Piggy back main 12v 15A supply

[rsgaz]

Altering the wiring there is asking for trouble!!

Cost saving and weight saving is crazy in vehicle manufacture, every single wire is calculated to be as thin as they dare get away with! You can't just go popping an up to 15A load wherever!

Just run it to the battery, 15 amp fuse as close to the positive terminal as practical. Extend the wire with the same or larger CSA wire than the one provided.

 

[PaulBerkshire]

OK ran to battery on a 21 amp wire protected with the 15a fuse, alarm seems to work fine, added a microwave detector too which works fine in back of van. Currently i do not have lights connected, so if i wanted to get indicators to flash, where would i look to connect, at the relay? Read somewhere I could use 2 diodes one on each wire from the back of the hazard switch and just connect the single signal wire from alarm to them both.

 

[rsgaz]

each wire from the back of the hazard switch

Without a wiring diagram of the vehicle and the alarm, or actually being there, there are way too many possibilities to list of how it should or could be done I'm afraid.

For example, on a lot of Fords, the hazard switch doesn't provide a +12v output when you turn it on, nor are there two outputs. It switches the negative and sends that to the "passenger junction box", which then does the timing and switching of the relays to power the indicator lamps.

If your vehicle uses the same system, you need to know whether the wire from the alarm is a "positive output" or a "negative output". On some you can choose via a DIP switch.

You could intercept the wires that actually go directly to the lamps and use the diode trick (making sure the diodes can carry at least 4 amps forward current), but then you need to know whether your alarm can output 8 amps down that wire or does it say in the manual something like "200mA max"?