Adding Circuits
Another difficulty facing car crafters that wish to upgrade their older supercars is that there are usually very few extra electrical circuits in these older cars that offer fusible circuit protection. Adding extra circuits on an as-needed basis is clumsy. A much more expedient method is to employ one of those add-on circuit boxes available from companies like Painless. These are pre-wired circuit boxes with built-in ATO-style fuses that can manage several circuits without overloading your existing fuse box. The biggest hassle would be finding a place to mount the box. Then all you have to do is wire up the circuits you want to add and you're ready to run. Painless offers these slick units in universal 3-, 7-, and 12-circuit blocks complete with fuses and a heavy-duty relay. Painless even offers a 12-circuit universal pre-wired fuse block that will replace your existing fuse box. These kits are very easy to install and will give a professional look to your wiring system.
Like most things in life, it's the little things that can trip you up and make you miserable. Eliminating those pesky electrical gremlins is about knowing how to do the job right the first time. Apply a little bit of electrical savvy to your next wiring job, and you won't have to pay the consequences of being stranded alongside the road with a melted harness.
The simplest voltage-drop...
The simplest voltage-drop test is to compare the voltage at the back of the alternator to the voltage at the battery posts. The ideal voltage difference should be no more than 0.4 to 0.5 volt. On this Camaro, we measured 14.4 volts at the back of the alternator and a mere 13.5 volts at the battery, which means this Camaro is losing 0.9 volts between the alternator and the battery--about twice the acceptable limit.
Drop It
One of the most valuable and easy tests you can run on any electrical circuit is a voltage-drop test. All you need is a digital voltmeter and a little bit of time. The voltage-drop test measures the amount of voltage that is lost in the circuit due to high-resistance connections, bad cables, weak switches, or a poorly functioning component.
The simplest test is to measure the amount of voltage drop that occurs between the alternator and the battery. Start the engine, and using your digital voltmeter, measure the voltage at the back of the alternator by placing the red lead on the alternator output terminal and the black lead on the alternator case for a ground. Then measure the voltage at the battery with the red lead on the positive and the black lead on the negative battery terminal. On our test Camaro, the alternator cranked out 14.4 volts, but the reading at the battery was only 13.5. This meant there was a 0.9-volt drop between the alternator and the battery. An acceptable voltage drop is more like 0.4 to 0.5 volt. We either have a wire with high resistance or a bad connection. We've seen as much as a 1.5-volt drop on an early Chevy musclecar traced to an undersized fusible link.
This illustration shows how...
This illustration shows how we tested both the positive and negative battery cables. With the engine cranking, we found a 0.6-volt drop for the ground cable and a massive 1.0-volt drop on the positive cable. By just changing to larger M.A.D. cables, we reduced the starting-circuit voltage drop in half to 0.8 volt total. There are other smaller changes we could have made to improve the circuit even more.
Remember that voltage-drop tests must be performed while the system is operating. Another popular voltage-drop test is with the starter circuit. GM cars are famous for "heat-soak" problems that occur because resistance increases with temperature. Again, the test can only be performed with the starter in operation. This produces a current flow and therefore a voltage in the circuit. To perform our test, we disabled the ignition, set the digital voltmeter on the millivolt (0.001 volt) scale, and tested each series of connections. For example, we tested the voltage drop for the positive battery cable between the solenoid and the positive battery terminal on a '68 Camaro. While the positive battery cable looked fine, we discovered a massive 1-volt drop in this cable alone! In order to record these high readings, we had to switch to the 2-volt scale on our multimeter. Combined with the smallish negative cable, the two cables alone produced a massive 1.6-volt drop in the starting circuit. The owner noted that the car had always had difficulty starting when it was hot. An acceptable level might have been around 0.20 to 0.40 volt for each cable.