Loss of 12v Power


New Member
I'm a new RVr. I just bought a 2004 Allegro Bus and today I apparently accidentally set off the door alarm, I believe by opening the door before the remote had actually unlocked it. The horn began blowing, and didn't go off, even when I put the key in the ignition. After a few minutes the horn stopped, but from that point forward none of the 12 volt lights or water pumps worked.

I checked all fuses and breakers that I could locate, and none of them were blown. I reset the mains, and even reset all the DC breakers. The inverter seems to be functioning fine, as I can get 120 volts when I switch it on. But still no 12 volt power anywhere.

Any ideas anyone?


Senior Member
Loss of 12v Power

Can you start the bus? It is possible that the alarm system has some kind of shutoff in the power line to prevent starting when the alarm is tripped. If so, there has to be some kind of reset function installed (hidden switch or some sequence of steps with the available controls) to allow recovery.

If you can start the bus, it is probably not a (deliberate) alarm function. If your unit is like mine, there are fuses all over the place. There is a big one next to the inverter (for the inverter), several in the battery compartment (don't have a clue what for), a whole bunch in a compartment up front (for the vehicle functions), and a bunch next to the 120v circuit breakers (for the house functions).

If you've checked 'em all, you'll need to trace the 12v power. Start by checking the batteries, maybe they're just run down. While you are at it, anytime you check the voltage anywhere, give the connections there a look to see if they are loose or corroded. If the batteries have a good charge, check the power on the 'hot' side of the 12v fuses. I'll bet you will find no power there, since 'all' of your 12v is out. Do you have a 'house shut off switch'? If so, make sure you turn it on. If this does not help, see if you can find the solinoid this switch operates and check the input and output of that. If all the connections so far are good and the solinoid, if any, is passing power, it can be a challenge to find out where the break is.

I just got a gadget at Lowes which I hope helps me in situations like this. It is a Greenlee 'non-contact voltage detector'. I've seen similar gadgets for detecting AC, but this one claims to detect down to 5v DC. Don't have a clue how it does that, but if it does, should be great for finding breaks in 12v wiring.

Ed H.

New Member
Loss of 12v Power

Some alarm systems have a device that runs down your battery so even if a theif trys to hot-wire the vehicle it will not start. Have you checked for voltage at the chassis battery? It may need a jump start.
If all else fails, contact the alarm manufacturer and find out just how your model imobilizes the vehicle.