After attending the recent NSRA Street Rod Nationals, I came home with several concerns about the electrical systems in Rods that are being built today but more so of Rods that have been built for several years.
Electrical systems and add on accessories are changing so rapidly and demanding so much more, it is almost impossible to keep up. Alternators are twice the size of ten years ago to try to keep up with current demand of creature comforts.
I spoke with a rodder that purchased a wiring harness 9 years ago and is just now ready to install it. 9 years ago we had the wonderful 65 amp Delcotron alternator and maybe a small electric fan. The wiring in the harnessing then reflected the typical loads of the time. What happens now when we add a 140 amp alternator to power an amp guzzling electric fan, air conditioning, halogen lights power this and power that. Then we had an amp gauge that might read 60 amps, today it would go up in smoke in the first 10 minutes if it lasted that long. Another rodder was having problems with his system. Every time his electric fan came on the voltmeter went to 10 volts and the engine died. His electronic fuel injection computer required 10.5 volts to operate and was starved for current due to the fan.
Voltmeters are today’s way of seeing what the vehicles electrical demands are doing and how these demands are being met. They can tell us many things from how the charging system is functioning to if the loads on the wiring are too great. Knowing how to read the voltmeter is the key.
Relays are today’s answer to power transfer of current to those hungry creature comforts. Relays are a lot like voltmeters. Proper use will provide relief of worry about what’s happening in your electrical system.
Photo # 1 shows a voltmeter reading about 14 volts. This is normal for most charging systems ( 13.6 to 14.8 ) with no excessive load on the electrical system. A slight change of maybe 1 volt will probably occur if the lights are turned on or the windows are rolled up.
Photo # 2 shows a much larger voltage drop. This can be caused by the electrical system not capable carrying enough current for a specific load, such as an electric fan.
If such a drop occurs on your voltmeter a couple of things can be done to locate the draw. First, with the engine running, check the output at the back of the alternator and see if it is the same as what the voltmeter is reading (photo 3). If it is higher, the problem is excessive load on the fuse center, wiring or ignition switch ( most ignition switches have a maximum capacity of 60 amps ).