turn key off turns instrument cluster off.. not the oil switch.. its still a ground.. other side of light is the silly black wire he does not wanna tap into...
the relays that use a 87a tend to have 30 powered by the key.. not hot all the time...
to swap just a 87 and 87a relay.. it will stay powered when the op switch makes ground.. you cannot tease a relay to work properly in floating mode.. has to be ground or power...
so to use yes/no oil pressure with a stock switch cannot be done via relay... unless you kill power to the actual relay..
he is not using the stock oil light system.. he is trying to add a 3rd oil switch for this to be some sort of on/off switch..
now if a gm switch works ass backwards.. makes ground with pressure.. ok that will work... but my knowldge.. usually ground when no pressure.. but gm is not my depth of knowledge..
my guess how he thinks to wire this idea up... ill note it with flaws...
30, 86 batt
87 his pump and all..
85 oil switch.. some how he thinks it will ground... and the cause for this debate... only ground with no pressure
so ignore that with a 87a style relay.. that your saying will work... again ill note the flaws...
30, 86 batt... needs to be key, gm does this lots w/key powered source...
87a pumps and stuff
85 op switch.. not running = ground= turn on 87 and 87a off... when running turns relay off and 87a on turning on pumps/fans...
see why 87a stays on? yes pump and all off.. but relay coil inside relay has power... this will kill batt after 2 days... ive parked cars with light/radio kill relay installed with key in ignition... how i know 2 day time.. takes some idiots who borrow cars a few jumps to not do that...
he cannot use the original 0.7v idiot light to power the relay either... burn up the cluster that way... and would screw up his oil light system function too
yes all cars use this relay in some form.... 30, 85,86,87/87a you will find in all fuse boxes... micro.. big.. fused.. knowing when 87 or 87a has power is key to jumping most fuel pump relays... dodge, ford, gm all do... vw is the screwy screwed up one... but its still got 30 and 87... cross and eliminated it is.. those 4 relay numbers really do cross bread in cars... and can help "manipulate" items your testing..
im thinking dodge uses 1-5 vs the 30, 85, 86, 87/87a numbers.. but to look at the schematic on the side.. its still same relay..