boot release & universal motor.

First post here so go easy, have no electronics background and need some help understanding what is happening with my car. I have a Toad alarm and immobiliser fitted in my 89 CRX, which has an optional boot release circuit. What's happened so far: Fitted boot release solenoid to pull on boot release rod, wired perm live to correct side of motor, and earth to my alarm boot release circuit. I have been told this has worked for other people, but am now seriously thinking it should have been done with a relay. Now I get no signal at all on the boot release circuit of the alarm when pressing the correct button on the key fob, I believe the ECU is damaged on that circuit in some way (possibly because the current was too much for it to earth? From what I've since read online, activating this circuit does the following: Boot release output (on holding down button three on the radio key for three seconds, negative output of 500mA will be provided. If the alarm system is in an armed state the ultrasonic sensors and boot trigger circuit will also be disabled, and will not be re-enabled until 20 seconds after closing the boot on the vehicle) There is another circuit (with a different button) I could use to do this to avoid getting another ECU, but I want to do it right and not ruin another circuit. Here is the info from the manual, the circuit that isn't working is the Blue/Black wire - and the instructions below state using a relay. The wire I have free is the white wire, this doesn't suggest using a relay but it works in the same way (-500ma signal) Blue/Black Wire (boot release/optional output) Output signal pulls low (to ground) - connect to the coil of the driver relay for the boot release solenoid. For safety reasons this function can only be activated with the ignition off. Once activated, the boot and internal volume sensors are disabled until 20 seconds after the boot is closed. Alternatively this wire can be programmed for various outputs (press and hold button 3) see page 8-9 White Wire (variable timed output 1 second – 2.5 minutes) Connect this wire to systems that need a signal that pulls low (to ground) for an interval automatically controlled by the alarm. Once activated, the internal volume sensors are disabled until 10 seconds after the timed period. (Press and hold button 4, or programme to operate on arming). Operates with the alarm armed or disarmed and the ignition off. So a couple of questions: 1) What has been damaged by not using a relay, and why? The boot release motor did work a couple of times before the circuit stopped working completely (the boot release motor still works). 2) What relay do I need to use moving forwards, I'm thinking it has to be one that switches the powered circuit on when it gets a negative 500ma signal from the alarm wire, but switches the powered circuit off when it loses this signal (the alarm gives a 1 second pulse if programmed this way). 3) Is it possible to fix the ECU? If I test the white wire, I get a 0.6 reading on my multimeter for continuity. Thanks for your help.

You have fried the output to activate the trunk/boot release. It is doubtful you can repair it as most units aren't designed to be repaired. The output uses a transistor which will be damaged. More damage may have occurred as the solenoid draws a lot of current. You must always use a relay to activate a high current circuit. If the solenoid is grounded all the time then the 12 volt + will be switched. What you needed was a automotive SPDT relay that can handle about 30 amps. Terminal 30 and 86 of the relay should be connected to a source of battery power with an inline fuse of about 20 amps. Terminal 85 connects to the output of the alarm. Terminal 87 connects to the 12 volt + feed to the solenoid.sparky

Thanks for the reply. The alarm sends a 1 sec negative pulse, so would have earthed my universal motor for 1 second. This did make the motor pop but not strongly enough. The motor has a perm 12v to it fused at present. Can you confirm what I need to do bearing in mind the alarm switches the earth to -500ma not providing a switched live?

If the alarm output hasn't blown you're extremely lucky. The NEG (earthed via switch) side of the motor draws about 7 amps! This is for a NEG switched circuit. Use a standard Bosch type cube relay available any where, Maplin etc. 4 or 5 pin, it doesn't matter. Alarm output to 85. 3 amps fused constant 12V+ to 86. Very good ground (earth) to 87 30 to NEG switched side of release solenoid. Diode 1N4004 across 85 and 86, band to 86, this is a "quenching" diode and will prevent high voltage spark from affecting your output. You can also run a line to 85 then to a momentary switch, other side earthed to manually effect the release.

This is getting confusing now. I have a universal motor, there was no boot circuit in this car prior to me fitting one. Can I just screw the solenoid earth to body? Then fused permanent +12v to both the coil and 30 Alarm negative pulse wire to the other side of the coil Solenoid positive wire to the pin on the relay that is normally open?

Yes, I just gave you NEG switching which is better for technical reasons. No you can't just ground the solenoid body, the casing won't be a part of the circuit, that's why you have a POS (+) and a NEG (-) terminal on the solenoid. Yes to 87 and 30 being 12V+ fused at 15 amps. Then 30 to the Plus side of the solenoid, locally earth the NEG terminal.

Thanks I meant earth screwed into the car body though. I have a suitable relay in the garage so will use the white wire on a 1 second pulse instead. I'm sure the other circuit is dead.

You can test it easily enough, DMM or test light, one side to a constant 12V+, other to wire, and press the button, should show a signal after about 2 seconds.

I did this with continuity beep on dmm, nothing.

Not continuity, RED probe to 12V+, black probe to wire, meter set to 20 VDC. Much faster and more simple with a test light.