Hazard Switch

[AdamQ]

As part of my rebuild, I've naively/ambitiously gone for some LED push-button switches in place of the standard rocker switches; apart from the blues for the lights being out of stock I think I've almost cracked it with the exception of the hazard switch - getting a standard latching switch to do what the rocker switch does is going to be a bit like doing heart surgery with a butter knife as far as I can tell - thought I'd found a cunning electrical gizmo from CBS but it's just a plastic mechanical botch that won't work with my switches.

Apart from keeping a red flag and an orange triangle in the boot does anybody have any suggestions?

Many thanks,

Adam

[revilla]

Hi Adam,

Looking at the wiring diagram you would effectively need 3 standard automotive relays to replace the hazard switch. One changeover type and two simple on-off (normally off) types. Or you buy a single 12V "3PDT" relay, which is basically three changeover relays built into one.

This is the wiring diagram for the switch:

You could replace it with a 3PDT relay as follows:

Please excuse the rushed reply and scribbled diagram!

You would then arrange the new hazard switch to just switch the relay on. The LED in the switch would be wired in place of the bulb in the above (assuming it's a 12V LED, if not you would need a resistor in series).

If you wanted to use standard automotive 4 and 5 pin relays, just replace each of the three sections above with a relay and wire all the relay coils in parallel.

Drop me a BM if you want any help, parts, instructions or whatever.

[AdamQ]

Fantastic!  To my very limited understanding of these things, that looks like the perfect solution ...  Thank you!

Whilst I have your attention, could I beg your help with the wipers and lights (I sort of think I've got them sorted but ...).  I'm replacing the Off-On-On rocker switch in each case with two latching Off-On switches (one for slow wipers/sidelights and the other for fast wipers/main beam) - might you be able to do one of your idiots' guides as above for those?

Eternally grateful ...

Adam

[revilla]

The wipers are a bit more complicated because of the self parking feature. I did some diagrams for them for somebody else recently. I'll BM you my email address; if you could drop me an email with a bit more detail on what Switches you've got and what you're trying to achieve it will act as a reminder. It might take me a bit to get back to you as work is a bit crazy right now. I'll try to post my suggestions back on here for future reference.

[elie boone]

CBS does a push button hazard switch, I used a toggle switch for the wipers first speed, and another toggle switch for the intermediate swipe, the self parking is just an external + feed.

[revilla]

There's an excellent writeup of the full workings of the wiper system at http://www.mgb-stuff.org.uk/wiper3.htm - the Caterham system is identical in operation but uses different wire colours.

The self parking system should be more than just a postive feed. As described in that article, the internal parking switch is designed to short circuit the motor windings when the park position is reached. This acts as an electromagnetic brake which stops the motor dead and stops it running on a bit due to inertia when the power is removed, leaving the wipers not quite parked in the right position. This requires one pole of the switch to be a changeover type, as the connection which is made when the switch is off is used by the parking system.

Pinching one of the diagrams from that article:

http://www.mgbimages.uk.gridhosted.co.uk/images/wiper4d.jpg

You will see that in the "Off" position (as shown), power (Switch Pin 4) is not connected to either the low speed (Switch Pin 6) or high speed (Switch Pin 8) motor winding, but the low speed motor winding (Switch Pin 6) is connected through to Pin 2, which is fed with power by the parking switch in the motor until the parking position is reached, then shorted to ground. This shorts across the low speed motor windings, dumping the energy in the spinning motor to ensure accurate parking.

So the connections made by the switch are:

Off: Pin 2 to Pin 6
Low: Pin 4 to Pin 6
High: Pin 4 to Pin 8

As I understand it, you want to replace the switch with two simple SPST On/Off switches, one for "Wipers On/Off" and one for "Wipers High/Low". You can get very close to this using two standard automotive 5-Pin (changeover) relays as shown below (I've labelled the sketch with the Caterham wire colours used):

So the first relay is operated when the "Wipers On/Off" switch is "On" and the second relay is operated when the "Wipers High/Low" switch is "High". You will see that the connections made by these relays are as follows:

Off/Low: Pin 2 to Pin 6
Off/High: Pin 2 to Pin 8
On/Low: Pin 4 to Pin 6
On/High: Pin 4 to Pin 8

The only one of these which is different to the original configuration is the combination "Off/High" which the original switch simply doesn't allow you to select. However, looking what this would do, it would simply mean that if you switched the wipers off when running at the higher speed they would continue to run at higher speed to the parking position and the high speed winding of the motor would be shorted to brake them; they may not park quite as accurately but other than that, all would be fine.

Because this simulates the original switch connections, it would work fine with the intermittent wipe you have installed, with a brief selection of "On" putting the wipers into intermittent mode - at least with the "Low" speed selected, I'm not sure if the electronics would recognise a brief pulse on the high speed wire or not. So you may need to have "Low" selected to be able to trigger intermittent.

Andrew

[elie boone]

For sure on any car modern or old a brief pulse is enough to have the wipers do 1 sweep ( done manually ) you could use a ON/OFF/ON switch for the wipers

[revilla]

I think from what he tells me that Adam's car has the Lucas 6DA (or the compatible Caterham replacement unit) electronic intermittent wiper controller system installed (as does my car). In this case a brief pulse of the wiper switch activates the intermittent delayed wipe function and the wipers then continue to sweep about once every six seconds automatically without the driver having to do anything, under the control of the electronic unit. Another brief pulse disables intermittent mode.

My comments were referring to whether the 6DA would respond correctly to the brief pulse when the speed switch was set to "High", rather than whether a brief pulse would trigger a single wipe through the parking system.

I think he has already chosen the switches he wants to use as well, which are simple latching single pole single throw 3A rated push buttons https://www.switchelectronics.co.uk/switches/push-button-switches/vandal-resistant-switches/vandal-resistant-illuminated-16mm-switches/green-angel-eye-16mm-latching-switch-12v-spst.

[elie boone]

OK, I use a Ford intermittent relay for the wipers hence the other interpretation

[AdamQ]

Hi Andrew,

Once again, fantastic!  Just the sort of fool-proof guidance this electrical dope needs - can't thank you enough for your time and effort in providing such a comprehensive solution and the instructions to effect it ...

I've ordered the various parts required and, for once (I usually dread it), I am looking forward to a bit of cutting, crimping and heat-shrinking ...

Thanks again,

Adam

[AdamQ]

Just to say that I've now implemented the circuits/arrangements detailed above by Andrew and both hazards and wipers worked first time without a hitch.

I used this from eBay for the hazards:

https://www.ebay.co.uk/itm/sourcingmap-JQX-10F-3Z-DC-12V-Coil-Voltage-3PDT-Power-Relay-10A-w-Socket/182614789354?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

Here's the diagram above with the terminal numbers on the 3PDT relay mapped across:

and here it is in situ (with the relays for the wipers mounted beside it):

A final vote of thanks to Andrew for yet another set of faultless instructions.

Adam

[revilla]

Adam,

 

Glad to hear it all worked first time. Looks neat enough installed too!

 

Andrew