HD headlight harness issues
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Laughing Gas
Joined: Jan 2023
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HD headlight harness issues
I have a 1988 f150 xlt lariat. I went to install an upgraded headlight harness. It works low beam but not high beam. The old headlight plug was plugged into the new harness, both bulbs were plugged into the new harness, each bulbs ground was connected. The 12v was connected, the relays work I switched them around and it’s still being weird. It doesn’t work one moment with the high beam the next it stays the same as the low beam. I will upload a picture of the instructions when I have a chance.
Lead Driver
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I have a 1988 f150 xlt lariat. I went to install an upgraded headlight harness. It works low beam but not high beam. The old headlight plug was plugged into the new harness, both bulbs were plugged into the new harness, each bulbs ground was connected. The 12v was connected, the relays work I switched them around and it’s still being weird. It doesn’t work one moment with the high beam the next it stays the same as the low beam. I will upload a picture of the instructions when I have a chance.
Lead Driver
Joined: May 2009
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From: Tobyhanma, PA
Seeing the directions and how you worked it up might help. Could be something simple.
Switch could have gone bad as mentioned too. Could always unplug the new harness amd plug the bulb back in to check that pretty quickly tho
Switch could have gone bad as mentioned too. Could always unplug the new harness amd plug the bulb back in to check that pretty quickly tho
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Laughing Gas
Joined: Jan 2023
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I took the HD back out for now. When I get back to the house I will upload a picture of the HD harness wiring diagram/instructions. I will check the dimmer switch works as well. But I’m 99.99% positive it does, it shows on the cluster the brights are on. And I used the brights a few days ago.
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Laughing Gas
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Lead Driver
Joined: May 2009
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From: Tobyhanma, PA
I could read them both. Very similar setup to what I've used before on other vehicles. Heck got one on this truck too, can't remember brand though.
So you hooked it up per the diagram and don't have high beams. Itdnpossible the relay isn't seated in their harness all the way, or it could be bad.
Could swap the two relays and see if you get only high beams. Or you could use a multimeter to verify voltage at the appropriate terminals, should be 87 or 87a can't remember which a 4 pin has vs a 5 pin
If everything checks out on the harness and relay side then I'd look at the bulbs. They may have been fine last week or so, but everything works one time and not the next at some point.
So you hooked it up per the diagram and don't have high beams. Itdnpossible the relay isn't seated in their harness all the way, or it could be bad.
Could swap the two relays and see if you get only high beams. Or you could use a multimeter to verify voltage at the appropriate terminals, should be 87 or 87a can't remember which a 4 pin has vs a 5 pin
If everything checks out on the harness and relay side then I'd look at the bulbs. They may have been fine last week or so, but everything works one time and not the next at some point.
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Logistics Pro
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From: Chillicothe
If you followed the directions then they should work.
Unless there is a bad relay.
Or a bad connection at a socket the relay plugs into.
Use a multimeter to check power at the high beam socket. I had a similar problem a month ago when it got stupid cold here. Highs worked fine at dusk on the way to a buddies house. Four hours later lows worked but no highs. Not a big deal got down the road about 10 miles and tried again nothing at first then "CLICK" I had highs. It got so cold that evening that the relay froze. So I replaced it, had a little moisture in it so it would happen again.
Unless there is a bad relay.
Or a bad connection at a socket the relay plugs into.
Use a multimeter to check power at the high beam socket. I had a similar problem a month ago when it got stupid cold here. Highs worked fine at dusk on the way to a buddies house. Four hours later lows worked but no highs. Not a big deal got down the road about 10 miles and tried again nothing at first then "CLICK" I had highs. It got so cold that evening that the relay froze. So I replaced it, had a little moisture in it so it would happen again.
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Laughing Gas
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I did some testing with someone today on the harness. Everything has power, everything has ground, and everything has continuity. So we plugged it all in but we left the drivers side headlight unplugged from the new harness, and we turned the headlights on and actuated it, which it actuated but backwards high beam was low beam and low beam was high beam. So we plugged the drivers in and then the low beam worked and the high beam shut the headlights off, and I unplugged the drivers, and then it still shut off when high beam was on. The relays do actuate I can hear them click if I unplug and plug them in. The thing is I noticed if I unplug either relay the headlights dim, so I think the low beam is high and then when I hit the dimmer switch it shuts them off. The HD harness is taken out of the truck right now, everything on the factory works, bulbs, dimmer switch, and headlight switch. I swapped relays no change. I’m thinking defective harness?
Lead Driver
Joined: May 2009
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From: Tobyhanma, PA
Something off there for sure. It sounds like a bad connection somewhere. Either a bad ground or a crimp internal to the harness isn't solid.
Unplugging one relay shouldn't affect the other.
Unplugging one relay shouldn't affect the other.
Cargo Master
Joined: Mar 2003
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You mentioned drivers.
Do you have some of those cheap Ebay euro/projector/crap lights or similar?
Not that it should matter if hooked up per diagram and if they worked before but you never know. Make sure that the original harness hadn't been modified for any aftermarket lights
Do you have some of those cheap Ebay euro/projector/crap lights or similar?
Not that it should matter if hooked up per diagram and if they worked before but you never know. Make sure that the original harness hadn't been modified for any aftermarket lights
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Laughing Gas
Joined: Jan 2023
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I don’t believe it’s been modified I’ll double check. It’s the nice $50 sylvania bulbs I got the best ones they sold for my truck.
https://www.autozone.com/collision-body-parts-and-hardware/headlight/p/silverstar-ultra-headlight-and-fog-light-bulb-9004su-2/862294_0_0?searchText=Headlight
I believe these were what I got.
Housings factory it has a ford logo
https://www.autozone.com/collision-body-parts-and-hardware/headlight/p/silverstar-ultra-headlight-and-fog-light-bulb-9004su-2/862294_0_0?searchText=Headlight
I believe these were what I got.
Housings factory it has a ford logo
Lead Driver
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I don’t believe it’s been modified I’ll double check. It’s the nice $50 sylvania bulbs I got the best ones they sold for my truck.
https://www.autozone.com/collision-b...Text=Headlight
I believe these were what I got.
Housings factory it has a ford logo
https://www.autozone.com/collision-b...Text=Headlight
I believe these were what I got.
Housings factory it has a ford logo
your truck uses 9007
This is your problem most likely
" The 9007 has the ground pin in the middle, and high/low positive pins on the outside. The 9004 has the ground pin on one side, and in the middle and other side are the positive pins for high beam and low beam."