MTFCA Forum

As you all know I am a electrical dummy so please don’t laugh at this question as someone recently posted about wires too close together causing electrical interference.
The number 4 spark plug wire in the picture from the coil box post to spark plug runs right next to the lower coil box post which I believe is from the ignition switch to the coil box. As long as they do not touch and are insulated is this a problem?

Probably OK, but if it was that way on my car I would fix it. If you are using pre-cut spark plug wires from the vendors, put the shortest wire on plug #3. This will give the wire for #4 just enough extra length to give you some extra clearance.

I bend the plug terminal up and move the plug wire away from the coil box terminal. Retighten the plug wire in the newer position and it’s good to go. It’s not touching anything in that position.
Your probably OK as yours is but I try not to let any plug wires touch another terminal even though they are insulated. Ford probably didn’t do it when the cars were new.

I think Mark is on the right track, #4 wire is too short. I checked my original wires on my unrestored '24, and #3 and #4 wires are the same length. If your new wires have four different lengths, swap #3 with #4, #4 should not be the shortest wire.

It's best to keep the high tension plug cables 1" or more away from each other or anything else. Also check that linkages do not move into contact with the plug cables when the controls are operated. It's common for plug wires to leak current to anything near them. Inductive coupling can also occur, but is less likely than insulation leakage. All high tension insulators, including the plug insulators and coil box and coil casing parts exposed to the high tension current, need to be kept clean and dry. Any wood exposed to high tension current that is dirty or in such a condition that it can absorb moisture is likely to leak current. Any slight leakage will usually cause carbon tracking, which leads to more leakage.

That's the reason they have insulation on the wires! When I did mine, I referred to the Ford Service book, and routed my wires exactly the same as the pictures in the service book.

On the 1928-'31 cars, Ford did away with all insulation on the high tension side and used bare metal conductors to carry the high tension current from the distibutor to the spark plugs.

Yes, I have seen barbed wire used as a joke!

Might the loom wire to the coilbox be routed around the end of the terminals rather than down through them. It works on or RHD cars.

Allan from down under.

I'm a little surprised that some "Old Timer" hasn't suggested this test already. So, this "Old Timer" is going to make the suggestion.

Take your car to a DARK area. Start it, open the hood, and look for sparks from the high tension (spark plug) wires. You'll be able to see sparks between the plug wires and anything else. Then, you'll know exactly where the problems are.

Good Luck

Allen, This is how the USA left hand steering firewall configuration is in the Ford Service Manual copyright 1926.

Thanks Geoff,
There does seem to be plenty of length in that wire to route it down past the end of the box and along under the spark plug terminals to keep it out of the way.

Allan from down under.

Run your motor in the dark, sparks jumping between wires will easily become evident. My Dodge was running poorly until I opened the hood one night out in the driveway and saw the lightshow. Had sparks jumping from the spark wires to the headers on 4 cylinders. Don.