Re: Locating a short circuit

Posted by Gar On 2021/4/7 15:37:16

What year is your Packard?

You could have a weak ground (normally the positive wire on a 6 volt system most often negative on a 12 volt system).

As mentioned in the earlier threads; 1-a dirty relay or a through hole fitting could also cause your problem.
1-Relay will get warm/hot with usage and can cause the contacts to expand slightly. If the contacts are dirty or pitted, this will generate more heat and cause great expansion resulting in possibly dropping the circuit temporarily.
2-wire insulation could be frayed or missing a rubber grommet where it passes thru a piece of metal (firewall/fender). You could also have a corroded connection.

Assuming you are not continuously blowing fuses... (with the motor turned off, using an accurate DC volt meter: check battery terminals (+ to -) and record voltage; check battery to relay/ammeter (input side) and record voltage; check output side, record voltage; check input side of switch, record voltage; output side (dimming off), record voltage...and continue all the way to the light socket. Time consuming and tedious. If any voltage varies at any device, you can by pass that device and continue testing.


I however, am a believer in the 50% rule. Split the wiring circuit in half and trouble shoot at the source (ie:battery) to the midpoint of the circuit. So battery to light switch then... light switch to something between and light socket (junction box/wiring connectors).

Voltage should drop very little from end to end. Also grounding issues can cause problems as well.

Best of luck