I have a 4 pin relay on my 73 Duster, is the separate pin for the door buzzer ?
TIA Mick

Looks like that fourth wire, black, goes to the left door switch

A link to the wiring diagrams in case you don;t have it. I used 73 Valiant since the Duster is based off the Valiant.

all 71/73 Mopars got the 4th prong for the KEY IN buzzer as standard equipment integrated on horn relay. Not a door buzzer, but only buzz when key is in and DRIVER'S door is opened. Since 74 was a separated buzzer controled by the interlock brain box

The wiring diagram shows a single black wire on the single pin but mine has a double blue wire on it and my meter shows continuity with one end on there and the other on the horn wire but when I connect it to the relay the horn is making a closed circuit without pressing the button.
Mick

Been looking through the diagrams on my mopar and the 76 shows blue wire coming off the single pin, my 73 has two blue into one connector.

have no idea what you talk about.

Blue wires are on 73s ( practically on all cars ) for RUN circuit which, inside the cab, feeds the seatbelt warning system too ( buzzer and lights ) since turns on when you put the key in RUN. Sooo you must be looking at something else.

Driver side door jam switch must get a yellow wire for dome light and black wire for warning buzzer systems. Passenger side just yellow.

I can be missing something because I'm thinking based on what I recall and my B body gets. However I don't think A body or any other body is way diff and my memory uses to be good

If you look at the 73 diagram i've attached, there's a black wire on the fourth pin, mine has 2 blues into one connector.
Mike

Could I utilise one of the 3 pin relays I already have, if I split the wires ?

well... must be a single black wire. My uncle's 73 Dart got a single black wire there.

Blue wire could be for some accesorie around, in your case, maybe seatbelt buzzer system. Search for a black wire with female terminal hanging around without use and plug it there.

The black wire arriving must be just the ground coming from ign key sensor, which on column is one of the reds for this switch.



The other red comes from door jam switch ground ( also black on underdash harness )

I hear you but my multimeter, sounded the horn wire to the blue connecter. The old relay was faulty, so I tried a 3 pin relay I had and it's buzzing continously, even with the horn wire not grounded.

Well, that wrong! The 4th pin must not affect the horn function since is just dedicated to the key in buzzer when driver side door gets opened.

Runs like this:
Violet... batt power from fuse box
Green traced red... horn signal ( positive ) when horn is triggered at steering wheel
Black grouped on the 3 group prongs... ground signal from horn switch. It comes from turning switch plug
Black separated prong... ground signal from key in switch sensor, which cames at the same time from door jam switch. When both switches are closed ( open driver's door and key inserted ) the buzzer gets the ground circuit for it closed and buzzes.

That is what must be. Nothing else.

I had a 72 Swinger who's wiring did not match the FSM and it wasn't messed with by some PO either.

The FSM was just wrong.

It was a late year build and it is possible that it wasn't reflected in the FSM, which is generally out early in the MY.

However, I checked all the wiring diagrams for all later years on that site and they all show the same setup. So, I dunno

Can't tell whatever diagrams and FSM says, but what really makes it work.

on a side, I never trust completelly on diagrams posted at MyMopars.com. They work as a guide but they are not perfect. They forgot about interlock system on all 74 models and never say anything about accesories

THIS is the setup on 71/73 Mopars ( I made the diagram quite ago )

Thanks for your replies, when I connect the violet and the green tracer to the relay it continually buzzes, even without the horn button wire ?



















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