Bruce Cotsell's low coolant alarms are reccomended. I've fitted 2 of them to TFs. Inexpensive and straightforward
Apologies for the shameless advertising, but since it's been mentioned above...

My coolant alarm kits are available from eBay for a reasonable price.  But members of The-T-Bar can benefit from a respectable discount by buying from me direct.  Just send me a private message here on The-T-Bar.  I am happy to send them abroad and do a LHD version.

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