universal bypass module logic

I've done thousands of vehicles using a universal bypass module but have never attempted bypassing a vehicles anti-theft with a SPDT relay. Essentially, I know that they're pretty much the same thing. I know that the coils on the relay are hooked up to ground while running( - ignition out) and (+) ignition or (+) 12v. 87 is coiled around the transponder key then coiled around the ignition cylinder then connected to 30 on the relay using 22-24 AWG wire (87a is not used). Pretty much the same thing as a key in the box but using a different technique. So the reason I'm posting this is because it blows my mind that when the circuit is open the vehicle doesn't see the key and when the circuit is closed the vehicle sees the coded key. Why cant I just have the coded key one 1 ft or more from the barrel and start the vehicle with a non-coded cut key. How does this work? What is the theory behind this? I'm just curious and want to expand my knowledge of this topic.I drink current, eat ohms, and bleed voltage

Because the connection is not made until the relay sees both the (-) GWR and the (+) ignition. By just putting an uncoded key in the cylinder, it is not activating both "sides" of the relay coil so the over-all circuit that sends the key's RF signal to the barrel is still open (only closed by the relay).Kenny

Owner / Technician

KKD Garage LLC

Albany, NY 12205

Yeah I understand that but how does coiling the wire around the key and cylinder transfer the RF Signal? RF signal as in radio frequency signal correct?I drink current, eat ohms, and bleed voltage

From what I recall, the ring around the ignition excites the transponder in the key so that it can "read" it. Also I thought winding the coil of wire around the key creates an antenna of sorts but mostly its allowing the excitation current to make it to the key, further from the barrel.

And of course for most vehicles you could simply remove the RFI chip and glue it to the plastic antenna housing around the ignition switch but not recommended unless you're installing a UK type Cat I alarm with two circuit cuts to replace the OEM immobiliser. What Awdeclipse is saying is much safer.

How does coiling of the wire around the key cause current to flow if there is no power going through the relay? All the relay does is close a circuit. There is no power going through the wire. I know this is a electrical engineering question but I was wondering if anyone had some insight on it. @ Howe II: I'm aware that you can remove the RF chip from the key and glue it to the antenna housing but like you said I wouldn't recommend it.I drink current, eat ohms, and bleed voltage

when the car is not started remotely there is no ground on pin 85 therefore the relays contacts are closed causing 87a and 30 to be connecting when the remote start is engaged the ground when running grounds pin 85, the ign12v (or constant 12v) energizes the relay opening the contacts so that now pin 87 and 30 make connection thereby transferring the keys transponder chip signal thru the wire( makeshift antenna) to the ign cylinder which is excited by ing and reads the signal, it is a way to do so if no universal is available but i dont recommend for less than heavily qualified installers as it takes much practice to achieve proper windings( and most manufacturers require different windings) of a small gauge wire basically if your used to universals all your doing is making the antenna ring you normally place around the key cylinder with a piece of copper wire, also i highly recommend if doing the relay method to conceal that key very well in tape so that in the event of break in it is not easily found to use to start car(or use an uncut key you programmed)

Absolutely X 2 with Jim, when bored I even used to build the Velleman kit equivalent to a 528t but as a pro it isn't worth the time wasted.

I know how a relay works and what is going on with the relay when the starter is engaged. This is simple relay fundamentals. So what you're saying is that by coiling the key with wire and coiling the ignition cylinder, the wire amplifies the RF code and causes it to travel through the wire in turn exciting the immobilizer ring around the cylinder then allowing the vehicle to start?I drink current, eat ohms, and bleed voltage

The RF signals from the ignition cylinder and transponder pill in the key are induced into the wire coils. Coiling of the wire amplifies the signal just like a transformer. It is an extension of the factory antenna ring that is around the ignition cylinder which is basically built the same way.This information is provided only as a reference.

All circuits should be verified with a digital multi-meter prior to making any connections.