mrmustang Posted January 25 Share Posted January 25 Have the following mystery switch (no spare wire to be found), believe maybe it is a low pressure brake light switch ????? Can someone identify for me so I can dig into the wiring diagram to see what wire should be hooked up to it. Or the part number I need to replace it.... Thanks in advance, Bill Link to comment Share on other sites More sharing options...
MV8 Posted January 25 Share Posted January 25 Those look like oil pressure switches on a remote manifold. Link to comment Share on other sites More sharing options...
mrmustang Posted January 25 Author Share Posted January 25 Just now, MV8 said: Those look like oil pressure switches on a remote manifold. Any idea what size thread they are on, since there is no wire for the circled switch, I'd like to remove it from under the hood (bonnet). Bill Link to comment Share on other sites More sharing options...
MV8 Posted January 25 Share Posted January 25 (edited) You can purchase a thread gauge (one is included with most tap and die sets but it would be for metric or sae, usually not both) or take the removed switch to the hardware store, then find a bolt where the threads mesh. They may have a thread gauge checker hanging on the wall. Armed with the thread pitch, rough measurement of the od will get you the plug size. On second thought, these are usually pipe thread, so I expect it is probably 1/8" and BSPT versus NPT. They look interchangeable and will screw into a hole but they won't seal even with tape. Edited January 25 by MV8 Link to comment Share on other sites More sharing options...
mrmustang Posted January 25 Author Share Posted January 25 2 hours ago, MV8 said: You can purchase a thread gauge (one is included with most tap and die sets but it would be for metric or sae, usually not both) or take the removed switch to the hardware store, then find a bolt where the threads mesh. They may have a thread gauge checker hanging on the wall. Armed with the thread pitch, rough measurement of the od will get you the plug size. On second thought, these are usually pipe thread, so I expect it is probably 1/8" and BSPT versus NPT. They look interchangeable and will screw into a hole but they won't seal even with tape. I'll try to get out today, believe it was an oil pressure sender as I got a drop or two of oil out as I removed it. Clearly it has been replaced by the silver pressure sender above it, so now the hunt for a proper plug will commence. Link to comment Share on other sites More sharing options...
JohnCh Posted January 25 Share Posted January 25 Is it possible it's a low oil pressure switch to trigger a dash light? Link to comment Share on other sites More sharing options...
mrmustang Posted January 25 Author Share Posted January 25 1 hour ago, JohnCh said: Is it possible it's a low oil pressure switch to trigger a dash light? Absolutely possible, however, without any spare wires other then the engine harness itself, I'm stumped. Part number is HPS (high pressure switch) then 2155 or 2165 . Saw that it was screwed into an adapter, which was then screwed into the billet distribution block, just pulled and cleaned that and will be headed off to Ace first, if no luck there, then Grainger on Monday. Thinking just a simple plug will do at this point will do. Not certain I'll pull the dash and start chasing wires, maybe if I lose sleep over it I'll dive in, but not likely. Bill Link to comment Share on other sites More sharing options...
JohnCh Posted January 25 Share Posted January 25 I only mention it, because if that's what it's for, it's a nice thing to have. Link to comment Share on other sites More sharing options...
MV8 Posted January 25 Share Posted January 25 (edited) I expect it opens above 5 or so psi and grounds a light on the dash that is powered (key in run ) off the normal instrumentation. The larger one is a sender/sensor for the oil pressure gauge and has a resistance that varies with pressure. I expect it is either 1/4-18 or 19 or 1/8-27 or 28. For a car that does not have ecm control of the fuel system, it could also be replaced with a switch that closes with a few psi to control a fuel pump relay, with a small momentary (like a tiny horn button) to prime the system if needed when cranking cold. Edited January 25 by MV8 Link to comment Share on other sites More sharing options...
mrmustang Posted January 25 Author Share Posted January 25 1 hour ago, MV8 said: I expect it opens above 5 or so psi and grounds a light on the dash that is powered (key in run ) off the normal instrumentation. The larger one is a sender/sensor for the oil pressure gauge and has a resistance that varies with pressure. I expect it is either 1/4-18 or 19 or 1/8-27 or 28. For a car that does not have ecm control of the fuel system, it could also be replaced with a switch that closes with a few psi to control a fuel pump relay, with a small momentary (like a tiny horn button) to prime the system if needed when cranking cold. 1/4" 18 pipe thread, not British thread on the adapter that screws directly into the block, the adapter was a 10mm 1 thread style. I've got my oil/gas pipe dope (what OEM's use for sensors and such) drying on the threads of the new plug for an hour, and will then install it in the block, let it sit overnight, and fire it up to check for potential leaks. Bill 1 Link to comment Share on other sites More sharing options...
jbcollier Posted January 27 Share Posted January 27 I like to run an oil pressure gauge and an oil warning light. You may not notice a suddenly lowering oil pressure gauge until it's too late. This? This you will notice... (from my Lotus Europa) Link to comment Share on other sites More sharing options...
mrmustang Posted January 27 Author Share Posted January 27 10 hours ago, jbcollier said: I like to run an oil pressure gauge and an oil warning light. You may not notice a suddenly lowering oil pressure gauge until it's too late. This? This you will notice... (from my Lotus Europa) I did order a low pressure switch over the weekend that I can always install in that spot, just not likely to do so at this time. Thanks Bill Link to comment Share on other sites More sharing options...
Joe Petty Posted January 29 Share Posted January 29 Looks like you have the best of both worlds for checking oil pressure: gauge or light! That block may be a universal solution, cheaper to stock one item and maintain one part number... It was not uncommon to use very low oil pressure as a method to cutoff an electric fuel pump in racecars. In the event of an incident, the pump goes off with the engine before safety arrives. Hence, a gauge to monitor oil pressure and a on/off oil pressure switch (and circuitry) to cutoff the pump. Downside is that a momentary switch (push button or spring toggle) may be needed to prime the carbs on startup. Good Luck - Joe 1 Link to comment Share on other sites More sharing options...
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