why relays with 1 wire door locks?

I was curious, why is it necessary to use relays when doing 1 wire door locks?

Both the lock and unlock are negative, so why couldn't you just use the resistors inline with the lock and unlock wires coming from the remote start?

Almost all instructions advise you to use relays, and I have never understood why.

Thanks

Shawn

If it is just a straight negative...You shouldnt need relays...On some units with both (+ and -) outputs requires a relay ...or to boost the signal...!

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M.E.C.P & First-Class
Go slow and drink lots of water...Procrastinators' Unite...Tomorrow!

You use relays to avoid feedback on the data line..be it the 1 lock wire to the car's BCM ECU or the lock/unlock wires going back to alarm/RS brain..

Look at and older reply here: click me

The simple reason is that on most alarms with 2 wire lock outputs, they are flip-flop or TTL outputs and don't have enough available current to drive past the resistor(s). It's that simple. When you have a 6 wire output from an alarm, that means it's relay driven from the alarm and you won't need external relays.

I have had success using diodes to block the +12vdc on some cars - it didn't work on all of them. 

Using relays will guarentee 100% of the time it will work.  If you use something like a 451M (two small relays in one package) it doesn't even take up much space.

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Kevin Pierson

i have done many cars without relays for single wire system, with a diode and resistor inline.

there are only a few that i needed to use a relay.

and as Kevin mentioned, the 451m is the smallest lock relay i have seen.

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Ted
2nd Year Tier 1 Medical School
Still installing as a hobby...pays for groceries
Compustar Expert

I guess it makes sense now. Never thought of it as stopping feedback to the other components. I have always figured that a negative trigger wouldn't harm other components.

Of those of you that use the resistor and the diode, do you test it first to make sure it will work, and if not use the relays? Or is there a general rule of thumb that tells you that you will have to use relays to boost the signal? Like for instance 200ma negative is not enough and will require relays?

I have seen the 451M but never used it. I might have to try one out. What about the 456L? Is it worth adding to the collection or stick with just the 451M?

Also, whats your trick for installing the resistors inline? I just strip the wire, wrap the leg on the resistor around the wire and solder it. Then shrink wrap the hole thing. Is there a better way to do it? I am always worried that the connection is not very sturdy and could break when I am tucking wires away. The solder joint is stiff, but I don't solder all the way up the leg. I try to keep about an 1/8" gap from the resistor so my solder connection doesn't burn the resistor.

Thanks for the info. Maybe I think too much when I am installing. I am always looking for the little things and tricks others use to make the installs quicker.

Shawn

i have always tried it as is without relays. If it works then it works. If not, i will wire up a relay.

the 451 is the newer and smaller version of the 456l. Just keep 451m on hand if you install often.

i will use the lock or unlock output, place a diode and resistor inline one after another. Solder them, and on the other end, i solder an additional 5 inches or so of wire to the end of the resistor, and that will go to the car wire. makes it abit cleaner to install

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Ted
2nd Year Tier 1 Medical School
Still installing as a hobby...pays for groceries
Compustar Expert

Good Info.

Thanks for the tips.

Shawn