Mazda Repair: 1990 miata automatic, air flow meter, vacuum diagrams

Question
QUESTION: problem #1: the fuel indicator needle is on 3/4 with no key in the ignition. is this grnd or short problem or can it be the ignition switch? sometimes i have to jiggle the key to get the heater & wipers to go on.i think that is what's draining the battery so bad after charging i can only get 2 starts out it it .is there a fuse i can temporarily disconnect for the gas gauge ?

prob #2:a mechanic measured low vacuum of around 2 but could not find any leak by spraying all over and even dropping the exhaust system.when i first start up i can rev the engine rpm's but when it drops to idle i can floor the gas and nothing- no power at all.
is there anything else that cause a low vacuum reading other than a leak ?

the air flow meter and iscv were replaced and the idle set by adjusting the throttle cable & idle dashpot screw.jumpering grnd & 10 didn't seem to make much of a difference in the adjustment process .

thank you so much

ANSWER: the gas gauge works on a resistance switch if it was a short to ground it would read either full or empty all the time depending on how the swith is wired. it could be a number of things it could be the resister itself or the gauge.

low vacuum can also be caused by alot of things a leak somewhere would cause low vacuum. as would a sensor fault or faulty switch look at the wiring and vacuum diagrams to see where the vacuum lines all go and also what sensors are controled by vacuum

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QUESTION: thank you- is it possible the no power / low vacuum reading could be caused by a bad ecu ? thinking back there was a small coolant leak .i could smell it but they couldn't find it. when i switched to outside air vs recirculated air the smell went away.they didn't check the inside heater for leas.thank you again ! also is there anyway to retrofit the 1990 with later year power mirrors ?

Answer
the ecu takes info from sensors and then takes that info and adjusts things in the engine as needed so yes a bad ecu can cause any fault code reading

i can assume you can retro fit power mirrors they do have universal after market ones so i'd assume yes they could be done as to how it would look i don't know