Join Date: Mar 2002
Location: Austin, TX, USA
These dang ol' cars develop all kinds of bad connections. There are two circuits to consider -- the ground and the hot. Bad grounds are common. Road crud and the elements will corrode ground connections. Also, if anyone has done work on the car, the chances are good that they left off a bonding strap somewhere. For some reason, ground straps fall into the bin of extra parts. The power feeds are also prone to corrosion and bad connections. Ignition switches develop dirty contacts that will loose voltage. The fuse clips had very poor plating and just about everyone I've seen has rust on the clips.
About the only way to tell what is going on is to start measuring voltage drops in your electrical system. In general, you should never see more than about 0.5 volts or so accross any switch, connector, or between any two assemblies that are grounded. I usually post that drops should be less than 1 volt. If you search this forum, you'll find lots of posts describing the technique. "Voltage drop" would be an excellent search term. Check them out and let us know if this doesn't get you going.
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI