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Bad ignition switch?

Started by J-440, December 17, 2017, 06:36:34 PM

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J-440

 Been chasing an electrical gremlin which is always fun.  Here's the skinny: Car idling at 800rpm and am getting 14.5 volts from the alternator, 14.2 at the battery in the trunk, but my FAST ECM on my laptop reads 10.9 volts. These are readings with everything turned on.  Been talking with FAST and I think we've narrowed it down to a bad ignition switch terminal.  This is the stock (repro) ignition switch but with modern upgrades like EFI, lights, electric fan, etc.  Since the FAST EFI main power wire is going to the switch, then goes to the battery, why the heck am I getting 2 different readings? 
  The alternator is a new 140amp and Powermaster says that with my setup, I'm borderline.  Now to make things more confusing FAST recommends 1 gauge wire from the alternator (+ and - terminals) be ran all the way back to the battery.  I did that and only saw a gain of .2 volts on my laptop. I also read the FAST power wire going to my ECM and it was a solid 11.8 volts.  Any ideas?
 
68 R/T, 440/727 6-speed, SC G-machine...black suede

BLK 68 R/T

Shouldn't the main power wires go directly to the battery?

J-440

 Yes and they do.  The wire from the ecm to the ignition switch has got me wondering though. Could the terminal be bad?
68 R/T, 440/727 6-speed, SC G-machine...black suede

W4ATL

Check the voltage at the point where you are powering the ECM. Is the voltage low there? Then work back to the bulkhead connector. There is a drop somewhere, either at the bulkhead, the switch or the wire from where you pick up the voltage.

chapel40

I had a wire getting hot at ignition switch connector on bottom of steering colmn and engine bulkhead connector. had to cut and splice them together.
Don Chapel

John_Kunkel

Quote from: J-440 on December 17, 2017, 06:36:34 PM
14.2 at the battery in the trunk, but my FAST ECM on my laptop reads 10.9 volts. These are readings with everything turned on. 

This is a good example for the argument to use relays to power critical devices, use the ign. switch to power a relay that switches power directly from the battery to the device.
Pardon me but my karma just ran over your dogma.

J-440

 All great ideas. Gonna try em out this week. Thanks.
68 R/T, 440/727 6-speed, SC G-machine...black suede

J-440

 Just did a parasitic draw on my battery and I do have one.  It's 140 milliamps.  I know if you have higher than 50 milliamps you need to do some fuse pulling.  Don't think this would be the issue, though these FAST systems are sensitive.  I still think it's somewhere in the switch or maybe the bulkhead connector.   
68 R/T, 440/727 6-speed, SC G-machine...black suede