Lucas 6RA 33247b electric window lift relay, Jaguar 420G

Guys, having issue with my window lift relay. When I press window switch, window motor runs for a few seconds, then a click comes from the relay and window stops. After several seconds, relay clicks again and windows lift runs for a few second until next click… I wanted to go through the easiest solution. I have two same relays, but both do the same. So I wanted to buy a new relay, but… I cant find any mention of this type of relay anywhere. Its Lucas 6RA 12V 33247b relay, with W1, C2 and C3 contacts… Can anyone advise me? Any relay replacement? Or if both used relays do the same, is the error somewhere else than in those relays?! As theres also a windows lift circuit breaker (Klixon) and another window lift relay (Lucas 9RA 33234) connected… IMG_20201205_002656|375x500

I have a chart somewhere, and the info is on the Internet, how to wire a standard Bosch relay to do the same job as various Lucas relays

I would try this first, especially if is a hidden relay

In addition, if the fault is replicated with 3 separate Lucas relays, I would suspect some other fault. I have an idea these individual window motors have a thermal cutout

It’s not the relay, it’s the thermal switch. Klixon. Check there.
Does it happen with all windows?

That will be helpful, thanks. I was thinking of buying a different Lucas relay were w1, c2 and C3 slots are present together with some other slots, but im not sure, if that work or not… Have to read more about these relays… Until now, 2 used relays are faulty, so that was the reason i intended to give a chance to a new relay…

Ah, ok, thanks, yes, happens with all 4 windows. I have 2 complete used sets of this window electric instruments but the problem remains no matter how i combined them together…

I would trace the power with a test lamp or multimeter, but this would make sense:
The relay is switching, as you can hear, and provides power because the motors run.
Something switches the relay off.
The klixon switch is what can the relay turn off and on. Either it’s faulty or there is a high load somewhere in the circuit, maybe not the motors since it happens with all four.

I was thinking of a high load too, but where from? On the one side, the window lift relay leads to a fuse 8 and battery terminal post, on the other side, just windows switches and motors, which all cause the same. I tried both used klixon switches too with no difference. Its true, that I suspect relays because of “click” noise, but as you wrote, in fact, that could means quite the opposite, relay is fully functional. I also go around with multimeter with igniton on, but without pushing the switches… So Ill try to focuse on klixon now… Thanks a lot for your advices.
EDIT: Looking at the diagram just now, I realised that all switches and motors are connected with klixon through the RH front window lift master switch…so possible source of a failrue? Ill check that too…

Btw, anyone know where to get a new klixon? :smiley:

This is one of the few pieces of a 420G that I am completely unfamiliar with (although I do have some power doors off a wreck)

Without looking at any documentation, if the device is merely a “thermistor” that works with a relay, they can be bought individually, and are like a diode, with a Temp and Current rating, if they get too hot, they cutout

Guys, thanks for your advices and “brainstorming.” As I read a bit more about it, David is probably right, I suspect the brake circuit device now. Faulty brake circuit device should cause “slow movement of window and need of switch beeing pressed several times to open/close window.” Thats exactly my case… so Ill continue to search for some kind of replacement and let you know the result, when there is some…

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I don’t know about 420Gs, and I can’t find any reference to a Lucas 33247B, but I know a bit about 1960’s auto electrics. That image doesn’t look like a “thermal protector” (in modern terms an “auto-reset circuit breaker”). It looks much more like what they used to call a “horn relay”. A horn relay is a 3 terminal relay:

  1. A common power feed to both a contact and the winding.
  2. The other side of the winding which is typically switched to ground.
  3. The other NO contact to the load.

The best way to be sure is to check the schematic.

That 33247B form and fit is virtually identical to a 1960s Delco horn relay. They are still available. Finding one in Europe might take some work.


Hi Ron. Many thanks for your involvment. Regarding electric windows, there are two Lucas relays - one of them is Lucas threepoint horn relay, youre right. But theres also Klixon thermo switch. See attached diagram and complete pic.

Regarding replacement relay. I can find some relay, that have C1, C2, C3, W1, W2 connections, but from 4 - 8 connection points. Im not sure if I can use them or not, I do not have that 33247B relay schema, so I just guess, if its enough to be led just by connector mark? So is the C1 point (and all others) same on every Lucas relay? I suppose internal scheme varies, but I dont know…

Regarding Klixon - if I understood that right, there are plenty of new Klixon switches available and, in fact, its just an “automatically renewal fuse.” So as window circuit is under 50A fuse (i guess just now), In my opinion should be totaly fine to buy a new Klixon 50A switch…

But to be honest, Im overloaded with my office job duties right now, so I did not red about that as many articles as I would like to…I also read an electrical schoolbok from 1970s when I have a bit of time through the night… But finally, Im beeing suspicious, that maybe Klixon switch is fine too and failures are caused by overloading because of that rusty connections? Or maybe stuffy window mechaism? Wiring itslef seems to be fine when checked with multimeter with ignition on… Unfortunatelly I do not have a time to get to the garage till this weekend, so I plann to make more searches and attempts just in a few days…

Ill be glad to hear your opinion.

Be safe



somewhere I have a comprehensive list of many more Lucas relays

cant find it atm, due to a computer change

perhaps this will be helpful

The schematic is very interesting, enlightening, and has some surprises. I’m 98% sure that I see the theory of operation. Normally, something (probably ignition switch) provides power to the 33247B relay and klixon circuit breaker. The relay is in the quiescent (non-operated) state. Power feeds through to the window switches. When a switch is thrown the motor operates. When the motor gets to the window limit, the motor is stalled. The stalled motor draws high current, which causes the voltage at W1 to go very low, which causes the 33247B to operate, which causes the circuit to open. I suspect the klixon circuit breaker is sized to trip somewhere between normal operating current and stall current to protect against motor overload from a sticky window. During a stall, the klixon does not trip because it is much slower to react than the relay. There are other interesting tricks in this circuit, but I’ve bored everyone enough for now.

It’s always worth cleaning up the connections and tracing the voltage with meter.

Unfortunately, the schematic clearly shows that the 33247B is not a typical horn relay. It’s backwards. It’s like a horn relay but the contacts are NC instead of the typical NO. That’s ultra-rare. If the relay proves to be unusable, my non-concourse suggestion with be to use a common 6RA Lucas SRB146 instead. On the SBR146, you need to jumper C2 to W2 and then connect C2, C3, W1 same as the 33247B.

Good luck,

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So, still have no time to practice, but spent a bit of time in theory… And maybe this will help to someone too. In theory, my instrumemts seems to work just fine and i should start with the easiest solutions ať first… Lubricate my windows mechanism is my first choice, as my JAG is more or less a barn find…

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Yeah. Sounds like a good idea to start with the mechanics. You might lucky and not have a serious electrical problem.

I’ve got a similar problem with the sunroof on one of my non-Jag vehicles. The motor seizes and will pop the break if stay on it for more than a couple seconds. Unfortunately, it’s a big job that requires removing the headliner. So… it’s going wait until I have more time.

Good luck,

Thanks, Ill let know the result later on…

So, out of the doors, without any load, motor and mechanism runs perfect. Ill try to clean and lubricate everything, upper doors and window sealing included and well see…

Ron has described how the system works very well and you have confirmed that by running the winder motor with no load and seeing no faults in operation. It sounds like everything needs to be cleaned, lubricated or adjusted so the windows don’t push into a bowed out door sill, if that is what is causing the strain on the motor.

Lucas relays have a common nomenclature so you can mimic the effect of the “rare” relay by using a standard 6ra 5pole changeover relay (which has all of the w1,w2 and c1-3 connections) and connecting the relevant pairs together whilst leaving the unwanted ones disconnected from your loom.

kind regards

Yes, regarding electric windows, its the best possible option, so lets hope. Id like to manage at least part of the windows through the christmas hollidays. Also thank you for your tip with a lucas relays, maybe Im going to buy a new general one just to try your tip in practice… Thank you for your advices.

Hi guys. So, after 5 months, i finally find some time to do the job :smiley: And yes, just made a proper clean of mechanism, door frame, and a motor itself and voila, problem disappeared. So, maybe its handy information for someone later on… Thank you all!