Club 80-90 Forums

Have an old type alarm fitted (moss) which used to activate the indicators when armed and disarmed. Connections are ok and other elements of the alarm work ok. I have checked the voltage when arming and the output from the unit fluctuates around 7 - 8v but does not switch the indicators on and off, I have also tested with a bulb which does not light up when armed. If I use a 12v 30 amp relay into the system will this create the extra voltage to flash the indicators. Posting this before testing as do not want to cause any damage.

Use the alarm to energise the relay which then flashes the lights?
Won't do any harm but might not work depending on what's wrong with the alarm.

Yes thanks that's what I'm hoping, hopefully the voltage from the unit will be enough to energise the relay and flash the lights.

You would need a 6V relays. 12V relays struggle to pull in at around 7V although they will hold in down to around 5V. If you are switching the indicators you will need two relays one to switch each side, or a single relay and wire each side through diodes.

Just use a step-up converter on the output from the alarm. But if you have isolated the indicators and then tested the output with a single bulb and the bulb didn't work there will not be enough current to do anything with and you will need to repair the output of the alarm. (or replace it )
Presumably you have checked the earths for the alarm haven't gone high resistance.

My thinking is its dropping 5v when connected to a bulb, a relay will draw circa one tenth the current of the bulb if the bulb is e.g. 21w, so may only drop a half volt or so - so relay may work OK.