How can I fit a warning light to a Retro temperature gauge?

you need two different switches, one would be a radiator fan switch, or thermoswitch, usually fitted in the top of the radiator near the top hose, so that adapter you've found to go in the hose will work fine.

these can be run direct, but for longevity its wiser to run a relay, you can run them two speed as well, don't get one too low a speed or it will be running all the time, and the engine will never get to a decent operating temperature.

the second would be a high temp warning switch, very simple device, usually just pull a voltage to earth once a certain temperature is reached, this will be higher than the fan cut in point

Some thickwall alloy tube could be cheaply tapped for a sensor switch possibly
Also i remember my old volvo 340 had a circuit board in the gauge that staged the warning light, solid red was hot, then it started flashing when it went nuclear so maybe more common volvo 700s etc have similar circuitry that could be adapted to run a seperate led bulb grafted in elsewhere

£20
www.burtonpower.com/parts-by-category/cooling-system/electric-fan-controllers.html

£15
www.extreme4x4.co.uk/acatalog/HOSE_ADAPTER_FOR_RADIATOR_FAN_SWITCH.html

Judging is not yet over but bortaf is in first place so far
(many thanks - they look ideal and are cheap functional rather than expensive bling )

Other info :
It's a Beastie not a Beetle (easy mistake so thanks for that )
Radiator drain is too small to fit a sensor (5 mm ish) but it's a good idea.
Thickwall tubing would work fine if I had an offcut but I'm a bit too hectic to go scavenging. Maybe next time...
The Volvo 340/700 info is good to know, but see above (too hectic etc)

The ideas are all appreciated - Bortaf has given me a solution but there's still time for other/different ideas.

Virtual beer tokens have been sent and should be with you shortly!

You could do both with Klixon surface mount stats - they are about £3 each on ebay and avaialable in many different settings and will carry current to operate a relay for a fan or a warning lamp. You could use two of them with two relays in a fan control circuit. T1 on T2 off.

The surface mounts could be fitted on the rad inlets or outlets depending on how you set them up if you used say 85 95 105 you could have a fan off at 85 fan on at 95 and warning lamp at 105 all for £20 and bit of wiring savvy.

The 95 would energise a relay with a latch and the 85 would remove the latch.

I fitted this to my Marina some years ago. It switches the fan on and could easily run a light in the dashboard as well.



FAE supply all sorts of radiator fan switches of different threads and temperature switch points to suit your engine. They do single fan and twin fan switches where the second fan is switched in if the temperature continues to rise.

This is their .pdf catalogue go to section 3 Radiator Fan Switches

www.fae.es/files/product_catalog/pdf/ci2-ilustrada-pat-16.pdf

All their stuff is available from your local parts supplier or Evilbay.

Merlin do a few things, self-sealing hose take-offs in various sizes that as the name implies screw into a hose and self-seal the joint, either for a pipe take-off or for sender units or switches. Also hose adapters - short sections of 25-45mm pipe with a threaded hole for the same thing. Trouble is, they're all about £20-25 each.

Is there nothing modern that has a similar set-up, where you could get the short rigid section with the thread from a breakers yard for peanuts? Oh for the days when you could just wander around looking for something suitable.

Out of curiosity, I've gone with the Klixon stat suggested by Darkspeed .
Listed as an 85 degree stat, a quick test (using a frying pan and an infrared themometer ) shows it turns on at about 85 and stays on till the temperature drops to about 60.
This has to a big improvement over the stat it replaced (originally a fish tank stat - that turned the fan on about 40 degrees!)

Quick pic 
It's currently clamped on the rad opposite the inlet hose so it should get an accurate reading.
Wiring is super-simple, a feed from the ignition to the stat - which triggers a relay when it gets up to tempature.
The relay has a direct (fused) supply from the battery for the fans.


It's only had a short trip into town so far but the temperature is looking good (warm, where before the fan was triggering far too soon)

Watch this space for updates 

Thanks again to everyone for the suggestions, it's all appreciated 

^ Good points well made

My other concern is that I have a slow water leak, if I run low on water the bottom hose should still give a true reading when the top hose might be confused by the air in the rad   Yes - the leak is on my list of things to fix!   

The beauty of it all is that for under a fiver I can get a 2nd stat and use the highter one to trigger a new-fangled warning light (and the 2nd electic fan)