On a 1966 Ford Mustang :
200 cubic inch inline six cylinder engine :
The spark plugs are gapped at ( .032 to .036 inch )
According to one of Fords websites : For a 1966 Ford Mustang , 4.7 liter / 289 cubic inch V8 engine : ( the spark plugs are gapped at .035 inch )
The 1966 Ford Mustang 200 cubic inch straight six spark plug gap is .032 to .036 inch
.024 to .026
.32 to .36
.032 to .036 inch
Check the ballist resister on fire wall !!!!
crash it.
The spark plug gap for a 1966 Mercury Marauder 410 6.7L V8 is .034 to .035 inches. The new spark plugs will not need adjusting, however, as they come preset.
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I was looking at one of the Ford websites and it shows for the 4.9 liter / 300 cubic inch inline six cylinder engine in 1966 : ( for light duty the spark plugs are gapped at .035 inch ) ( for medium duty the spark plugs are gapped at .030 inch )
You will still have spark, car will try to start or backfire. If no spark at all the plugs see if you have GOOD spark from coil. If coil is working then you will find the problem in between the coil and the plugs, probably a distributor component issue. The ballast resister is a possible cause also.
just ask them at the parts store, they will be able to tell you what plug you need.