Thermal cutout?

[Robbie693]

Does anyone know where this is located and what it looks like?

The only thing I can find behind the dash (without removing it) that may be it is a bakelight looking strip thing with wires going to it that is screwed to the pasenger side of the heater... Is this it?

[john.p.clegg]

That "thingy" is the fan rheostat and gives you the three speeds of operation...
John

[john.p.clegg]

Which "thermal cutout" are you looking for???
John

[Robbie693]

Oh right, thanks John.

I'm looking for the thermal cutout for the headlights. I've got the 'all lights go out after 10 or 15 minutes use' problem...

[tdafforn]

Your lucky you get 15mins...
I get 15 secs!
I think the cutout is screwed to the dash on the lhs by the cigar lighter..
Cheers
Tim

[Matt]

Hi Robbie

Mine was mounted next to the light switch, its a small black plastic unit with a bimetallic switch in (see arrow) you got an S130 yeah ?

[Robbie693]

Nice one Matt! Great help, I'll have a look at mine. Yes mine's an S130.

Cheers

Can these be bought new?

[Hamish Coutts]

Guys,

The problem is that the current consumed by the headlights is near the tolerance limit of the cut out. Even fitting a set of uprated instrument lamps can do this. (i.e. 4w instead of 2w)
I had this problem when I fitted uprated headlight lamps. What an eejit I was. Headlights cut out pretty quickly and as luck would have it, going into a corned in the pitch dark! A bit concerning to say the least. (I had uprated the wiring BTW).

Fitted a couple of relays to do the switching for me. Now the cut out only sees the far smaller current used by the relay coils. Problem solved.

Hamish.

[alaric]

Surely a device that can turn off your headlights without any warning is really bad. Is it there to prevent fire? If so, isn't that actually a very dangerous bodge? The relay solution sounds like a sensible upgrade, and if fitted to supply current from a low impedance path to the battery will probably give you much brighter headlights than changing bulbs over.

Sean.

[Matt]

I replaced mine with an inline fuse

Having my headlamps go out when doing high speed night driving, scared me rather !

I've been using my 10 amp fuse fine with no failures or fires

[Robbie693]

I've read about doing the Relay thing but I'm an electrical dunce. Anyone fancy putting an idiots guide to doing it up?

Stuff like what wire to use, type of relays, where to connect etc...

[denicholls2]

While putting the headlights on a relay is a good idea, I suspect your problem is either:

1. Loose connection.
2. Use of higher-amperage than design components.

A loose connection adds to the current draw of the circuit by wasting energy in arcing the loose gap. The headlights will be brighter at less current draw with good connections.

Remember also that whatever the cutout did will be pretty much completely defeated by a relay system. Not that this is a bad thing...

The simple concept of the relay is to bring the hot power as close as possible to the headlights before switching it. A heavy guage wire runs to somewhere between the headlights, another heavy guage wire runs to the headlights, and a relay is used to make the connection between the two. This relay needs to be suitable for the current draw of the components, and you need two circuits on the headlamp side only, one each for low and high beam. The original circuit (absent connection to the headlamps) can then be used to activate the relay (and taillamps and running lights).

Note that if not done carefully, this will have the negative effect of creating an unswitched source of hot power for short circuits and the ensuing electrical fires near the headlights. No lamp cord, please!

[simonriley11]

If you want a new cutout I got mine from Paul Matty. Having said that I've not driven the car in the dark since the lights cut out on me (very scary indeed) so the idea of an in line fuse to replace the cut out sounds pretty good to me.

[Robbie693]

Thanks Simon, I had heard they can be bought new, although I also heard they were quite expensive...?

I'll check the circuit first and see if I can find any weak spots, and see what the headlight bulb rating is. If that's all ok then I may use Matt's suggestion of a fuse.

How do you work out the appropriate rating?

[simonriley11]

Robbie, from my 'O' level physics (taken a very long time ago) I think the equation is Power(in watts)=Voltage(in volts) X Current(in amps). So therefore if the lights take 96 watts(for example) then with 12 volts the current draw would be 8 amps. I'm sure some of our fellow 'forumers' will be able to more detail as to how much allowance should be made and what the true power consumption of the lights is etc. Another thought might be to look in the workshop manual for earlier cars which I believe didn't have the thermal cutout and see what fuses were used in their case.