Wiring? Taillights?

[stangracer85]

I Have A 85 Gt And Im Having Some Problems With My Taillights. When I Turn My Headlights On Just The Headlights Turn On...no Interior Lights Except For The Dome Light...no Instrument Lights! No Parking Lights! And No Taillights! But When I Press The Brake Pedal The Brake Lights Turn On. I Cant Figure Out What Could Be Wrong. I Checked All The Normal Fuses And All Is Good Now. Had One Blown One But Not Sure What It Went To Exactly Replaced It And Made No Difference. There Are Two Other Fuses In The Fuse Box...i Know One Is The Flasher Relay For The Turn Signals Which By The Way Do Work And The Other One Is A Rectangular Shape...i Dont Know What That Is For. Ive Been Trying To Figure This Out Forever And Just Getting Frustrated Now So Im Reaching Out To You All For Help.

 

[HISSIN50]

I would check the headlight switch itself. On the back will be one terminal for just parking lights. THis will either also include the instrument illumination wiring too, or it will be separate like on Foxes and SN's (I have not seen a four eye headlight switch). That is where I would start though. Your headlights work since that is a different position on the switch.

Good luck.

 

[stangracer85]

Ive Had To Replace The Headlight Switch Before...so I Did Buy Another One...brand New One Already Installed Just A Week Ago...even With That No Difference...i Just Left The New One In So There Was No Wandering If It Was That Part. How Can I Check To See What Wires From The Plug In Are For The Parking Lights And Which One Is For The Headlights Since At Least The Headlights Are Working??

 

[HISSIN50]

You can look at the schematics in the back of your repair manual or at the schematics on AZ's website.

I would remove the switch and backprobe the wires. You should see a constant feed to the switch and then with probing and a schematic, be able to see which wires do what. You will find one that is hot with the headlight switch all the way on (your headlights will be on). At that point, there should be one wire which does not appear to do anything and reads nothing or open. That wire's color should match the parking light wire color.

Now if you have juice to that point, you need to trace the parking light further. It should not be much further at all since the wire branches out into different directions. If one of those branches is bad, the other branches would work and provide other parking lights with light (unless your bad wire shorts to ground, which takes out the entire circuit).

Good luck.