Voltage drop

[Doug&Deb]

I’m trying to determine if my ignition switch is bad. How much voltage drop is acceptable?

[Ivan_B]

How's voltage drop has anything to do with the switch? Are you monitoring the battery voltage and it goes down when you turn-on the ignition, or something like that? Please provide more info about the underlying problem.

To test the switch itself, you would normally check for continuity on the applicable contacts in applicable positions, with the multi-meter.

[Doug&Deb]

Yes I’m checking voltage with the key in the run position. Continuity testing is difficult due to the armored cable and the fact that I can’t get the switch to drop down far enough to get easy access to the terminals. 52 Coronet by the way.

[Sniper]

I don't like more than .1-.2v drop, especially on a 6v system.

 

 

[Doug&Deb]

That’s what I needed. Thanks 

[Sniper]

1 hour ago, Ivan_B said:

How's voltage drop has anything to do with the switch?

 

https://www.fluke.com/en-us/learn/blog/automotive/electrical-automotive-troubleshooting

[Dave72dt]

Basically voltage in versus voltage out.  A switch may have continuity but lack the capacity to transmit full voltage to the load it controls.  

[Sam Buchanan]

31 minutes ago, Dave72dt said:

Basically voltage in versus voltage out.  A switch may have continuity but lack the capacity to transmit full voltage to the load it controls.  

 

Often caused by severely degraded contacts. This is the same principle we see when trying to use 12v battery cables on a 6v system...the small cables will show continuity but not provide sufficient capacity to flow the current needed to operate the starter. Continuity and current capacity are two different functions. Voltage drop is a signature of reduced circuit capacity.

Edited March 18 by Sam Buchanan

[Plymouthy Adams]

Key point to keep in mind is the amp meter feeds the ignition switch but also all HOT circuits.  Many times the voltage loss is here and one needs only to clean and secure the wires affixed to the amp meter both from the battery and the down stream feeds.

[Doug&Deb]

You may be on to something PA. The dash light for the ammeter and fuel gauge went out about the same time as my problem started. At one point I reached up to try and find the bulb (unsuccessfully) . I may have jostled the wires and fixed the electrical connection. Dodge didn’t make it easy for someone with back problems to get to anything under there.