Rusty_S85 Posted August 30, 2022 Share Posted August 30, 2022 I added the the new switch in parallel with the proportioning valve switch. That circuit in effect has four contacts in parallel on my truck: -A contact of the START position of the ignition switch (lamp test) -The E-brake switch (which the OP doesn't have) -The proportioning valve switch -The Master Cylinder switch (which I added) However, upon further review, the way that's done is a bit "unusual": https://forum.garysgaragemahal.com/file/n124202/Screenshot_2022-08-29_220010.png As the igintion switch contact runs through the shorted portion of the proportioning valve switch (the actual switching element shorts to ground); with the switch unplugged, the ignition lamp test will fail. Similar to the "newer" master cylinder switch, which (in it's intended application) has two of three contacts shorted together to do the same thing, only as an input to the ABS module, not as part of the ignition lamp test. Yep only way to have the test function with the key functional even with a switch failure or it being unplugged the circuit needs to be teed into a single circuit so even if the switch fails in the connector or becomes unplugged when they ignition switch hits start and provides a ground on the wire it will still be able to ground the wire for the bulb itself. Link to comment Share on other sites More sharing options...
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