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Discussion Starter #1
'95 F-250 5-speed 4x4, two of 'em actually, 153,000 and 63,000 mi.

Security of the key cylinders is, well, sub-optimal; with some fiddling, either key will start the other truck, and there's a point where you can remove the key and still turn the cylinder in one truck. Yeah, we'll try powdered mica in the cylinders, and NEW (code-cut) keys, but I think it's time for kill switches in both trucks. Secure undisclosed location, yada yada yada....

Obviously no ignition kill. I couldn't find an easy way to kill the PCM or fuel from the in-cab wiring. So I'm going for a starter kill. A switch in series with the clutch safety switch wiring. I tested the circuit and it (low side of the starter relay) draws 3 amperes, so a 15A-rated SPST dash switch should get 'er done. Looking at the diagram, I don't think I'm in for any surprises. It's a totally separate circuit from the clutch switch contacts for the cruise.

Here's a mock-up diagram from the EVTM, with my idea drawn in:


Of course, I'll solder and heat-shrink the splices and terminals, and loom the wires. Only wire I have to cut is the red/blue one just downstream of the clutch switch.

Ideas? Issues? Caveats?
 

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Don't EFN worry about it
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Cigarette lighter system ground .
 

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Discussion Starter #3
How is that connected to the starter? Or the fuel system? I know it's tied to the OBD-II port, but shoot, we ran with that fuse blown for a week. Yes, I did a search, and found nothing about the lighter ground being tied to engine starting / running. What am I missing?
 

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Don't EFN worry about it
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Thought ytou said you wanted a security system .I will reread post.
 

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I modified my clutch interlock switch by adding an on-off-on SPDT switch to the wiring. Center position is off--opens up the clutch interlock circuit, so no starter motor. Other position is normal, clutch interlock is in circuit. Other "on" bypasses the clutch interlock switch so you can fire starter motor without pressing clutch.
 

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Here's a sketch.
 

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Discussion Starter #7
^^^^ Cool; same idea, deluxe edition. Yeah, I kinda like an override to the clutch switch; I've got it jumpered on my little Saturn. I'm a little leery of doing this on such a bigeffin' vehicle, though. I think for those rare occasions I need to bypass it (like to reach in to turn the key while diagnosing/repairing something), I'll just temporarily jumper it.

But the switch hasn't given you any trouble, functionally?

Alijay, I think I saw what you were alluding to on another forum. Someone re-purposed their lighter to close the "coil" circuit of a relay, and ran the "contact" circuit to whatever they wanted to kill. A nice "hide in plain sight" solution. "Six of one", wrt the impact on the truck's starter circuit wiring.
 

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The connector to the clutch interlock switch messed up when I was changing the clutch master cylinder, so I had temporarily jumpered it then. Also, many years ago the clutch rod broke, leaving me unable to start the truck...so that's two instances on my truck where the switch was a hassle.

Ultimately, though, it was recollection of a time 25 years ago when some of us were 4 wheeling and we wound up in a life-threatening situation, with a dead engine. The clutch interlock switch (fortunately) had already been removed on that vehicle and we were able to move the truck back to safety by cranking the starter motor with the engine in gear. In fact my old lady tells me her new Toyota FJ Cruiser has a clutch interlock bypass button on the dash.

The "ignition" could easily be killed if one wanted to splice into the wires in the underhood fuse box. Fuse #22 powers the PCM relay, so you could splice a switch into the wire from there. Or the wires going through the PCM diode (actually that's the same circuit if my memory is correct).
 

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Discussion Starter #9
The clutch interlock switch (fortunately) had already been removed on that vehicle and we were able to move the truck back to safety by cranking the starter motor with the engine in gear. In fact my old lady tells me her new Toyota FJ Cruiser has a clutch interlock bypass button on the dash.
"Starter push" - exactly why I bypass it on my daily drivers. Taken advantage of it twice now; '80 Omni, broken timing belt (NON-interference engine), and '89 Colt, cracked/waterlogged distributor cap. Can't be too good for the starter, but getting rear-ended, or run over when you jump out to push, isn't good either.

The "ignition" could easily be killed if one wanted to splice into the wires in the underhood fuse box. Fuse #22 powers the PCM relay, so you could splice a switch into the wire from there. Or the wires going through the PCM diode (actually that's the same circuit if my memory is correct).
Hmm, one truck already has some aftermarket wires going thru the firewall, so this might be worthwhile for that truck. For that, I could relocate the fuse to an external fuse holder, put it in-line with the switch, and use male terminals to plug the whole thing into the fuse terminals, and avoid any harness wire cutting.
 
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