Vacum / pressure switch

[fastfredracing]

. I cannot seem to find this vacum switch for my old tow truck project . It is a 1977 Chevrolet c 60. Has vacum brakes, and a vacum switched 2 speed rear end.
I'm pretty sure it is supposed to alarm if the vacum goes under 8 hg .
Mine ist kaput, and just alarms randomly, and all the time while driving. It is really loud and annoying . It is also required , so I have to fix it .
I have full vacum, and no leaks, verified, by 2 onboard vacum gauges .
It looks exactly like any other 2 pole pressure gauge used on cars for as long as I can remember.
When I search for it, only pressure switches come up. I have randomly searched for several months now, and have not found one yet.
Will a pressure switch set for + hg, also close, and alarm for the same amount of - hg?
Im stumped.
Here is what it looks like. Threads into a little t fitting tied into my vacum booster vacum feed line.

Have any ideas where to find such a thing ??

[fastfredracing]

Picture did not load right

[pete3799]

This one is normally closed. Is yours open or closed.
https://www.summitracing.com/parts/sww-77343-04/overview/

[John Rogers]

Well that one does not appear to have any way to adjust it? Remember that anything above 0 PSI is pressure and we think of any thing below 14.7 PSI or 1 atmosphere is a vacuum. So if it where me I'd search for suppliers of heavy duty (C60 class) Chevy truck parts. Good luck.

[JackDidley]

Can you use something like this ??

https://www.amazon.com/Superior-Universal-Adjustable-Vacuum-Switch/dp/B00BZODN9A/ref=sr_1_5?s=automotive&ie=UTF8&qid=1535168307&sr=1-5&keywords=vacuum+switch

[908/930]

Search Honeywell 5000 series vacuume switch, there is a variety so you need to know normally open or normally closed contacts, and then what vac range and what terminals for the wires. And then figure out who stocks them.