Trailer Turn Signals
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Freshman User
Joined: Jan 2002
Posts: 37
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From: Whitefish Bay, WI
Trailer Turn Signals
I've been trying to get my truck's trailer tow lights working and am currently stumped. I did a search on the forumns and couldn't find an answer to my question.
At first, I had no power at all to either trailer wiring connector (4 or 7 pin). I checked the fuses and had one out under the hood and one out in the central fuse box under the dash.
After that, I now have power to the running lights and the battery charge line on the 7 pin, but no turn signals or brake lights. I didn't check if i'm getting reverse or a signal from the brake controller.
For reference, I've been checking for voltage at the rear connectors with my multimeter.
Any idea what else it could be? I know there are relays in the fuse box under the hood for trailer turn signals. Is there a way to see if these are bad?
Any help is appreciated.
Jeremy
At first, I had no power at all to either trailer wiring connector (4 or 7 pin). I checked the fuses and had one out under the hood and one out in the central fuse box under the dash.
After that, I now have power to the running lights and the battery charge line on the 7 pin, but no turn signals or brake lights. I didn't check if i'm getting reverse or a signal from the brake controller.
For reference, I've been checking for voltage at the rear connectors with my multimeter.
Any idea what else it could be? I know there are relays in the fuse box under the hood for trailer turn signals. Is there a way to see if these are bad?
Any help is appreciated.
Jeremy
Post Fiend
Joined: May 2006
Posts: 10,007
Likes: 4
From: Central Florida
Check out this link to make sure your pinned right. http://www.trailerwiring.com/inst/48485.pdf
The first thing I would check for is, is this a factory setup? Follow the wiring up to spare tire, OE wiring plugs into the 7 wire plug, after market have a pig tail off the large round (gray) plug. Aftermarket units sometime have a diode pack, when the diodes fail, you loose turn and brake lights.
Also what are you using a ground? The center pin is reverse, the vertical on each side are your turn signals. For testing, I would go off the frame.
Ideally the relays under the hood should click with your hazard lights. If not, you can pull the relays and see if they have 12v+ on pin 86 and ground on 85 in the socket when the brake lights are on. If yes, then you need to have power on pin 30 or 87 of the socket.
You can try putting 12v to pin 86 and ground on 85 (there might be a diode so be sure to power in this direction.) It should click as soon as you apply power. Then you can check for continuity on pins 30 and 87.
The first thing I would check for is, is this a factory setup? Follow the wiring up to spare tire, OE wiring plugs into the 7 wire plug, after market have a pig tail off the large round (gray) plug. Aftermarket units sometime have a diode pack, when the diodes fail, you loose turn and brake lights.
Also what are you using a ground? The center pin is reverse, the vertical on each side are your turn signals. For testing, I would go off the frame.
Ideally the relays under the hood should click with your hazard lights. If not, you can pull the relays and see if they have 12v+ on pin 86 and ground on 85 in the socket when the brake lights are on. If yes, then you need to have power on pin 30 or 87 of the socket.
You can try putting 12v to pin 86 and ground on 85 (there might be a diode so be sure to power in this direction.) It should click as soon as you apply power. Then you can check for continuity on pins 30 and 87.
Thread Starter
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Freshman User
Joined: Jan 2002
Posts: 37
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From: Whitefish Bay, WI
I checked the relays - they click when the turn signals are on.
I rechecked all the fuses. In the passenger compartment fuse box I've checked locations: 20, 28 and 38. In the power distribution box I've checked locations: 9 and 20.
For setup I'm using the factory 4/7 pin combo connector. I have a prodigy brake controller in the truck thats never been used by me - came with the truck.
I rechecked all the fuses. In the passenger compartment fuse box I've checked locations: 20, 28 and 38. In the power distribution box I've checked locations: 9 and 20.
For setup I'm using the factory 4/7 pin combo connector. I have a prodigy brake controller in the truck thats never been used by me - came with the truck.
Hotshot
Joined: Jan 2004
Posts: 19,762
Likes: 1,079
From: St Louis
Focus on the circuit for F9 in the BJB. It supplies lamp power to the relays when they are energized.
If the fuse is not blown (swap it anyway), check to be certain one leg of the fuse is ALWAYS HOT, then check continuity between the other fuse terminal and the COM terminal of both brake/turn signal relays.
I'm betting that, for whatever reason (ie, faulty fuse, bad fuse terminal, or open feed wire), you're missing F9 power at both relays.
Steve
If the fuse is not blown (swap it anyway), check to be certain one leg of the fuse is ALWAYS HOT, then check continuity between the other fuse terminal and the COM terminal of both brake/turn signal relays.
I'm betting that, for whatever reason (ie, faulty fuse, bad fuse terminal, or open feed wire), you're missing F9 power at both relays.
Steve
Junior User
Joined: Mar 2008
Posts: 97
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From: Sammamish, WA / U.S. VI
I had a similar problem last week. I connected the F250 to my boat for the first time ever. I couldn't get the bloody lights to work. I inserted a tester and verified that the signals were properly coming through the tow harness but when I would connect the trailer nothing would work.
I went and bought another adapter plug thinking it was the next logical source of failure given the truck was sending the signals. Longer story short, I eventually figured out that my particular problem was because I didn't have my headlights on!!! Strange but true. It turns out that with our other tow vehicle (Volvo XC90 V8) we have automatic DRLs and I never thought about the need for lights to be on for the trailer wiring to work but it seems to be the need for my SD. I haven't had any trailer lighting issues since.
I went and bought another adapter plug thinking it was the next logical source of failure given the truck was sending the signals. Longer story short, I eventually figured out that my particular problem was because I didn't have my headlights on!!! Strange but true. It turns out that with our other tow vehicle (Volvo XC90 V8) we have automatic DRLs and I never thought about the need for lights to be on for the trailer wiring to work but it seems to be the need for my SD. I haven't had any trailer lighting issues since.
Hotshot
Joined: Jul 2003
Posts: 12,177
Likes: 40
From: Newport, WA
You shouldn't need to have the lights on for the trailer lights to work... that's a strange one.
To the OP, triple check all your fuses- I nearly pulled my hair out doing this each time I've had to do it. Unhook the trailer, check every fuse, test at the plug, then hook the trailer back up and see what happens once you get the truck working right.
To the OP, triple check all your fuses- I nearly pulled my hair out doing this each time I've had to do it. Unhook the trailer, check every fuse, test at the plug, then hook the trailer back up and see what happens once you get the truck working right.
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Postmaster
Joined: Jan 2005
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From: Peoria, IL
Like he said, check every fuse, not just the ones that are marked for the lights. Ford does a pretty poor job of labelling the fuses for everything that runs off them.
Also I recommend using a fuse tester, or multimeter to check them, as a visual check isn't always good enough with these mini fuses.
Also I recommend using a fuse tester, or multimeter to check them, as a visual check isn't always good enough with these mini fuses.
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Hotshot
Joined: Jul 2003
Posts: 12,177
Likes: 40
From: Newport, WA
Like he said, check every fuse, not just the ones that are marked for the lights. Ford does a pretty poor job of labelling the fuses for everything that runs off them.
Also I recommend using a fuse tester, or multimeter to check them, as a visual check isn't always good enough with these mini fuses.
Also I recommend using a fuse tester, or multimeter to check them, as a visual check isn't always good enough with these mini fuses.
Hotshot
Joined: Jan 2004
Posts: 19,762
Likes: 1,079
From: St Louis
There's no point in dinking with every fuse. Just check the one I said to check. In reality, Ford's service documents do a VERY good job of getting this type of info correct.
rdollie: You have a bad ground. Probably, one that is relying on the hitch ball. There is no logical reason that DRL and the headlights have to be on to make the brake/turn signals work. Electricity doesn't work that way - I've been doing electronics and electrical systems for 30 years, I do know a thing or two about them....
Steve
rdollie: You have a bad ground. Probably, one that is relying on the hitch ball. There is no logical reason that DRL and the headlights have to be on to make the brake/turn signals work. Electricity doesn't work that way - I've been doing electronics and electrical systems for 30 years, I do know a thing or two about them....
Steve
Freshman User
Joined: Oct 2007
Posts: 46
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I've been trying to get my truck's trailer tow lights working and am currently stumped. I did a search on the forumns and couldn't find an answer to my question.
Any idea what else it could be? I know there are relays in the fuse box under the hood for trailer turn signals. Is there a way to see if these are bad?
Any help is appreciated.
Jeremy
Any idea what else it could be? I know there are relays in the fuse box under the hood for trailer turn signals. Is there a way to see if these are bad?
Any help is appreciated.
Jeremy
Terry
Thread Starter
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Freshman User
Joined: Jan 2002
Posts: 37
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From: Whitefish Bay, WI
Well I checked all the fuses, didn't find anything, took a ride to the Dairy Queen, came back home and tested the lights at the rear harness connector with the multimeter again and the turns worked. Hooked it up to the trailer this afternoon and the turns work...
So somewhere, something, wasn't lining up or some other mystery ailment... but in the end it works. Thanks to everyone for their assistance.
So somewhere, something, wasn't lining up or some other mystery ailment... but in the end it works. Thanks to everyone for their assistance.
Hotshot
Joined: Jul 2003
Posts: 12,177
Likes: 40
From: Newport, WA
Well I checked all the fuses, didn't find anything, took a ride to the Dairy Queen, came back home and tested the lights at the rear harness connector with the multimeter again and the turns worked. Hooked it up to the trailer this afternoon and the turns work...
So somewhere, something, wasn't lining up or some other mystery ailment... but in the end it works. Thanks to everyone for their assistance.
So somewhere, something, wasn't lining up or some other mystery ailment... but in the end it works. Thanks to everyone for their assistance.
