Triumph Repair/1974 triumph spitfire 1500
where can I buy a vacuum diagram for the vacuum switch
to carburetor, that is located in the lower radiator hose?
BLM was very lax in supplying vacuum diagrams even to the BLM dealerships. I worked in several of the dealerships through the whole life span of the Triumphs and MGs in the US and we never had good vacuum diagrams of any of the BLM cars (MG, Triumph, Jaguar and Rover)
The only place I seen accurate vacuum diagrams was on the stickers they use to put under the hoods. The problem with that was that the stickers didn't survive very long even while the cars were still being sold. Why they didn't put those diagrams in their manuals I have never figured out. In the shop we often had to find another car in the shop to refer to when hoses were missing due to the short life of the vacuum stickers. And that was 40 years ago or so.
As I remember the multi vacuum ports in the temperature unit in the radiator hose was only used a very short time and it was elimited. You have to keep in mind that BLM didn't know what they were doing trying to meet the US emission standards. But then none of the other car manufactures were doing much better, including the domestic cars.
If you are trying to put the car back original, you might try Moss Motors as they have a toll free number and they have a tech department that may have vacuum diagrams. I know that they have reproduced other stickers for a wide range of British cars. But I have not seen any of the vacuum diagram stickers any where.