Question: My 1979 F-159 pickup (300 six) ignition seems abnormally sensitive to moisture. Recently on a damp morning it wouldn’t start at all. I’ve checked for the usual sources of this problem and not come up with anything. Is there anything special to look for with this ignition?

Answer: Wait till damp evening and open hood while running engine, look for small sparks jumping around between wires/coil and metal. prob will show u where your problem is. Top or coils become porous and cracked in very old coils too,moisture will short spark to ground an no start.. Also plugs get lot of dirt built up and can short down insulator ceramic. Also plugs with a real wide gap can make it difficult for spark to jump and it will jump thru old wires/dist cap etc. next time it won’t start, spray WD40 on top of coil,dist cap,wires. Hit these items 1 at time then try starting to see if that was causing problem.(the WD40 displaces moisture). I have had the same problem with my 77 Bronco. Recently, especially on wet days, I wasn’t getting spark to the plugs, even though I got spark from the coil. It turned out that somewhere between my ignition switch and the first ballast resistor of my ignition, I was losing voltage, probably due to a corroded or dirty connection somewhere, so my coil was generating a very weak spark. Rather than try to find it, I simply rewired it (this isn’t the first time I’ve had to rewire something on that old rust bucket). Dirty or corroded connections or otherwise bad wiring can often be quite sensitive to moisture.
I received a lot of help from this group on ignition wiring. The first thing to do is to check some voltages at various places on your ignition. With your distributor at a position where it should be firing (a current load is placed on the circuit), you should have 12V to the distributor and about 7-9V to your coil (the voltage is reduced with ballast resistor(s)). If there is no voltage drop across the resistor(s), turn the engine a little at a time until you load the circuit and read a drop. In my case, the voltage to the dist. was only 8V and the coil was only getting 5V, due to the bad connection. This is too low. You can trace the problem back towards the switch or the battery if you want to by determining where you lose that voltage when the ignition is (or should be) firing.
Good luck. Electrical problems are never any fun.

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