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Old 03-07-2018, 01:25 PM   #1
osks70
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Headlights inop

So i replaced the under dash harness and engine harness with American Auto Wire factory Harnesses on my 1970 c10. So now none of my lights work. When I pull on the headlight switch I lose Power at the fuse panel, (new headlight switch too). I do have the guages plug disconnected since I put in Dakota Digitals, does that plug have to be connected or modified to complete a circuit? Maybe I have a bad ignition switch? or the front light harness does not match the fuse panel? This one has me stumped any help would be great! thanks!

Last edited by osks70; 03-07-2018 at 01:59 PM. Reason: forgot year of truck
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Old 03-07-2018, 02:34 PM   #2
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Re: Headlights inop

Welcome aboard! Is the dimmer switch hooked up? How are you measuring the 12 volts at the fuse panel? Is it a new dimmer switch? How about the light switch is it new ? More than one board member has found new switches that don't work. You can find wiring diagrams for your truck if you do a search in the search box above and click the 67-72 circle.
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Old 03-07-2018, 02:46 PM   #3
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Re: Headlights inop

Is the dimmer switch part of the Headlight switch? Headlight switch is new. I have tried 2 switches thinking that was the problem. I am using a test light to check power.
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Old 03-07-2018, 02:47 PM   #4
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Re: Headlights inop

ok dimmer switch is mounted on the floor, I have a new one will install it in a bit to see if it is the problem.
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Old 03-07-2018, 02:57 PM   #5
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Re: Headlights inop

Quote:
Originally Posted by osks70 View Post
ok dimmer switch is mounted on the floor, I have a new one will install it in a bit to see if it is the problem.
Testing the dimmer switch couldn't be easier. If you can get it unplugged, jump the blue wire in the harness to either the tan or green wire and turn the HL switch on. The lights should come on. If they do then the dimmer is bad or both your lights are blown or their grounds are bad.
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Old 03-07-2018, 02:57 PM   #6
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Re: Headlights inop

ok new dimmer switch did not fix it, so with the headlight switch off I have power at the orange and red wires at the connector, with it on I have no power at the orange and red wires at the connector.
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Old 03-07-2018, 03:07 PM   #7
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Re: Headlights inop

The foot dimmer switch is part of the circuit between the headlight switch and the lights. The headlight power doesn't come through any fuses in the panel. There is a separate circuit for the dash lights and (if memory serves me well) the tail lights that is fused in the fuse panel. The red wire on the headlight switch is 12 volt power to the light switch for the headlights from the insulated terminal next to the battery. The blue on the switch is 12 volt positive power out to the dimmer switch.
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Old 03-07-2018, 03:17 PM   #8
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Re: Headlights inop

Use the test light to see if you have power on the blue wire at the dimmer switch with the headlight switch on. If you don't then the headlight switch is bad or the blue wire is open to the dimmer switch. I would jump a wire from the red wire on the HL switch to the dimmer switch connector on the blue wire and see if the lights work.

HO455 is correct, the orange wire is the power feed wire for the tail lights, dash lights, and the dome light as well as the stop light switch.
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Old 03-07-2018, 03:38 PM   #9
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Re: Headlights inop

Make sure to recheck all your ground connections too. Make sure there is not a build up of paint under the terminals and that all connections are tight. How many physical grounds do you have connected? You need a ground strap from the engine to the cab, from the cab to the frame, from the engine to the frame and the core support to the frame. You can never have enough grounds. My 2.

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Old 03-07-2018, 04:21 PM   #10
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Re: Headlights inop

Here's a pretty good diagram of the wiring circuit with the headlight switch on the far right, and the fuse panel on the lower right with the red wire from the battery feeding the orange wire.



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This one shows the fuse panel to the left of the headlight switch bottom center, without the arrows. You can follow the blue wire from the headlight switch to the dimmer switch.

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If you save them to your hard drive you should be able to enlarge them for a better view.
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Old 03-07-2018, 04:33 PM   #11
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Re: Headlights inop

thanks for the diagrams. ok so no power to the blue wire at the dimmer switch with headlight switch on or off. I jumped the red wire from the headlight switch to the the blue wire on the dimmer switch and no headlights came on.
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Old 03-07-2018, 04:34 PM   #12
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Re: Headlights inop

how is the headlight switch grounded?
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Old 03-07-2018, 05:12 PM   #13
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Re: Headlights inop

The switch itself does not need to be grounded.
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Old 03-07-2018, 06:28 PM   #14
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Re: Headlights inop

ok thanks, any more ideas? this one has me pretty stumped. again all new under dash American Wire Harness factory style and all new engine American Wire Harness factory style. Maybe something in the front light harness?
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Old 03-07-2018, 07:33 PM   #15
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Re: Headlights inop

The headlight switch has to be grounded to light the dome when it is turned fully C/W. All the dome light switches are on the ground side and the orange wire from the fuse panel dome light fuse gives the dome light it's power.

Did you jump the red wire at the dimmer switch to the tan or green wire or just to the blue wire. If the dimmer switch is OK then one of the beams should have come on because the dimmer just selects high or low beam. In any case you need to figure out why the blue wire has no power when the headlight switch is on.

Do any of the tail lights or dash lights work? Or the front parking lights?
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Old 03-07-2018, 08:33 PM   #16
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Re: Headlights inop

none of the lights work. So the red wire at the headlight switch should be constant power correct? why when i pull headlight switch out to the on position I lose power at that wire?
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Old 03-08-2018, 12:07 AM   #17
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Re: Headlights inop

The red wire comes straight from the battery,alternator, regulator junction. The only way you could lose power there is for the battery to have a bad cable connection or the fusible link that goes to the right fender junction to blow. Unless the connection at the fender junction is bad going to the Bat, alt reg junction.

Here is how the wires run. From the battery fender junction.


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The red wire going to the right of the junction is the feed wire for the cab. It goes through the firewall block and forms a junction with three other wires shown here. Don't pay any attention to the arrows, they are for other problems.

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One of these red wires feeds the horn relay, one goes to the key switch for key on power, and one goes down to the fuse panel to feed the key off orange wire power, and the last one is the one which feeds the headlight switch. These are shown here.


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Do you have power anywhere. Horn, ignition, turn signals, hazards, etc?
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Old 03-08-2018, 09:01 PM   #18
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Re: Headlights inop

yes have power everywhere that red wire leads to until headlight switch is turned on, with it on i check power on the engine firewall side of the harness and i have power there, but on inside of cab fusebox side no power. I am starting to thing this harness is garbage.
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Old 03-08-2018, 09:42 PM   #19
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Re: Headlights inop

You may have a bad plug in the headlight switch. Try jumping the red wire and the blue wire there and see if the red wire loses power when you do. If it does you will have to trace it back to the junction with the other red wires and look for a bad connection.
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