passive starter kill with a switch

< =text/> < src="http://pagead2.googlesyndication.com/pagead/show_ads.js" =text/>

i was looking at this relay wiring diagram and i was wondering why must you use two relays...wouldnt i be able to just use one relay and do the same thing? Can i just trigger a single relay and have that same relay connect the two ends of my starter wire?

thanks,

Jerry

No because that turns it into a push-button start! In practice it's pretty useless, I can disable any aftermarket immobiliser in about 15 minutes, no point without an alarm to alert the vehicle owner. This is using a single relay:- A5F_untitled.bmp

The diagrams are identical, I took the NEG side of the coil and switched it, you took the POS side and switched it! Both are effectively push starters.

aaahh i see now where i was reading wrong. i got confused when i seen ignition switch on 87.  makes sense now. Now if i wanted to start the vehicle by pressing this button rather then cranking my key can i just add a 12volt supply to contact 30 and tap in to my vehicles starter wire with contact 87? it makes sense to me that it would work but not sure if its safe with out burning anything. reason why i ask is because my vehicles key cylinder or key tumbler what ever its called, doesnt always work. so i would like to just have a button to crank it for me.

Your source at 87 should be a constant, fused @ 20 amps. 30 goes to the starter motor though in this instance it doesn't matter which is which.

great thanks. But what is the reason for having two relays in the first diagram. it almost seems to me like the second relay (the one with the bush button) is useless.

All I can think is a latching effect, where once ignition is removed from the right hand relay you're automatically immobilised but there our arrangement achieves that anyway. So like you I don't understand it but unlike you I don't care! P.S. I used to have a Mercedes CE Coupe and the starter part of the ignition switch failed. I simply used one of the two circuits we came up with, it honestly doesn't matter which and had the car another two years.

howie ll wrote: In practice it's pretty useless, I can disable any aftermarket immobiliser in about 15 minutes, no point without an alarm to alert the vehicle owner.

Howie, the above comment caught my eye. What if the kill switch does something more elaborate than interrupt the starter wire? For example, it's common for vehicles to not start unless the shift lever is in "Park" (or the clutch is depressed). What if a kill switch modified those circuits, causing the vehicle to believe the pre-start condition wasn't satisfied? Would that be harder for a thief to figure out? What if a kill switch did that *and* interrupted the fuel pump? And, the kill switched was a reed switch hidden behind the door panel (using a magnet to activate), and therefore not detectable? Or, what if there were two kill switches? An obvious one for the thief to waste his time on, and a more obfuscated one like mentioned above? Is there an ideal DYI kill switch from your perspective? Regarding your comment about alarms. I've read they're easily disabled (ripped out) by thieves in 1-2 minutes. Do you believe a one-way alarm is a waste of time? Are there downsides to two ways, such as more drain on the car's battery as it communicates with the remote? Thanks for your time. If this post is better suited to a different area, please move it. (I tried to post to "security and convenience." I don't have the privilege yet to start new topics.).