Airbag: mála aeir, though I would not find fault with aermhála either.
Blinker, direction indicator: táscaire. Masculine: an táscaire, an táscaire, na táscairí, na dtáscairí.
Brake: coscán. Masculine: an coscán, an choscáin, na coscáin, na gcoscán. To brake: na coscáin a chur air. Brake light: solas coscáin, obviously. Solas is a first-declension masculine - an solas, genitive an tsolais - but has the form soilse in plural, both nominative and genitive.
Car, automobile: carr, gluaisteán, mótar. All three are masculine, but referred to with a feminine pronoun. Carr has the genitive cairr, plural carranna: an carr, an chairr, na carranna, na gcarranna. Gluaisteán is a regular first-declension masculine: an gluaisteán, an ghluaisteáin, na gluaisteáin, na ngluaisteán. Mótar is a first-declension masculine noun too - an mótar, an mhótair, na mótair, na mótar - but I have the impression that in Kerry, where it is a well-established word in the dialect, it frequently takes the English plural endin, thus na mótars both in plural nominative and genitive.
Carburettor: carbradóir. Obviously a masculine: an carbradóir, an charbradóra, na carbradóirí, na gcarbradóirí.
Check valve: comhla choiscthe. Comhla 'valve' is feminine: an chomhla, na comhla, na gcomhlaí, na gcomhlaí.
Clutch: crág. Feminine: an chrág, na cráige, na crága, na gcrág. Clutch pedal: troitheán cráige. A pedal is troitheán, masculine: an troitheán, an troitheáin, na troitheáin, na dtroitheán.
Crankshaft: cromfhearsaid. Feminine: an chromfhearsaid, na cromfhearsaide, na cromfhearsaidí, na gcromfhearsaidí.
Cylinder: sorcóir. Masculine: an sorcóir, an tsorcóra, na sorcóirí, na sorcóirí.
Differential gear: giar difreálach.
Drivetrain: gléasra cumhachta. Gléasra is masculine: an gléasra, an ghléasra, na gléasraí, na ngléasraí.
Engine: inneall. Four-stroke engine: inneall ceithre bhuille. Two-stroke engine: inneall dhá bhuille. Rotary engine, Wankel engine: inneall rothlach. The word inneall is obviously masculine: an t-inneall, an innill, na hinnill, na n-inneall.
Fog lamp: solas ceo.
Gas pedal: luasaire. Masculine: an luasaire, an luasaire, na luasairí, na luasairí.
Gear: giar. To change gear is obviously giar a athrú, to gear up is giar a ardú, to gear down is giar a ísliú. Thus: d'athraigh mé giar 'I changed gear', ardaigh giar! 'gear up!', ísleoidh sé giar 'he will gear down', 'the clutch came into gear' chuaigh an chrág i ngiar. The word giar is a first-declension masculine with the plural giaranna, i.e. an giar, an ghiair, na giaranna, na ngiaranna.
Gearbox: giarbhosca. Masculine: an giarbhosca, an ghiarbhosca, na giarbhoscaí, na ngiarbhoscaí.
Hatchback is cúlhaiste. If referring to a car type, it is carr cúlhaiste. Cúlhaiste is masculine: an cúlhaiste, an chúlhaiste, na cúlhaistí, na cúlhaistí.
Headlamp: solas tosaigh, ceannsolas. Declension for solas is an solas, an tsolais, na soilse, na soilse; similarly, an ceannsolas, an cheannsolais, na ceannsoilse, na gceannsoilse.
Immobilizer: bac dúisithe. There's a good Irish term! Note that dúisigh!/dúiseacht does not only mean 'to wake, to awake' but also 'to stir, to start [an engine]'. Bac as a noun - 'hindrance, barrier' - is a regular first-declension masculine: an bac, an bhaic, na baic, na mbac.
Minibus: mionbhus. Masculine: an mionbhus, an mhionbhus, na mionbhusanna, na mionbhusanna.
Minivan: mionveain. Feminine: an mhionveain, na mionveain, na mionveaineanna, na mionveaineanna.
Number plate (license tag): uimhirphláta. Masculine: an t-uimhirphláta, an uimhirphláta, na huimhirphlátaí, na n-uimhirphlátaí.
Overdrive: forthiomáint - a feminine noun, thus: an fhorthiomáint, na forthiomána, na forthiomáintí, na bhforthiomáintí.
Parking light: solas páirceála.
Petrol (gasoline) is peitreal, masculine: an peitreal, an pheitril.
Piston: loine. Piston ring: fáinne loine, obviously. Piston rod: slat loine.
Propeller shaft: seafta liáin. Seafta is masculine: an seafta, an tseafta, na seaftaí, na seaftaí.
Sedan: carr salúin.
Sidelight: taobhsholas.
Spark plug: spréachphlocóid. Feminine: sg. nom. an spréachphlocóid, sg. gen. na spréachphlocóide, pl. nom. na spréachphlocóidí, pl. gen. na spréachphlocóidí.
Station wagon: carr fada.
Steering wheel: roth stiúrtha.
Tailpipe: sceithphíopa, although I remember having seen píobán sceite too. However, I guess sceithphíopa is better.
Throttle: scóig.
Torque converter: tiontaire toirc.
Traffic sign: comhartha bóthair. The word comhartha is masculine: an comhartha, an chomhartha, na comharthaí, na gcomharthaí.
Transmission: tras-seoladh. (You do see it written traseoladh too, but I guess tras-seoladh is better.) It is obviously masculine: an tras-seoladh, an tras-seolta.
Van: veain.
