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Hey guys, I need some help figuring out my runner lights wiring. I have a video showing what's up.
basically I'm not getting power. And there are some wires that have been cut off, so I need to know where these wires are supposed to go. You can see in the video any advise or pictures, or videos would be amazing!
What year is the truck? A '74 or '75 by any chance? Just curious at this point, but it might help in diagnosing wires down the road.
This truck did have the cab lights from the factory, yes? Not just something that you or a PO added after the fact by any chance? Looks factory, but very often Ford would include all the wiring for all the options in one harness, and only complete it when that option was checked off. So just checking that angle.
The little silver box bolted under the dash with the wires is the light relay. There should be a Black wire that actually sends power to the lights when the relay is energized. Sounds like you found that wire, but it's not connected in a couple of spots. But perhaps you're lucky in that those open connectors are for the Canadian-only mirror marker lights. Maybe...
There is also a Black w/white wire that will have power all the time. This runs up to the starter relay/solenoid and has it's own fusible link. If you put the probe of your volt-meter into the socket/connector with the Black w/white wire and see power there, your fusible link is good. If no power, then check up at the starter relay.
The Brown wire is the trigger wire. It gets power only when the headlight switch is pulled, and literally is the signal to turn the lights on.
If you do not have power when the light switch is pulled, there could be a couple of things going on.
One is that the wire or the switch is buggered, OR, your truck has the separate switch somewhere. I've never actually seen one of those, but it's in the diagrams (at least for '74) so maybe it exists. Someone will know I'm sure.
So test that relay's plug again and see when, and if you get 12v to the switch.
Can you see if one of those unused black wires is coming down the A-pillar from the roof? If so, that's the wire to feed all the cab lights on top and should be connected to the Black wire coming off of that relay.
That's all I've got for the moment. Never troubleshot one of these systems before, but it looks pretty straightforward.
Let us know what year your truck is first though, in case there are variations.
Thanks for the reply, it's a 1973, and yeah I think they are factory.
There is a green and black wire that comes out into the engine bay that gets constant power, but I have to fallow that cord to make sure where it comes from.
I think it hooks up with an orange cord and the windshield wiper switch, but I have to look again.
That relay with the brown cord also has the two black
cords. When the lights are on the brown cord coming out of that relay gets power, but not the other two black wires (see my detailed illustration). 😁😭
after laying it out like this it definitely looks like it might be that relay..
I guess I could just splice that brown wire directly to the cab lights, but I don't want to mess up anything that's not already broken lol.
If you have anymore advise let me know guys! Thank ya!
It might just be as simple as the relay is malfunctioning. Or it's not getting a good ground through the case to the dash.
I don't know for a fact that it does ground through the case, but many of the Ford relays that look like that do happen to ground through the mounting screw.
When you pull the headlight switch to the first notch, do you hear or feel the relay click? Put your hand on it and move the light switch in and out a few times.
If it's not clicking, you may just have to replace the relay.
You can verify that it's all working by pulling the connector off of the relay, then jumpering the Brown wire to one of the Blacks, then the other.
If the lamps up top light up when you turn on the headlight switch, then you know the break in the system is the relay. You can replace it with a proper Ford replacement (recommended) or even put in a standard "Bosch type" relay instead.
The latter are maybe less expensive and maybe easier to find, but it's nice to keep it all Ford at this point so the connector slips right back on without modification.
Doing all this you might even find out that the wires are loose in the connector and not even have to replace anything.
Another interesting variation then. What year model was that pic taken from?
All my diagrams show a relay, and Sam's got what looks to be a relay with the wires in question running to and from it.
Might explain the extra unused connectors he's got though.
Just looked closer at the '78/'79 wiring and it looks like the relay was used, but not in all cases. Some variation on with/without trailer lights, or stake-pocket marker lights (flatbed use apparently?).
Curiouser and curiouser...
But admittedly I don't always see the obvious when these diagrams take their multiple-choice twists-n-turns with different options. I'm finally getting comfortable reading the "with or without gauges" variations!
The pic is from my 78. I installed cab marker lights in all three trucks, and none had the factory relay. Perhaps you only got the relay with factory lamps.
Alright I took everything y'all were saying and really got under the dash, and I found out that the relay takes power via the brown cord from the light switch, then directs the power to the cab lights and what used to be a CB radio is my guess. But the previous owners chopped out the CB. When they did that I think it made the connections incomplete. So I could just go ahead and splice that brown wire directly to the cab lights. Which is how I THINK it was originally done like ole dudes picture. Thanks for that by the way.
It will probably be a minute before I actually get out there and do it, but I'll let y'all know how it goes.
