When it comes to today's classic trucks, the amount of creature comforts being installed seems endless. Air conditioning, power windows, power seats, door poppers, and everything else one can think of all require more electrical power than most electrical systems and switches were designed to handle.
The big push to install relays to overcome the excessive loads on wiring and switches is a much-needed trend. Relays allow the power-consuming load to receive the current required without overloading the circuits and switches. These accessories will also perform at greater efficiency due to the increased power available.
Much of this is illustrated by Bill Marcom's '54 Chevrolet pickup. He was having starting problems and when the air conditioning was on, he smelled wires burning. Bill contacted John Roberts, a local wiring guy, to find the problem and make repairs.
Roberts examined the pickup and quickly realized that some relays and a little rewiring would have Bill on his way with much more confidence in his pickup's electrical system.
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 Problem number 1, the smell...  Problem number 1, the smell of burning wires when the A/C is turned on. Roberts started by tracing the burning wire smell when the A/C was turned on. The first thing he looked at was the ignition switch. He noticed several wires that appeared burnt. |
 With the tape removed, the...  With the tape removed, the severely burnt wires were exposed. This was a sure sign that the current load on the wires and switch was excessive. |
 The glovebox was removed to...  The glovebox was removed to expose the power relay for the A/C unit. The problem was easy to spot. The main power wire that was supposed to go directly to the battery, a battery source, or the starter solenoid was routed to the fuse block. |
 The main power wire was plugged...  The main power wire was plugged into the front of the fuse block, which meant all the power to operate the A/C unit had to pass through the ignition switch. |
 To repair the problem, Roberts...  To repair the problem, Roberts first mounted a 30-amp circuit breaker to the firewall and routed a 12-gauge wire from the maxi fuse to the circuit breaker. The circuit breaker will provide overload protection for the A/C power relay. The maxi fuse is connected directly to the battery cable at the starter solenoid to allow maximum current availability. |
 A length of 12-gauge wire...  A length of 12-gauge wire was then routed through the firewall to the power relay. |
 The power wire from the fuse...  The power wire from the fuse block to the relay was removed, and the new power wire was installed in its place. |
 The finished installation...  The finished installation will allow the A/C relay ample power for maximum efficiency and relieve the load on the ignition switch and wiring. |
 With the A/C working properly,...  With the A/C working properly, Roberts turned his attention to figuring out why the engine won't turn over when hot. It didn't take him too long to spot the problems. The wires were in bad shape from all the overloading, and the starter was hidden behind tight exhaust headers. Installing a Hot Shot relay to boost the available amperage required by the starter solenoid was determined to be the best fix. This relay reroutes current from the battery post directly to the solenoid activation terminal instead of through the ignition switch and harness. |
 First the relay base is mounted...  First the relay base is mounted on the firewall for easy access and distance away from excessive heat. The relay ground wire was installed with the mounting screw. |
 With the relay base mounted,...  With the relay base mounted, the main-power input wire was routed to the circuit breaker that was installed for the A/C relay. These circuits will not be used at the same time, so the circuit breaker will be able to handle each load. |
 The activation wire for the...  The activation wire for the relay was attached to the wire formerly going to the solenoid. The ignition/starter switch now activates the relay, which requires a slight amount of current, instead of the solenoid. |
 Here you can see the splice...  Here you can see the splice Roberts has made. |
 The relay output wire was...  The relay output wire was terminated and routed to the activation terminal of the solenoid. |
 The neutral safety switch...  The neutral safety switch had previously been bypassed with the jumper wire shown here. Roberts removed the jumper, and the two wires were reinstalled on the switch. |
 The finished installation...  The finished installation is clean and functional. Since adding the relay, the engine has never failed to start even when hot. Bill can now cruise comfortably with the A/C on and with the knowledge that the truck will start at the twist of the key. |