do all relays need to be diode isolated?

Wow - away for a day an look what happens... Just to address the questions to me...

madmanuser wrote: What could I do to test or check and see if I need a reverse biased, isolating or suppression diode?

Just fit them. Prevention is better than cure. Otherwise test by seeing if you blow something up without them (the trial&error method described before) or obtain all circuit data pertinent to your set up and determine if protection is needed.

madmanuser wrote: And would it be to much to ask you to explain how to wire these up if I do decide to add them for a little extra protection for my wiring.

Yes. Just fit them. (Not too much to ask, but it is too much to answer.) It has already been explained in this thread or at linked diagrams and threads. IMO there is no point repeating it - especially as you still seem to include the isolation function.... Just fit the diodes and be done with it. At under 20c each, why bother?

Hey good points old spark. I did some more research on this topic and it appears that using only a rectifier diode can reduce the life of the relay unless that diode is run in series with a zener. Here is the pdf from tyco electronics on this topic. http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3311.pdf Have any of you had any issues with relay life using only a rectifier diode on its own without the zener?

Yes and the average Tycho, or Bosch or Omron or Panasonic auto motive relay has an average live expectancy of about 15 MILLION cycles so I wouldn't worry too much about zener diodes. The whole point is the diode YOU need is a 1N400X. Use to differentiate inputs, example, units with single trigger for hood and trunk, since in most cases the hood pin is aftermarket, it may fail. If it does it might short out causing the trunk light to illuminate giving a flat battery. Thus diode separation. Diode across a relay, I know and appreciate what KP and Mr. I said, I just feel safer since I blew out the aux circuits on an older Clifford using a relay without a diode a few years ago. I'm with Oldspark's last post on this.

As per Howard. And from a brief peruse, it seems that article is from "the standpoint of physics". There is no mention of what reality is (ie, no statistics). And note the transient with the zenor - 25V - what does that do to a 12V circuit? Mind you, the article is about the relay and not the circuit, but why not use a 16V zenor or less instead? (Reason - it gets too complicated or the zenors will blow.) And a diode in series with a zenor? I'd really expect a better article if it were used as justification for anything. It falls far short or normal research documentation

Let's all stand back here, Mr.I, KP, Oldie and myself have all been doing this a long time and have our own methods which WORK. Our poster is asking questions from either ignorance or lack of REAL WORLD/PRACTICAL knowledge. I didn't write this post to have a hassle with KP and Mr.I, two people I respect, I would like to point our poster in the direction of asking specific questions in relation to specific problems.

Ok point taken guys. It wont be an issue. I just didn't want to hide everything and have to dig it up because a relay died due to the use of a diode without zener. But if the life expectancy is 15million cycles then your right it won't be an issue. Once again you guys FTW with all the info I need. I don't bring up articles to try and prove you guys wrong, I just want your input as to what the article says and if its really something we should consider. I respect everyone's real world experience and will hookup a diode to my relays. BUT!!!! I have a problem that arose as i was wiring everything up as a test run before final install. So I am using a DEI 451m. This unit is for the door locks, as you guys probably already know. My car is a ford mustang and uses a 5 wire door lock system. So I have the yellow ignition wire for the starter cut relay wired up to my ignition wire and it receives (+)12v from my ign wire when in run or start. What is happening is that when the ignition is turned on then off a slight click is heard in the 451m. Not sure where this feed back is coming from. The 451m has a red and purple wire that are (+)12v constants, and I have those two wires wired up to the 12v constant directly from the battery. The blue and green lock/unlock wires are connected properly to the alarm. Everything on the alarm works correctly such as lock unlock when armed/disarmed etc. Is it possible I need a diode for the (+)12v constants going to the 451m? Or is it possible power is being sent from the alarm to the 451m? Not sure what to do at this point.

Alarm is the basic viper 350. I know the alarm does have a function that locks the doors three seconds after the ignition is turn on. Maybe this sound in the 451m when the ignition is turn off has something to do with a setting in the alarm?

WOW I am a noobie. Went to my car and long behold it was unlocking the doors when ignition is turned off. Went through the menus using valet button and turned off ignition controlled locks. Thanks anyways. Onto wiring these diodes before final install..everything seems to be working great so far.

I wish I could edit posts Anyway, forgot to add a question. Thanks for your patience also! So I reversed the polarity of the parking lamps on my car because I don't want my backup battery powering my parking lamps. So I have it hooked up like this pin 85 - ground signal from alarm pin 86 - (+)12v constant pin 30 - (+)12v constant pin 87 - (+) parking lamp wire My question is where does the 10 amp fuse go? in between the (+)12v constant and pin 30 or in between pin 87 and the parking lamp wire? BTW the (+)12v constant is already fused within 12inchs of the battery. Thanks

The wire that feeds constant voltage to 30, place the fuse wherever that wire is connected to the power source.