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volt drop testing an ignition switch
Posted to Technical Tips Forum on 3/17/2009 23 Replies

This is one I fixed a month ago. The complaint was intermittent no start and several idiot lights intermittently lighting up.

After consulting my wiring diagrams,I decided to attack the circuit at the most accessible spot. I went for the underhood fusebox. [multimeter dual trace hookup]

I decided to setup a dual trace to show you exactly what a voltage drop is(not everyone knows).

This is a pic of what it looks like when the problem occurred. [voltage drop testing, dual trace] The voltage going into one circuit of the switch was 12.32v. Only 1.82v was going out under load. The difference in voltage between the two measurements is the "voltage drop", in this case, a 10.5v "voltage drop".

On this model, the instrument bezel is easily removed and gives access to the rear of the switch. [2000 Chevrolet Malibu, Ignition photo] While observing the dual trace setup, I gently pushed rear of the switch towards the front and the voltage drop disappeared. [no more voltage drop]

This is an internal view of the switch I autopsied. [2000 Chevrolet Malibu, Ignition photo] It uses a complex assortment of tumbler pins that apply pressure to superposed stainless "finger blade" type contacts. The whole thing appears quite cheap and flimsy, and I am not surprised they have a high failure rate.

Hopefully this will help some demystify what voltage drops are.

Karl from Quebec

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car Vehicle Data

2000 Chevrolet Malibu 3.1L

Engine3.1 L
Trans4-speed Automatic (Electronic)