Seat Belt Dash warning light MK 2 Stag 1974

[RogerS]

Hi All

My dash warning light isn't working, never has since I got the car,as I understand the operation, you sit in, turn on the ignition and the warning light illuminates until one or both seat belts are engaged..Checked the bulb, all good, it has power, as when I ground out the holder behind the dash it works with ignition on. When I replace into the plastic dash block nothing as I have taken away the earth.

Can someone please tell me how this is wired as I cant find reference on my wiring diagram.

I assume under normal operation by inserting the belt buckle the unit takes away the power somehow, but how does it do it and how does it know if there is a passenger or not ? or does it just work on drivers side ? Baffled

Thanks

Rog

[trunt]

The circuit will be in the federal wiring diagram, there are switches in the seat belt clips, one in the passenger seat, a switch in the gearbox and finally a switch on the ignition lock (not the actual ignition switch). which only enables the buzzer for seats and doors.

l am looking at the federal diagram LE20272 on.

Power comes via the gearbox switch and goes to both seat belt switches. They both feed the lamp but the passenger side goes via the seat switch, The belt switches are normally closed, the seat switch normally open (but see note below) the other end of the lamp is grounded. so when the drivers belt is not secure the power is fed to the lamp. Also when someone is sitting in the passenger seat AND the belt is not secure the power is also sent to the lamp.
The switches also feed the buzzer via a diode. The buzzer is also fed from the interior lights by a diode, the diodes prevent the two circuits interfering eith each other. The buzzer is grounded by a switch that sits on the ignition lock.


Does the buzzer work? that can tell you something.. otherwise chase the circuit starting at the seat belt switches and check that the 12v is there from the gearbox switch. the gearbox switch uses that notoriously bad connector near the starter motor that also causes starting problems.

*note I have never seen this actually work, just reading the diagram.. e.g the cct does not show seat switch as normally open but thats what makes sense..otherwise the light would always be on if there was no passenger!

Hope that helps
Terry

[alan_thomas]

Roger first thing to check is whether you have the original seat belts. Most cars have had replacements by now. Without the original centre binnacle with the switches inside it’s a non starter.
you can replace the legand inside with anything, I’ve seen ‘Water Level’
- Alan

[new to this]

Roger

Under the drivers seat your find a switch ( its mounted on the rubber mat under seat) with two wires,dont think they had one on passengers seat but could be wrong, try shorting that out first to see if thats faulty, ignition must be on, also as Alan says if your seat belt bucket dosent have two sets of wires coming out it wont work

Dave

[mallardstag]

Roger

Under the drivers seat your find a switch ( its mounted on the rubber mat under seat) with two wires,dont think they had one on passengers seat but could be wrong, try shorting that out first to see if thats faulty, ignition must be on, also as Alan says if your seat belt bucket dosent have two sets of wires coming out it wont work

Dave

I think it's the other way around, switch under the passenger seat only as you can assume the driver will be present.

Here's the relevant section of the wiring diagram for RHD cars. I think the buzzer was only fitted to federal cars.

Annotation 2020-04-19 135702.jpg

[Ritchie6]

..otherwise the light would always be on if there was no passenger!

This is the problem I have but it doesn't really concern me too much. At least it doesn't have a buzzer constantly sounding which would be annoying.

Richard

[trunt]

This is the problem I have but it doesn't really concern me too much. At least it doesn't have a buzzer constantly sounding which would be annoying.

Richard

I deleted mine, buzzer and all!!

I have an over temp light from the EWP Controller for that spot on the dash..

Terry

[RogerS]

Hi

Wow ! great replies, thanks. Firstly I have the original belts and sockets in a carpeted pod between the seats, there is no buzzer that I am aware of. I guess I need to investigate the gearbox supply and any connections to the belt sockets and under the seats.Not had the car long, it is totally original as far as I can tell and this is the only thing that doesn't work so I would like to sort it if possible but not desperate.
Sounds like not an easy 5 min job, don't you just love classics LOL. Still got plenty of time on my hands at the moment..

Thanks

Rog

[trunt]

You probably do not have the gearbox switch, seems that’s only Federals.. also seems my description is totally opposite to the circuit mallardstag provided above, I.e. it’s grounding the lamp, not supplying it As per Federals so ignore my previous post!!

So find the LG/O wire at either of the seatbelt connectors and ground it.. light should come on.. If it does then something is wrong with the switches and the ground to them, if not then somethings wrong to the bulb or it’s supply.

Terry

[RogerS]

Just had a quick look under the seats, no wires drivers side but 2 wires going to a pad under the passenger seat, a dark green and a LG/ with orange tracer.How do I get the carpeted seat belt pod off between the seats ? I can slightly lift the front but it is fixed somehow at the rear. Don't want to break anything.

Thnaks

Rog

[trunt]

Take the ashtray out, there is a screw there and once that is out there are tabs that hold the front, so slide it back a bit to disengage the tabs, it should lift off.

[RogerS]

Hi Terry

Wires all present under the Pod, I grounded out the LG/O and the light came on, so I need to look at the switches I assume you mean the belt receivers ?

Thanks

Rog

[trunt]

Yes, remember the Passenger side also goes via the seat switch.. have you sat SWMBO in there and did the light come on?..

Just put an ohmeter across the seatbelt switches at the plugs, that will tell you if they are working.. should be short with no belt secured, open when belts clicked in..

Terry

[RogerS]

Hi Terry

Put the meter across the switch plugs and both are dud, sealed units so cant get in there to see whats going on. Not to worry, not going to loose sleep over it.

Thanks all.

Rog