Join Date: Mar 2002
Location: Austin, TX, USA
Measure the resistance of each one of your wires using a digital ohm meter. The resistance will be in units of ohms per foot, so the longest wire will have the highest resistance. You can get all sorts of wire resistances from a few ohms to 4000 Ohms. But if you have an open wire, it will probably read much higher if at all.
You might want to poke at the wires with a stick before starting though (engine running). The problem may be sensitive to position. If so, you'll grab it, measure it and think its a good wire until it's back in position.
There are some pretty cruddy wires on the shelf these days. The cut to length wires can be especially bad. Many have a conductive plastic strip down the middle. Looks like a strip of trash bag. Just a few hours and the plastic strip will melt away from the terminal and create heat, which melts the plastic further, until it doesn't work anymore.
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI