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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / April 2007

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Electrical problems (yay...)

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bobar3425 - 06 Apr 2007 20:33 GMT
I Can't get my headlights to work. I have a 1968 mustang, and I'm
pretty sure all the wiring is original. I replaced the headlight
switch because that also controlled the dash lighting level, which
would flicker as I juggled the switch. The headlights still don't work
(and didn't before the new switch). After lots of testing, I have
found that at the headlight bulb, there is a voltage reading on the
negative lead. (the headlight plug has three leads, hi lo and ground,
and either lo and ground or hi and ground both have voltage readings
at the same time depending on where the beam selector is set) Because
of this, I think there are some crossed wires somewhere in the loom.
Does this sound reasonable to you or have I over looked something? Is
it hard to rewire parts of electrical systems? Also- there are a few
other electrical problems with the car, and the wring is all very old,
is it worth my time to buy one of those painless wiring kits to rewire
the entire car and can I even do it? Can I be cheap and buy a
universal ford wiring kit or do I need to spend more money and get a
vehicle-specific 1968 ford mustang wiring kit? thanks for the info
everyone!
Scott Dorsey - 06 Apr 2007 21:30 GMT
>I Can't get my headlights to work. I have a 1968 mustang, and I'm
>pretty sure all the wiring is original. I replaced the headlight
[quoted text clipped - 5 lines]
>and either lo and ground or hi and ground both have voltage readings
>at the same time depending on where the beam selector is set)

That's good.  Are you using a digital meter or are you using an analogue
meter?  Try again with a test bulb and see what happens when you measure
between the high beam pin or the low beam pin and a real ground, like the
block.

>Because
>of this, I think there are some crossed wires somewhere in the loom.

Maybe, but if you are using a DVM and there is any tiny leakage voltage
you will see it.  This will cause all kinds of indications like the one
you describe.

Maybe your ground is open.  Maybe your headlight relay is bad.  What
do you see on the headlight relay with the test lamp?

>Does this sound reasonable to you or have I over looked something? Is
>it hard to rewire parts of electrical systems? Also- there are a few
[quoted text clipped - 4 lines]
>vehicle-specific 1968 ford mustang wiring kit? thanks for the info
>everyone!

Old wiring can be okay, or it can be a total disaster.  I have never used
any of the kids, and have only made the body harnesses up by hand.  It's no
fun.  

Find the problems one at a time... if one of the problems turns out to be
deteriorating cable, then it's time to replace harnesses and looms.
--scott

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"C'est un Nagra.  C'est suisse, et tres, tres precis."

Mike Romain - 06 Apr 2007 21:34 GMT
I would be checking the dimmer switch out.  If it's that floor one, they
die all the time.  The aftermarket ones are crap so if you need I would
try to get OEM.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos:  Non members can still view!
Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
(More Off Road album links at bottom of the view page)

> I Can't get my headlights to work. I have a 1968 mustang, and I'm
> pretty sure all the wiring is original. I replaced the headlight
[quoted text clipped - 14 lines]
> vehicle-specific 1968 ford mustang wiring kit? thanks for the info
> everyone!
bobar3425 - 06 Apr 2007 23:48 GMT
thanks guys. I already tested the floor dimmer and it was fine. The
headlight relay is fine too. I'm pretty sure I've narrowed it down to
the segment of circuitry between the dimmer and the lamps.
Scott Dorsey - 07 Apr 2007 01:08 GMT
>thanks guys. I already tested the floor dimmer and it was fine. The
>headlight relay is fine too. I'm pretty sure I've narrowed it down to
>the segment of circuitry between the dimmer and the lamps.

Does that include the lamp grounds?
Does that include the connectors?  The connectors are far more apt to fail
than the wiring.  If both high and low beam is gone, the ground is the only
thing common to both once you get past the switch.
--scott
Signature

"C'est un Nagra.  C'est suisse, et tres, tres precis."

Mike Romain - 07 Apr 2007 15:59 GMT
> thanks guys. I already tested the floor dimmer and it was fine. The
> headlight relay is fine too. I'm pretty sure I've narrowed it down to
> the segment of circuitry between the dimmer and the lamps.

I would take it that you have full voltage going into and coming out of
one of the wires on the floor dimmer then?  I backfeed the plug with my
meter to check this.

The reason I ask is because when the headlight switch dies, it normally
takes out the spade connector in the plug on the harness side too.

It would also be very unusual for both the high and low beam wires to be
broken between the dimmer and the lights.

Does the body have a ground strap or cable that is broken?  I test that
using a booster cable between the battery negative and the body or even
the black wire on the headlight.

Your 68 has a headlight relay?  They can be sneaky for having a corroded
pin or it's socket on them.  Does it click when the switch is thrown?
Is there then power coming out of it?

What about the fuse link for the headlight harness?  Their should be
some 8" or so fat soft rubber coated wires with one loop end and a fat
tube crimp on the other end bolted to the solenoid on the fender where
the battery cable connects to it.  This is a safety link in case of a short.

If blown, it should flop loose and it might show a black mark on it. It
will not show continuity with a meter or show voltage past the tube
crimp when blown.  The headlight fuse link wire is a 14 ga. one
protecting the 10 ga. harness.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos:  Non members can still view!
Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
(More Off Road album links at bottom of the view page)
ixbeavisxi@yahoo.com - 07 Apr 2007 18:52 GMT
> I Can't get my headlights to work. I have a 1968 mustang, and I'm
> pretty sure all the wiring is original. I replaced the headlight
[quoted text clipped - 14 lines]
> vehicle-specific 1968 ford mustang wiring kit? thanks for the info
> everyone!

If you have power at the ground side of the circuit, then the
lamp(lamp) is not getting a ground, so you have to have an open
somewhere at the ground circuit. try and ground one of the ground
terminals of the lamp. Find out which of the two lamps provides the
constant ground, if you do this then both headlights will come on.
 
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