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Kill switch issue

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#1
Dave Metz

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At Mid Ohio today and went to get my annual tech due to a late start this year. On being teched, kill switch wouldn't shut off car. If switched off it will not start, but if already running, it just kills the dash and the motor does not stop. I have a four post switch with the battery positive split and going to the two large lugs. The alternator exciter wire (grey with red tracer) is split an goes to the small lugs. I have tried changing out the switch, changing the wires around the switch in every combination and pulled the roof and package tray to confirm that it was the correct wire that was split and goes to the small lugs. Nothing has worked. Any suggestions?
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#2
Steve Scheifler

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Switching the exciter won't work. You need it hot only long enough to "excite" the alternator and get it charging, then all it does is have power from both ends to keep the warning light off.

You should be switching the main B/output instead, and through the protection resistor.
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#3
Dave Metz

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Where would that be located?
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#4
KW78

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Did it used to work correctly?

 

The 99 alternator has the field wire dithered from the ecu and if you interrupt that wire, the alternator does collapse and not charge.  With the alternator not charging, the car dies with the master switch.

 

However, if you have an earlier alternator, they are self exciting as well and once going, keep the car running.  I wonder if you have the correct alternator, because the earlier ones fit the hole and hookups.  This is a common problem with remans because the cores are visually the same or very similar.

 

I stopped prepping cars this way however, because we kept having intermittent ECM failures of the charging circuit.   We started running the main EFI relay ground thru the 2 small poles of the master.  No current, and very effective.

 

My 02

Kyle


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#5
Steve Scheifler

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Where would that be located?


It's the large single (probably white) wire to the alternator, held by a 10mm nut. But I think I like Kyle's approach better unless somebody can think of a downside.
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#6
SaulSpeedwell

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dbl post


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#7
SaulSpeedwell

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It's the large single (probably white) wire to the alternator, held by a 10mm nut. But I think I like Kyle's approach better unless somebody can think of a downside.

 

Many of the kill switches are only rated for 5-10A on the small terminals, not the 40-100A of the various "main" relays used from 1990 to 2014.  We believe a car at Mid Ohio last weekend failed due to heat from excess current (and/or arcing) inside the small side of the kill switch.  It was one of the cute/frail European-type switches with the key, and the small terminals were breaking the 10-ish gauge Main Relay output/throughput wire (White with black stripe).  I'm assuming that is NOT what Kyle is doing since he says his method has "no current"? 

 

Most direct-contacting switches like these are designed to be "self-cleaning" - meaning they need to be used occasionally or frequently to keep the contact points clean.  Like a Salt Belt car's e-brake, you should probably use it frequently or never.  This is anecdotal data at best, but it seems to me that guys that use their kill switch frequently have fewer kill switch and charging circuit issues (esp. on NBs).

 

There are many ways to make a kill switch system that works - I prefer breaking the battery ground on the big side, so that in any situation where that wire gets pinched (crash) or falls off or a wrench hits the terminals, it is harmlessly shorting "ground-to-ground" with no sparks, heat, or boiling battery drama.  On the small side, I like breaking a nice little <1A switching signal that is before the "main relay", which is usually the one coming from the IGN switch in some fashion.

 

My favorite method is what V2/Provitz does - uses a DC-DC contactor (e.g. Stancor 586-903, 600A surge, 200A continuous rated) to break the battery wire back by the battery with no additional wire, and then trigger that relay while breaking the little wire with any puny 4-terminal kill switch located wherever YOU want it without having to worry about running battery cable all over the car.


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