Printer Friendly Forum Posts - Domelight Supervision Not Triggering Relay

So I'm installing an avital 5303L into a 1981 cherokee. I've got every function working properly except the domelight supervision. My car's domelight is a single terminal negative trigger. I ran the 200ma negative signal from the alarm to pin 85 on the relay. Pin 86 is 12v constant, pin 87 is ground and 30 is to the domelight wire. I cannot for the life of me get the alarm to trigger the relay. I have verified the alarm is sending a negative signal with a volt meter. I even tried adding a transistor based on a diagram I found here but still no luck. I'm at a loss at this point and this is the last piece of wiring for me to complete. Please help.

Pic 1 is my first transistor circuit attempt that did nothing. posted_image

Pic 2 is my second circuit attempt but using the transistor to trigger the positive side of the relay. Still nothing. posted_image

Guess I should mention I have verified the relay works and tried two known functioning relays.

Also, like I mentioned the keyless entry works, the remote start works, the shock sensor works...all of it works but the stinking domelight and it's killing me.

Adding a better pic of circuit 2 since it was so dark. posted_image

Is it a 1981 Chief or 1991 Cherokee?

What color is the output wire from the alarm brain that you are using?

What color wire are you connected to in the Jeep and where are you locating the wire? Is it the same wire you are connected to for door triggers for the alarm?

How did you manually test the relay?

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Steve G

Notice that all connections on my diagram are negative. Negative from alarm brain, ground to center conductor or case of transistor and ground output from the emitter. You need to ground the center leg and apply power to 86 of the relay.

iskidoo wrote:

Is it a 1981 Chief or 1991 Cherokee?

What color is the output wire from the alarm brain that you are using?

What color wire are you connected to in the Jeep and where are you locating the wire? Is it the same wire you are connected to for door triggers for the alarm?

How did you manually test the relay?

The Chief was a package on the original Cherokees. It's a 1981 Cherokee with the Laredo package (electric locks and adjustable mirrors...fancy :D) .

The alarm output wire is black with a yellow tracer.

The domelight wire is black and directly connected to the single terminal door jamb switch. I do not currently have the alarm's door trigger wire (green) connected as I try to resolve this issue. At first I did have the two wires (black w/yellow & green) connected together and run to the cherokee's domelight wire.

I had the relay wired as listed in the previous post but instead of pin 85 going to the signal wire I directly grounded it to a body ground.

i am an idiot wrote:

Notice that all connections on my diagram are negative. Negative from alarm brain, ground to center conductor or case of transistor and ground output from the emitter. You need to ground the center leg and apply power to 86 of the relay.

I tried that setup and it did not work for me. It's actually the first thing I tried.

Edit: if that's the solution that's worked I'll give it another go. I'm still not sure how a transistor is working with only grounds operating it since the data sheet suggests it works off a voltage differential but I'm far from being an electronic wizard. I'm barely a hack and I'm sure y'all know infinitely more than myself. :D

At this point I'm ready to try any solution as I just can't seem to figure it out and that bugs the crap out of me.

When you tied the 2 wires directly to the door trigger it's likely that you may have damaged the dome light output. You say you tested it for a negative output.

proper way to test for a (-) signal in a normal +12 volt vehicle with a Digital Multimeter is as follows.
Set DMM to 20 volts DC range
Connect Red test lead to +12 volt constant source
Connect Black test lead to suspect wire
When the (-) signal is present, the DMM will show +12 volts. Kind of inverse logic but it works. [from user Kreg357]

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Steve G

I did exactly as you said and get 12v reading on the dmm. I can see when the alarm sends the signal and when it turns off after 30s.

Is it a typical aftermarket spdt 12 volt automotive relay? If you trigger it using the trunk output does it trigger the relay as it should?

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Steve G

iskidoo wrote:

Is it a typical aftermarket spdt 12 volt automotive relay? If you trigger it using the trunk output does it trigger the relay as it should?

Yup regular ol autozone relay. 30amp 5 pin relay.

I'll try the trunk lead tomorrow when I'm in the shop. I also ordered an ssr that should require less power to trip that I'm hoping arrives tomorrow.

The TIP42 in Pic 1 is a PNP transistor. Pic 2 shows a circuit for an NPN transistor so won't work with the TIP42.

eguru] wrote:

The TIP42 in Pic 1 is a PNP transistor. Pic 2 shows a circuit for an NPN transistor so won't work with the TIP42.

How is 2 positives and a single negative a npn circuit? Pic 2 is based off of the data sheet images I dug up. I'm new to this level of circuitry so I don't doubt I did it wrong I'd just like some more explanation as to what it is I goofed up.

Edit: Do I need to reverse the collector and emitter?

Have you tried contacting the seller to swap out the unit?

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Steve G

iskidoo wrote:

Have you tried contacting the seller to swap out the unit?

I already cut all the unused wires so it's not really an option. Not to mention, based on what my dmm says, the alarm is functioning just fine. Yet something is amiss.

That diagram works. It has been used many times. Take a picture of your setup and post it.

rooney77 wrote:

eguru] wrote:

The TIP42 in Pic 1 is a PNP transistor. Pic 2 shows a circuit for an NPN transistor so won't work with the TIP42.

How is 2 positives and a single negative a npn circuit? Pic 2 is based off of the data sheet images I dug up. I'm new to this level of circuitry so I don't doubt I did it wrong I'd just like some more explanation as to what it is I goofed up.

Edit: Do I need to reverse the collector and emitter?

NPN and PNP are used to describe the fabrication (the doping of the individual silicon structures) of the transistor and do not refer to the polarity of the external connections. In Pic2, the Base needs to be positive wrt the Emitter so that current can flow from the Collector to the Emitter. Since the alarm feed to the Base is ground when active, the NPN transistor won't turn on.

Pic 1 with the TIP42 (PNP transistor) should work - although I would like it better if there was a 120 ohm resistor in series with the Base lead.

So I connected the transistor in the same manner as pic 1. It's ghetto I know but I'm trying to be sure it all works before I final wire it. Also, you're looking at the backside of the transistor.

After connecting the transistor I put the black lead of the dmm on the signal into the relay (85) and the red on the constant 12v (86). When the alarm is unlocked I got voltage (2v for some reason, straight from battery) and it was there for 30s as expected. Relay did not trigger though. With the 12v constant and signal connected only to the dmm I'm seeing the full 12v.looks like there's a significant voltage drop in the resistor.

Yes I know it all looks like crap right now but the 3rd pic shows what it will look like, that's my door lock replays. posted_image

Checked my other resistors and I see that same voltage drop so I assume it's normal.

The trunk release lead does trigger the relay.

Is there a way to measure the strength of the signal from the alarm?

eguru] wrote:

rooney77 wrote:

eguru] wrote:

The TIP42 in Pic 1 is a PNP transistor. Pic 2 shows a circuit for an NPN transistor so won't work with the TIP42.

How is 2 positives and a single negative a npn circuit? Pic 2 is based off of the data sheet images I dug up. I'm new to this level of circuitry so I don't doubt I did it wrong I'd just like some more explanation as to what it is I goofed up.

Edit: Do I need to reverse the collector and emitter?

NPN and PNP are used to describe the fabrication (the doping of the individual silicon structures) of the transistor and do not refer to the polarity of the external connections. In Pic2, the Base needs to be positive wrt the Emitter so that current can flow from the Collector to the Emitter. Since the alarm feed to the Base is ground when active, the NPN transistor won't turn on.

Pic 1 with the TIP42 (PNP transistor) should work - although I would like it better if there was a 120 ohm resistor in series with the Base lead.

Thanks for the info. I appreciate you explaining it.

The output is damaged. If you wont get the seller to swap the brain then I think you would be better off just replacing the brain only. The cut wires aren’t really an issue since you would just keep your installed wires intact and send the brand new wiring harnesses back with the defective brain unit. If you buy just another brain unit then it’s about $40 or cheaper if you make an offer. I just searched eBay for 5x05 Avital and found one.

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Steve G

So I agree it's likely damaged but what I can't figure out is how it's still sending a signal. I checked the ma reading on the trunk signal and got 0.14ma and the dome signal got a 0.12ma reading. I just keep thinking I can make it work. Admittedly I'm a bit retarded at times though. :D

Alright so an interesting finding. With the transistor wired like pic 1 and the relay all setup correctly I unlocked the alarm and was checking for continuity across the collector and emitter. In the process I accidentally bridged the base (currently receiving signal) and the collector. Low and behold the lights came on and stayed on until the signal quit after 30s.

So I tested that again by unlocking and immediately bridging the two and got the same result. So the signal is strong enough to keep the relay triggered but not strong enough to trigger it initially.

Needs about 130mA to trigger and you tested 120mA. The trunk gave you just enough to trigger but in reality they should all be putting out about 200mA. Just for the hell of it double check that you have the unit connected to a good solid ground. Scrape away any paint if necessary.

https://www.mobileinformationlabs.com/How%20To%20Guides/Relays/HowTo-Relays_understanding_Intro.htm

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Steve G