I have a 1990 Mazda MPV with 193800 miles. When the van is wet it is very very hard to start. When it is wet the I tried to jump it and noticed a spark from the Plug 6 on the Distributer cap could it be needing a New cap or a new set of wires ?? and how do i change the cap.

 

Very good indication with the hard start when wet and seeing spark at the cap that the cap center button is burnt. Cap and rotor replacement might just get you all fixed up. Spark plugs too if it has been a while since they were replaced. Pic below of the cap and rotor separated from the distributor. Three bolts hold the cap on that can be removed with a #2 phillips screwdriver or a 8mm socket if they are too tight to remove with screwdriver. Bolts are spaced around the cap at approx 120' intervals. There is also a phillips bolt holding the rotor onto the distributor shaft that will have to be removed before trying to pry the rotor off.

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