Front marker lights/turn signals

[machm1970 180]

Funny i just noticed this, the turn signals don't work when the lights are on. I'm referring to the ones housed in the front valance opening. The rest of the turn signals blink just fine, but these only blink if the headlights are off. Is this normal?

Thanks,

Matt

[RPM 1,190]

Sure doesn't sound normal to me.

[Mach1 Driver 560]

No that shouldn't happen, the side marker lights are on the park/on circuit from light switch R. I believe you lost a ground on one of the brake/turn-park 1157 bulbs. It could be in the front or back. 

[machm1970 180]

We might be talking about different lights, I'm talking about the ones under the grill and bumper, in the vanance opening.

Matt

[larryc94 38]

Still no, the ones in valance opening work no matter what lights are on.  The side markers also flash no matter what lights are on or off.  Check the ground on the passengers side radiator support (front)

[machm1970 180]

Is this the one you're referring to? It's the only one i can see on the passenger side radiator support.

Thanks for your help,

Matt

[larryc94 38]

Yes, take it off and clean any paint off

[Mach1 Driver 560]

Whoops, yep I misunderstood which lights. Machm1970 and larryc94 are correct. Its still the same senerio. You've lost the grounds for one or both of the front two turn signals/ park lights. Since the 1157 bulbs have two filaments in them, if you loose the ground, both filaments are still connected together at the base of the bulb, so it goes thru the Park filament and over to the bulb on the other side and to ground. If you turn the headlights on there is no path for the turn filament.

Its impossible to follow on the wire diagram (there is just too much going on), but on a schematic its much easier to see. See the attached page 3 of the schematic. Look at the left front light with two filaments. Its about in the middle, just below center.

Imagine that the grounds are not connected to chassis, but they are to themselves at the base of the bulb (that's how the bulb is made). The filaments are put in series and the power looks for a ground path, and finds it through the other Park filament. I'm not saying its the left front, that's just an example, it could be the right front. Anyway, look at the schematic and if you can follow the path it should become obvious. 

MUSTANG SCHEMATIC PG3.pdf

[machm1970 180]

I'm out of town at the Goodguys show, I will let you know whst I find out tomorrow. 

Thanks for all the help!

Matt

[larryc94 38]

That wiring diagram looks like it is for a 69.  The 70 is different, the side markers don't have  a ground to the body instead they are connected to the corresponding signal wire for that corner of the car.

When the park-headlight are on the marker grounds through the signal filament.  When the signal is on the pulse interrupts the ground so  the side marker flashes . The signal and marker alternate.

When park-headlights are off the and signal is on the side marker flashes at the same time the signal lamp does and grounds through the park filaments

 

Larry

[Brian Conway 264]

So does that mean if the signal filament is burned out/broken the ground is no longer working ?

[larryc94 38]

If the front signal/park light plug is disconnected the marker light goes out, only on a '70.  So I would say yes if the signal filament is burned the marker goes out.

 

There only 2 wires in the signal/park lamp plug, one for each and ground through the mounting

[Mach1 Driver 560]

3 hours ago, larryc94 said:

That wiring diagram looks like it is for a 69.  The 70 is different, the side markers don't have  a ground to the body instead they are connected to the corresponding signal wire for that corner of the car.

Yes it is a schematic for a 69. I neglected to put that on page 3. Not having a 70, I wasn't aware of the change. That's interesting- I like it! 

 

[machm1970 180]

I got home and cleaned the ground really well, no change.

Matt

[larryc94 38]

So does it light up and just no blink? Both Drivers and pass act the same?

[machm1970 180]

Yes

[larryc94 38]

They actually ground through the bumper, run a jumper wire to the body of the light and see what happens.

Do the rears flash?  How about the 4 ways

How did problem appear? out of blue, after something else done?

 

Larry

[machm1970 180]

Solved! I bought new marker lights from NPD a few months ago, they wired the plugs backwards! I ran a jumper wire between the plugs reversing the wiring and they work! Guess i will be calling NPD.

Thanks for all your replies.

Matt

[larryc94 38]

Marker lights? Turn signal/park lights...trying to make sense of this the markers use a 194 bulb with 2 wires that polarity wouldn't matter (those bulbs don't have a dedicated ground or hot)

[machm1970 180]

My front marker lights have dual filament bulbs, there's 3 wires for each side from the wiring harness going to a 2 prong plug. I'm not good with electrical, I unplugged them and ran jumper wires criss crossed across the plugs and they worked.

[larryc94 38]

The ones on the fender or the ones in the valance?

[Midlife 814]

10 minutes ago, machm1970 said:

My front marker lights have dual filament bulbs, there's 3 wires for each side from the wiring harness going to a 2 prong plug. I'm not good with electrical, I unplugged them and ran jumper wires criss crossed across the plugs and they worked.

In a 1970, both the front and side marker lamps use only two signal leads: running lights and turn signals.  When you say three wires from a two prong plug, this can be interpreted to mean 3 signal lines.  I believe what you are trying to describe are two leads, one of which has two wires of identical colors.

There is no true ground here, so changing the polarity should not make a difference.  Furthermore, there should only be one filament.

For a 1969, the wiring for the front (valence) lights are a bit different, with three signal lines, two filaments, but 3 prong plugs.

[larryc94 38]

9 minutes ago, Midlife said:

In a 1970, both the front and side marker lamps use only two signal leads: running lights and turn signals.  When you say three wires from a two prong plug, this can be interpreted to mean 3 signal lines.  I believe what you are trying to describe are two leads, one of which has two wires of identical colors.

The harness side for sig/park light in the valance has what Midlife describes as two same color  wires on the same pin and a single wire on the other

[machm1970 180]

Yep, that's what mine has.

Matt

[larryc94 38]

So it sounds like the park wire was lighting the turn filament (which is brighter) and the signal wire was lighting the park filament (which not as bright) and therefore when if the signal is flashing it won't be seen because the brighter filament is being lit by the park circuit.

Don't know if there wired different, 69 and 70 sig/park lights are different part #'s