How to Install an Amp Gauge on a One Wire Alt

by Kurt Schanaman

The ability to monitor the amperage of an automobile alternator is essential for those who have installed high-power usage equipment, whether the equipment consists of appliances in an RV or high-wattage stereo equipment such as amplifiers. The amperage gauge should permit you to keep tabs on how your alternator is keeping up with the power draw so damage doesn't occur to the alternator or the equipment. Some alternators are connected using only one wire for the positive terminal, and the negative connection is through the mounting bolt that connects the alternator to the automobile frame. Making use of this configuration requires the harnessing of the frame-mounting bolt.

Step 1

Mount your amp gauge in your vehicle to facilitate brief glances without ignoring the road ahead of you. Use the screws included with the gauge.

Step 2

Locate a pass-through hole behind your dash on your vehicle's firewall and run your gauge wires through the selected hole, feeding at least a 1-foot length into the engine compartment.

Step 3

Open your vehicle's engine compartment hood and locate the wire ends you pushed through into the engine compartment. Pull the remaining wire length through gently and route them so they don't get caught in the engine fan or come into contact with any hot engine surfaces. Stretch the red positive wire to the the positive terminal of your vehicle's battery, and stretch the black negative wire to the mounting bolt of your alternator.

Step 4

Crimp a wire terminal onto the end of the red wire coming from your amp gauge. The terminal should be suited to the diameter size of your vehicle's battery terminal so you can slide it down over the battery terminal. Remove the positive (+) battery terminal and slide the newly crimped terminal down over the battery post and press the battery terminal downward tightly onto the newly installed wire terminal. Tighten your battery terminal for good contact.

Step 5

Crimp a round wire terminal onto the end of the black negative wire (-) coming from your amp gauge. Remove the alternator mounting bolt with an appropriately-sized socket wrench and separate the alternator from the vehicle's body about 1/4 inch. Position your newly crimped wire terminal between the vehicle body and the alternator mount. Push the mounting bolt through the alternator mount, the wire terminal and on into the vehicle body. Tighten the bolt fully with a socket wrench of appropriate size.

Start the vehicle and make note of the alternator's amperage reading on the gauge.


  • On automobiles, regardless if an alternator is of the one-wire variety, the electrical pathway always flows from negative to positive. The automobile body and frame is the negative "ground" and the other end of the circuit is at the positive battery terminal (+). The negative part of the circuit always flows through the body of the vehicle, terminating at the negative (-) terminal of the battery. When connecting any device to the body of a car for the ground (generally a black wire), you must make sure the metal surface is scraped clear of debris, rust, oil or other contaminants so that your connectors are all touching bare metal. Use a wire brush or a scraper to clean the surface where you mount your negative terminal to the body for best results.

Items you will need

  • Measuring calipers
  • Socket wrench set
  • Screwdriver set
  • Round wire terminal sized to the diameter of the alternator frame mount bolt
  • Crimp-on wire terminal sized for your battery's positive terminal
  • Wire terminal crimping tool

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