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[Shelby]

When I purchased my '66 Mustang, I was well aware that I didn't have a left turn signal (hence the big ugly 'Rejection' sticker on the windshield) because of something in the wiring harness.  I thought it would be a quick fix.  However, the person who owned it prior to me toyed with the wires and apparently wired them backwards (according to a friend of mine)

He took a look at the wires and spliced them.  After he spliced them, we tested the lights.  I still don't have a turn signal.  The parking lights work fine.  But when I turn the headlights on they over ride the parking lights.  I don't know what else could be wrong with it.  He said something may be wrong with ground wire or alternator.  I'm not sure, since I don't mess much with wiring in a car.  

Any ideas on what might be wrong with it?

[Thierry]

The only way to find out what's wrong is to test the wires with a multimeter. Check the power wire at the light bulb with one end of the meter on the wire the other one in a non painted location of the body like a bolt. If you get 12 V on this wire then you have a ground problem. If not you can locate the appropriate  
fuse in the fuse box and test both ends to see if you have any power. If you do the problem comes from the wire runing from the fuse box to the signal light.
Someone may have a better idea to fix this problem but this is the way I would do it. Good luck and let us know if you get it to work.

[Shelby]

I borrowed a multimeter and my buddy and tried out what you suggested.  The ground wires are fine.  I'm glad you suggested that so I didn't have to replace a perfectly good harness.  We've narrowed it down to one thing:  the turn signal switch.

It has to be.  You see, the boy I bought her off of replaced the steering wheel.  Of course, the steering wheel he bought was different, so a completely new steering column had to be used (it's not made for a '66 Mustang).  We think that he may have unhooked something or fouled something up in the process of changing it and the problem didn't show up until later.  That's the only other thing we can think of that could possibly keep the turn signal from working.  I'm more than likely going to have to take her somewhere to get this figured out.  Know of anything else that may be the cause?   :-(

[Thierry]

The switch might be the right place to look at especially if as you say the steering wheel and column are not original but it can also come from the relay. I am not sure how they work but they should not be very expensive and you may replace it to see if it makes any diference or you can take your steering wheel and switch apart to check if you have any power on the wire connected to the switch and coming from the battery (meter connected on the wire and the ground on the body). If there is power the problem is between the switch and the signal light. If not it is between the switch and the battery.

[Shelby]

Well...after what seemed like forever, we finally figured out what was wrong with it.  

The signal light wires were fried.  Boy, do I feel dumb.  I met a boy that helps his stepfather restore hot rods, and he had a multimeter (I think) different from what Eric had.  Aaron told me the problem was the wires in the signal light itself.  We replaced it and presto...turn signal.

She passed inspection.  However, when I press the brakes, the parking light comes on on the left side.  It never ends, does it?  I think that this has something to do with the harness this time.  I'm pretty sure Aaron installed the light correctly.  She's driveable and I just ride with my lights on so there isn't a question mark to oncoming traffic when I brake.  I would like to get this fixed in the near future.  Any suggestions on this one?  Should I go ahead and replace the harness, which, by the way, has been cut and spliced and taped in so many different places?  Apparently whoever did the wiring on her during restoration didn't know what they were doing.

[Thierry]

Having a parking light staying on all the time is not bad and you may be able to fix it. What is bad is having a wiring harness cut and taped everywhere. Moisture can get the wires corroded resulting in more resistance (loss of power) and heat. Worse case would be a shortcut in your electrical system. The best thing to do is to replace the whole harness if you don't want to see your mustang burning in flames. I am not saying your car is dangerous but this scenario may happen and I think the investment would be worth it.

[Shelby]

Thank goodness you said something.  I browsed a few places in search of a new harness, and I found one.  It's about $90, and I've got someone to put it in for me, so it's all good.  All I have to do is wait until my insurance bill comes.  Heh.  But anyway, thanks for your help.   :-D

[racedraper]

will this help?

[racedraper]

and

[racedraper]

and

[Thierry]

Very nice scans. I am sure they will be very usefull to Sixty6.

[racedraper]

well they are for 66 :-D . i can also post for all years from 641/2 thru 73 if you want for future use.

[BADBOBB]

HEY RACERAPER, SAW YOUR WIRING DIAGRAMS LAST NIGHT. WONDER IF YOU WOULD POST SAME FOR 1967 MUSTANG. MY PROBLEM IS AS FOLLOWS,
HEAD LIGHTS, FAN, WIPERS, EMERG. FLASHERS, ALL OK.
TAIL LIGHTS, TURN SIGS, PARK LIGHTS, BRAKE LIGHTS, HORN DO NOT WORK. ALL WIRES APPEAR TO HAVE CONTINUITY. I JUST GOT HOLD OF WIRING DIAGRAM FOR 66 STANG. MINE IS A 67. AM HOPING THAT I CAN TRACE PROBLEM THROUGH THAT. THIS THING HAS BEEN MONKYED WITH. I THINK THAT THE HORN WIRE GOING TO LIGHT SW. SHOULD BE HOT, THUS SUPPLYING POWER TO TAIL LIGHTS ETC, WHEN SWITCHED TO ON POSITION.
I CAN CHEAT POWER TO THESE ITEMS BUT WOULD PREFER TO REPAIR CORRECTLY.
TERMINALS ON LIGHT SW. ARE, "B"(BATTRY),"A"(ASCESSORY),"P"(PARK LIGHTS),""R"(REAR LIGHTS),"H"(HEAD LIGHTS), "I"(INSTURMENT LIGHTS), "D1"(DOOR LIGHTS),"D2"(DOME LIGHT).
WIRES COMEING INTO "B"+"D1" ARE ALWAYS HOT.
NO POWER TO ALL OTHERS.
TURNING H.L. ON, "B" HAS CONT. TO "H".
TURNING DOME LIGHT ON "D1 HAS CONT. TO "D2".
TURNING ONLY PARK LIGHTS ON, "P" HAS CONT. TO "R"+"A".
TURNING ON DASH LIGHTS "D" HAS CONT. TO "R"+"P"+"A".
??
BAD

[racedraper]

you asked for it. Hey boss man I am going to post all diagrams from 641/2 thru 73 so if you want to make it a forum buy itself or a stick one go ahead

[BADBOBB]

HEY RECED.
..... WAITING FOR EARLY MUSTANG WIRING DIAGRAMS.
HAVE THEY BEEN POSTED?
I AM NEW TO SITE, I MIGHT BE LOOKING IN WRONG PLACE.
MINE IS A 67, CURRENTLY TURN SIGS ABD GAS GAGE DO NOT WORK
BAD

[Thierry]

Yes racedraper did post the diagrams from 64 to 69 and the one for your car can be seen here:
Wire diagram for 67 Mustangs
You can click on the images to enlarge them.