Drawing too much Current?

We all know that when connecting an output wire to the car, a relay is mandatory on wire that require a lot of current

Ex. When connecting the Domelight output wire, one must use a relay to power the domelight wire of the car.

You cannot simply connect the dome light output wire directly to the car without a relay. If you do, then the car will try to draw too much current therefore causing the brain to malfunction.

But then, some car does not require a lot of current therefore do not need a relay (Honda factory alarm disarm wire)

How do you determine if the car draws more than the output current (200mA on most alarm)

You can cut the wire and use your DMM to measure the current. If it is less than that of the alarm, no relay is required.

But this is a hassle.

I was wondering if we can simply look at a wire size and tell.

Ex. If the wire is thin (like the lock/unlock wire of the DEI alarm) can we assume that it draws less than 200mA therefore we can connect the wire directly without a relay?

Also, if a car has type A (positive lock/ unlock) and the car has negative factory alarm disarm. Can we use the neg. unlock wire and connect it to the factory alarm disarm wire?
Because when you press unlock, (on DEI alarm) the green wire sends out a positive pulse to unlock while the blue wire sends a negative pulse. Would it be safe to use the blue wire and connect it to the factory alarm disarm wire?

Has any of yall daily installer ever thought about this?

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Note: You Always Dont Get What You Pay For.

I used to just use my meter to provide the (-) pulse in parallel with the existing wire (so you don't have to cut it).

This simulates exactly what your alarm brain will be doing, and will give you an accurate reading.

So, basically, connect your black lead to ground, set your meter to A and connect your red wire to the wire you want to test.  If the reading is close to 0 then set your meter to mA and see what you have.  General rule of thumb is you don't want to go over 50% of the max capacity of the output, so if its a 200mA output you want to stay below 100mA.

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Kevin Pierson

Thanks for the input KPierson.

Does anyone else have a way of determining if a particular wire draws alot of current?


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Note: You Always Dont Get What You Pay For.

What else were you looking for?
Kevin's method is the best way, short of adding a DC current probe to your test equipment. Just make sure you're on the ground switched side of the device you're probing, and it should work just fine. If the reason you're hesitant to try it is because you don't know exactly what you're probing, put a 1/2A fast blow fuse in line with your meter, to protect it should you tap into a power source.

You should always verify that its the correct switched wire before probing it!!!!!!  haha

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Kevin Pierson

So what's wrong with the Poof ! method of testing?
Support your local fuse company..

Haha

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Kevin Pierson