crossed up at a point where both circuits are at a common place, like at the taillight bulbs.

'94 GT, White, Cobra hood & bumper cover, '95R wheels
393w, Vic Jr 60cc, XE282HR, Victor 5.8 EFI, 80# injectors, Hooker LT 1 3/4 to 3", Borla proXS
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

T56 w/ AJE xmember, McLeod street twin, MM/Bilstein '03 IRS, JRi Agent47 SLA
Megasquirt

Last edited by seijirou; 04-23-2012 at 02:39 PM.
seijirou is offline  
Sponsored Links
Advertisement
 
post #4 of 4 Old 04-23-2012, 02:37 PM
Registered User
 
Trader Feedback: (9)
Join Date: May 2002
Location: New Braunfels TX
Posts: 4,477
Here's my drawing lol.



So imagine stepping on the brakes. Power comes down the red wire on the left and is spliced right there so it also goes over to the right. On the right it should be on the B but it's accidentally on the T instead.

On the left the B filament lights up, and on the right the T filament lights up.

Here's where I'm not 100% sure. On the right side the power coming in the T can back-track through the bulb and also light up the B and if it did the ground path for right's B would be through left's T. That would explain all 4 lighting up, but the 2nd "pair" should be dimmer. And even without crossing the wires, backtracking is still possible so my first guess of crossed wires isn't making much sense...

Also I'm pretty sure electricity wouldn't back-track like that, the ground for right's T is the G and it's right there. The path to back-track has high resistance because of 2 filaments, and if the local Ground is good there's no reason why all current wouldn't ground right there.

Wait a second, maybe lacking a ground is the problem. Take ground away and now there's a reason for electricity to follow a strange route.

Even if the wires aren't crossed up, if the right bulb's ground wire is broken or bad, now the ground path for power going to B on the right is to back-track through the bulb, through the T filament on the right, which will also flow through the T filament on the left lighting it up, and ultimately through the left bulb's ground.

Check your ground wire on both of your rear lights and make sure one of them isn't bad.

I'm just making stuff up over here though, none of this theory applies if the circuits don't share a common ground. I wish I had a 68 wiring diagram.
Attached Images
File Type: jpg crossed taillights.jpg (26.2 KB, 12 views)

'94 GT, White, Cobra hood & bumper cover, '95R wheels
393w, Vic Jr 60cc, XE282HR, Victor 5.8 EFI, 80# injectors, Hooker LT 1 3/4 to 3", Borla proXS
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

T56 w/ AJE xmember, McLeod street twin, MM/Bilstein '03 IRS, JRi Agent47 SLA
Megasquirt

Last edited by seijirou; 04-23-2012 at 02:41 PM.
seijirou is offline  
Sponsored Links
Advertisement
 
Reply

Bookmarks

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Ford Mustang Forums : Corral.net Mustang Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
Troubleshooting dash lighting issue. darkmach1 Electrical & Wiring 5 11-13-2011 05:55 PM
1994 V6: Which PCM pin is VSS? svtlightning208 94/95 Tech 4 09-18-2011 09:16 PM
Electrical issue kim Lounge 4 07-30-2011 11:54 AM
electrical issue... 2vFobra GT & SOHC 1 05-09-2011 03:19 AM
Electrical issue after engine install Prochargedsnake SVT & DOHC 1 02-21-2011 06:04 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome