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Do 72-78 d or w series trucks have a factory horn relay?
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Author:  Greg Ondayko [ Thu Feb 01, 2018 6:18 pm ]
Post subject:  Do 72-78 d or w series trucks have a factory horn relay?
Do 72-78 d or w series trucks have a factory horn relay?


Greg
Author:  DadTruck [ Fri Feb 02, 2018 6:33 am ]
Post subject:  Re: Do 72-78 d or w series trucks have a factory horn relay?
Greg, my 83 D150 has a relay in the horn electrical circuit, it is located on the fuse panel.
Relays are not new technology, so I am thinking that 70’s vehicles would have them.
Author:  wjajr [ Fri Feb 02, 2018 6:50 am ]
Post subject:  Re: Do 72-78 d or w series trucks have a factory horn relay?
Its got to have a relay somewhere.
Author:  Charrlie_S [ Fri Feb 02, 2018 7:35 am ]
Post subject:  Re: Do 72-78 d or w series trucks have a factory horn relay?
No relay.
Horns get fed 12 volts (circuit F-15 LG/B wire) from the fuse block (horn/back up lite). The other wire (circuit H-10 DG/W wire) on the horn gets grounded by the horn switch in the steering wheel. This is from the 1977 Truck service manual.
Author:  SlantSixDan [ Fri Feb 02, 2018 11:18 am ]
Post subject:  Re: Do 72-78 d or w series trucks have a factory horn relay?
Holy carp, if there's no horn relay that is some seriously negligent engineering on Chrysler's part. Horns draw a lot of current; it would be foolhardy and dangerous to have that much power going up and down the steering column and through the light-duty horn switch.

I note there is a horn relay shown for a '77 D150 in all the aftermarket parts cattledogs I check, but I don't have a Dodge Truck FPC in the '72-'78 year range to check.
Author:  Charrlie_S [ Fri Feb 02, 2018 12:34 pm ]
Post subject:  Re: Do 72-78 d or w series trucks have a factory horn relay?
I submit the parts catalogs are incorrect. I double checked my 1977 factory service manual, all models of dodge truck, from 100 series to 800 series. No relay. Did find something interesting, 1977 D700, D800, and S700 had electric anti skid system.
PS This is the only rear wheel drive manual, I have.
Author:  Greg Ondayko [ Fri Feb 02, 2018 1:57 pm ]
Post subject:  Re: Do 72-78 d or w series trucks have a factory horn relay?
Cool,

Thanks for the info. My truck is pretty much stock, not messed with etc. And has no relay.

Tech at PA insp. Was questioning it


Horn will not work without engine running due to current draw and no relay.

I might add one.

Greg
Author:  Charrlie_S [ Fri Feb 02, 2018 4:00 pm ]
Post subject:  Re: Do 72-78 d or w series trucks have a factory horn relay?
Really easy to add a relay. All wireing changes can be done right near the horns.
Disconnect the LG/BK wire from the horns. Connect it to the relay coil and one contact. Connect the other contact to the horns. Disconnect the DG/WH wire from the horn, and connect it to the other relay coil terminal. Connect a ground wire to the horn terminal that did have the DG/WH wire you removed. Done.
Author:  Reed [ Fri Feb 02, 2018 6:39 pm ]
Post subject:  Re: Do 72-78 d or w series trucks have a factory horn relay?
FYI- I recently had the opportunity to look at a factory wiring diagram for a 1974 Dodge van precisely to see if there was a horn relay. Answer- no horn relay. Very odd and surprising that there was a full currently flow through the steering column.
Author:  Rick Covalt [ Sat Feb 03, 2018 5:37 pm ]
Post subject:  Re: Do 72-78 d or w series trucks have a factory horn relay?
They saved 16 cents that way!! :?
Author:  Pierre [ Sun Feb 04, 2018 7:40 pm ]
Post subject:  Re: Do 72-78 d or w series trucks have a factory horn relay?
Quote:
Connect it to the relay coil and one contact.
Doesn't this defeat the purpose of the relay? If I read this right the horn will still be sourcing current from the original wire. The original horn wire should only feed the coil. One side of the normally open contact to the horn, the other fused directly to the battery.
Quote:
Horn will not work without engine running due to current draw and no relay.
Engine running or not shouldn't matter, the battery has plenty of current to power a horn on it's own without the alternator. Just like how headlights should work without the engine running as well. If the harness itself was the limitation you would have trouble regardless. Sounds like there are other electrical issues here - maybe the horn circuit was somehow moved from the "always hot" side to the "hot with key on only" side.
Author:  Charrlie_S [ Mon Feb 05, 2018 5:55 am ]
Post subject:  Re: Do 72-78 d or w series trucks have a factory horn relay?
Quote:
Quote:
Connect it to the relay coil and one contact.
Doesn't this defeat the purpose of the relay? If I read this right the horn will still be sourcing current from the original wire. The original horn wire should only feed the coil. One side of the normally open contact to the horn, the other fused directly to the battery.
Partially. The feed wire from the fuse box, will still handle the same amount of current, but the wire that goes back to the steering columm, and horn contacts, will not have high current, just the relay coil current.

Another way to wire would be to connect the LG/BK wire from the fuse box to just the relay coil, and add a fused wire from a 12 v source in the engine compartment ( starter relay, batt, etc). All other connections the same as my other post.
Author:  TenTea [ Wed Jul 11, 2018 11:16 am ]
Post subject:  Re: Do 72-78 d or w series trucks have a factory horn relay?
Just unwrapped my wiring harness at the big firewall plug last night and was looking at FSM wiring diagrams trying to cipher the proper wire to power my horn. Should be simple, right?
It's sitting there, well mounted, but all lonesome on the inner fender, and with no likely suspects to power it, nearby.
I hope to get it connected and working tonight.
The horn wiring in the steering wheel looked good when I replaced the turn signal assembly so I'm confident in that end of things.
I thought I was looking for a dark green wire with red trace but did not find such an animal and there were several shades of *green wire* to look at...
Author:  Greg Ondayko [ Mon Jul 16, 2018 7:29 am ]
Post subject:  Re: Do 72-78 d or w series trucks have a factory horn relay?
by 1984 there might be a relay and possibly the factory location of the horn is different.

my 77 has them in front right by the hood release.

Greg
Author:  Greg Ondayko [ Mon Jul 16, 2018 7:31 am ]
Post subject:  Re: Do 72-78 d or w series trucks have a factory horn relay?
Quote:
Quote:
Horn will not work without engine running due to current draw and no relay.
Engine running or not shouldn't matter, the battery has plenty of current to power a horn on it's own without the alternator.
Yes that is the conventional thinking.. but it just dosen't work - with the engine running it beeps fine.

It tries to beep without the engine running but just makes barely audible groan and clicking sounds.


Greg
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