4. Ganged WiresLet's hope the positive battery post on your musclecar doesn't look like a bowl of spaghetti. Combine that with a typical unsealed battery and the connections quickly become corroded and nasty. The solution is to move all those wires off the positive battery post and onto a separate terminal block. MAD offers an inexpensive one (PN CN-1) that can accommodate several 8-gauge wires to power multiple accessories. This is also a great idea for an underhood power source for cars with the battery in the trunk. This block can be used to power up an MSD, electric fans, an A/C, and solenoids for nitrous along with at least a dozen other ideas. Hide this under the fenderwell and carefully route your wires and you'll be amazed how clean your engine compartment will become.
5. Hot-Start ProblemsMany slow cranking problems can be traced to high-resistance cables. Using high-quality MAD or Painless battery cables is the obvious solution. The MAD cable is impressive 1/0 gauge multi-strand copper conductor that is also double insulated. If the starter just grinds slowly, this is a voltage-drop problem. But if you've got the typical GM problem of the starter not engaging properly in a hot-soak condition, the cause is a major voltage drop across the solenoid-engagement circuit. The fix is as simple as using a Ford-style external solenoid in a kit from either MAD or Painless. The idea is simple: Mount the solenoid away from exhaust heat, which radically reduces the voltage drop across the solenoid circuit. Both kits also supply a shunt that connects the solenoid battery cable terminal to the small trigger post. Another advantage is that if you use one of these kits with a trunk-mounted battery, the only time the battery cable downstream from the solenoid is "live" is when the starter is engaged. This is a small point, but worthy of consideration from a safety standpoint.
6. Erratic Gauge PerformanceHave you ever had a set of electric gauges change readings when you turn on the headlights? This is caused by a poor ground circuit, a power circuit that cannot handle the additional load, or both. Most '60s cars provide power for the wiring harness through a tortuous path leading up to the fuse box under the dash. There are plenty of opportunities for power loss and voltage drops along the way.
The quick fix is to improve the ground path between the instrument cluster and the battery by adding those ground straps you threw away between the engine and the firewall. Then add one or two between the instrument panel and the firewall and see if the performance improves.
7. Relays RaceIf you've ever run a wire from that poor overloaded fuse box to power up an electric fuel pump, or if you've used a large wire from the battery to a switch and then to a heavy-duty electrical load like an electric fan, there's a better way to go than large clunky switches. Relays are a handy heavy-duty switching device that can be activated by a very low voltage switch. In fact, computers use relays to control high-current-draw items like electric fans and electric fuel pumps.
Here's how relays work. Let's say you're going to bolt on a 20-amp electric fan. You could run a large 8-gauge wire from the battery all the way up to a switch under the dash and back to the fan. Instead, mount a relay between the fan and the battery. This creates a shorter power path from the battery to the fan through the relay. Then you can use any light-duty switch to control the fan. Relays also work well for reducing the voltage drop on '60s GM car headlight circuit. Mount a pair of relays near the headlights and eliminate the long power path through the headlight switch. This shorter path through the relays puts much more voltage to the headlights, making them much brighter.