domelight for overhead

I need help on wiring my domelight for my overhead dvd player in my 2012 Honda Odyssey.  I tapped into the left rear white domelight wire of the 3 pin plug (negative trigger), but I realized that it would come back on (and stay on) if I armed/locked the car.  After checking the domelight wire again, the polarity of the wire has me perplexed.

When I open a door, the wire shows 0V (ground), which suggests that it is a negative trigger domelight (consistent with Directwire and bulldogsecurity.com).  Then, when I hold down the doorpin, the wire reads about 5V (as the OEM domelights dim).  Once my Viper 5904 remote start/security system passively arms, the wire will read 12V.  This works fine for my overhead domelight.

However, if I actively arm/lock the car using either the OEM or Viper fob, the wire will only read 12V for a couple of seconds and then go to 0V.  The weird part is that the OEM domelights will stay off when I actively arm/lock the car.  Obviously, the overhead domelight will switch back on if I use the active arm/lock via OEM/Viper fob.

I tried tapping directly to the pink domelight wire under the dash, but it seems to be working fine intermittenly.  The problem is that it seems to be working mainly with the driver's doorpin (i.e. will sometimes not switch on/off for the other doors).  Also, the wire only reads 5V when the doors are closed (it never reads 12V).  Another problem with wire it to the domelight wire under the dash is that it will not dim like the OEM domelights and it shuts off sooner (the OEM domelights have a delay).

I am getting frustrated and thinking about using relays to fix the problem.  Does anyone know how I can incorporate a relay(s) to fix this annoying domelight problem?  I prefer to synchronize it with the OEM domelights (i.e. dim and delay features).

I don't understand what you are trying to achieve. Yes the door locks are negatively switched but that lead in the domelight is off a processor which will hold the dome light on for up to 1 minute or until you lock the door. If you want instant on off, tap the door open icon on your instrument panel. Frankly using a DMM with your knowledge levels is confusing you.

Howie,

What I want to achieve is the domelight on my overhead to be in sync with the other OEM domelights in my van.  My overhead has the option of choosing the polarity for the domelight.  I set it negative polarity.  When I wired the overhead domelight wire to left rear OEM domelight wire, it would be in sync with the OEM domelights (i.e. turn on, dim, and turn off at the same time as the OEM domelights).  The problem I encountered is when I physically arm/lock the van using either the OEM or Viper fob.  (The reason that the OEM works with my Viper 5904 is because I am using the datalink ADS-AL CA in D2D mode.)  When I hit the arm/lock button, the OEM domelights will turn off but the overhead domelight will turn back on (and stay on).

I don't understand the following phenomenon:

A) Why does the OEM domelight wire return to ground (i.e. 0V) when I actively arm/lock the van?  (It stays at 12V when all doors are closed and I do not hit the arm/lock button.)

B) How come the OEM domelights stay off if the wire shows ground after arming (it is negative trigger - should be at 12V)?

As I mentioned earlier, I tried to wire the overhead domelight directly to the domelight wire under the dash.  However, the problem with this approach is:

1) The overhead domelight is not in sync with the OEM domelights (i.e. it does not dim, turn off at the same time as the OEM domelights, and sometimes does not remain on if the driver's door is closed).

2) It seems to be working intermittenly (i.e. when I disarm/unlock the van using either the OEM or Viper fob, it will sometimes not turn on like the OEM domelights).

Is there a way to wire the overhead domelight to be in sync with the OEM domelights (i.e. on/off and dim) by using relays (and possibly diodes)?

In theory unless you've done something stupid wiring it in parallel with the existing domelight should work fine with no need for relays or diodes.

Like I mentioned before, tapping into the OEM domelight wire works except for one problem.  When the van is actively armed/locked (with all doors closed), the domelight wire is only momentarily at 12V and goes to ground.  Thus, the overhead domelight will turn on at that point.  Obviously, I don't want the domelight of the overhead to be on while the van is armed/locked.

I went back to check the OEM domelight wire.  Here is what I found:

OEM domelight wire:

1. 0V with doors closed and was armed/locked previously by OEM or Viper fob (OEM domelights are off at this initial point).

2. 0V with all doors closed and OEM/Viper fob used to actively unarm/unlock the van (OEM domelights turn on). 

3. 0V with any door opened (OEM domelights turn on).

3. 5V when all doors are closed (OEM domelights dim).

4. 5V with all doors closed and Viper has been passively armed (OEM domelights dim but still on due to delay).

5. 12V with all doors closed, Viper passively armed, and OEM domelights off.

6. Quick 12V pulse and then 0V if OEM or Viper fob used to actively arm/lock the van (OEM domelights are off).

Step 6 is where I run into the problem.  If the wire would not return to ground, then everything would work fine.  After work today, I will check the same sequence described above for the domelight wire under the dash. 

Right now, I have the overhead domelight wired to the domelight wire under the dash.  Last night, I did notice that the overhead domelight seems to only be working with disarm/unlock when I use the Viper fob as opposed to the OEM fob.  Right away this tells me that there is no negative pulse or trigger to the domelight wire under the dash when I disarm/unlock using the OEM fob.  It works with the Viper fob because I am using a relay for the domelight supervision wire, which is tapped to the domelight wire under the dash.

Once I confirm the polarity of the domelight wire under the dash for the sequence above, I will have to sit to think about how to get this to work with using a series of relays and likely diodes.  I know there has got to be a way.

3 wires on your add on as on the original. 12V+ constant Ground Switched Ground Correctly wired in parallel there should be no problems. End of. N.B. I've done this on lots of vehicles, never any problems, it's not rocket science.

Yes, I have done plenty of overheads before as I was an installer for Circuit City for over 5 years.  But you keep overlooking the problem that I have been repeatedly pointing out.  It returns to ground when armed!!!  So switched ground (i.e. negative trigger/pulse) will not work since it sends a ground signal when I arm the van.  You keep saying things like "in theory" and "should work".  Well, I have been trying to tell you it does NOT work.  I would not be on this forum if it was as simple as tapping into the existing domelight wire.  I clearly stated that I already tried that. 

Next time try reading more carefully before you start with the insults!

Not an intentional insult, more trying to point out that I've done this loads of times with never a problem. OK..your switched outputs which fade away such as the dome light are controlled by a timer processor. Maybe a 1N4004 diode, in line with the switched neg (door trigger) with the band towards your dome light will do the trick. I've already given you the other answer because this will be directly linked to the doors without the dubious benefits of processor control and that is to go to your dashboard/gauge cluster door open warning light. I often connect the alarm door trigger to that light, never any problems.