machm1970 180 Report post Posted June 30, 2017 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 Quote Share this post Link to post Share on other sites
RPM 1,190 Report post Posted June 30, 2017 Sure doesn't sound normal to me. 1 clintonsn60 reacted to this Quote Share this post Link to post Share on other sites
Mach1 Driver 560 Report post Posted June 30, 2017 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. Quote Share this post Link to post Share on other sites
machm1970 180 Report post Posted July 1, 2017 We might be talking about different lights, I'm talking about the ones under the grill and bumper, in the vanance opening. Matt Quote Share this post Link to post Share on other sites
larryc94 38 Report post Posted July 1, 2017 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) Quote Share this post Link to post Share on other sites
machm1970 180 Report post Posted July 1, 2017 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 Quote Share this post Link to post Share on other sites
larryc94 38 Report post Posted July 1, 2017 Yes, take it off and clean any paint off Quote Share this post Link to post Share on other sites
Mach1 Driver 560 Report post Posted July 1, 2017 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 1 JayEstes reacted to this Quote Share this post Link to post Share on other sites
machm1970 180 Report post Posted July 1, 2017 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 Quote Share this post Link to post Share on other sites
larryc94 38 Report post Posted July 1, 2017 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 Quote Share this post Link to post Share on other sites
Brian Conway 264 Report post Posted July 1, 2017 So does that mean if the signal filament is burned out/broken the ground is no longer working ? Quote Share this post Link to post Share on other sites
larryc94 38 Report post Posted July 1, 2017 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 Quote Share this post Link to post Share on other sites
Mach1 Driver 560 Report post Posted July 1, 2017 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! Quote Share this post Link to post Share on other sites
machm1970 180 Report post Posted July 2, 2017 I got home and cleaned the ground really well, no change. Matt Quote Share this post Link to post Share on other sites
larryc94 38 Report post Posted July 2, 2017 So does it light up and just no blink? Both Drivers and pass act the same? Quote Share this post Link to post Share on other sites
machm1970 180 Report post Posted July 2, 2017 Yes Quote Share this post Link to post Share on other sites
larryc94 38 Report post Posted July 2, 2017 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 Quote Share this post Link to post Share on other sites
machm1970 180 Report post Posted July 2, 2017 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 Quote Share this post Link to post Share on other sites
larryc94 38 Report post Posted July 3, 2017 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) 1 RPM reacted to this Quote Share this post Link to post Share on other sites
machm1970 180 Report post Posted July 3, 2017 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. Quote Share this post Link to post Share on other sites
larryc94 38 Report post Posted July 3, 2017 The ones on the fender or the ones in the valance? Quote Share this post Link to post Share on other sites
Midlife 814 Report post Posted July 3, 2017 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. 1 doreenzb3 reacted to this Quote Share this post Link to post Share on other sites
larryc94 38 Report post Posted July 3, 2017 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 Quote Share this post Link to post Share on other sites
machm1970 180 Report post Posted July 3, 2017 Yep, that's what mine has. Matt Quote Share this post Link to post Share on other sites
larryc94 38 Report post Posted July 3, 2017 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 Quote Share this post Link to post Share on other sites