I want to install two battery gauges in my dashboard, one for the engine battery and one for the house batteries. The charge/discharge gauge in the instrument cluster no longer works.I could just wire the gauges directly to the batteries, but then they would be on all the time. I would rather have them on only when the ignition is on.I have bought a 12VDC relay that I can use to ground both gauges, and then run the hot line from the gauges to each battery. Thus the relay, when energized, will turn on the gauges.What do I tap into on the fuze box that will energize when the ignition is on?Is there an "accessory" port or something? I think there is a fuse place for power windows (this only has crank windows), and I think those only work when the ignition is on, or they used to back in 1990. Maybe I could jack into the power window port?Steve

For controlling the relay, use anything that only works with the key onMaybe the radio? Heater ?

Sometimes a cig. lighter outlet will be switched, you could tap into one of those.Otherwise you'll need to probe until you find what you need.

Two gauges, two relays or a single relay with double pole single throw contacts. There is no other way to access ignition signal to feed separate gauges.There is ignition A and ignition B circuitsA is on even when cranking the engine (such as engine ignition)B shuts down when the engine is being cranked (wipers, heater, radio)

This really depends on the model. I did a lot of research when I wanted to do something similar with my Sprinter. Found some vehicles have a switched connection on the fuse panel. Some don't. Finally plugged an extra wire in with the ignition switch line. This runs to a relay so not a lot of draw. Somebody said it best. Take your meter and poke around.

For the Ignition on lead you can pick up power from the dash radio lead, Or the aux panel (if you have one) your battery control center (Should have spare fuses marked IGNITION) or chassis main panelFor house batteries you can use a relay powered by the above wire you tapped.That is the best I can do.

How to get power only when ignition is on? | Good Sam Community

15 Replies

wa8yxm
Explorer III
Jun 25, 2015
For the Ignition on lead you can pick up power from the dash radio lead, Or the aux panel (if you have one) your battery control center (Should have spare fuses marked IGNITION) or chassis main panel

For house batteries you can use a relay powered by the above wire you tapped.

That is the best I can do.
sprintstream
Explorer
Jun 25, 2015
This really depends on the model. I did a lot of research when I wanted to do something similar with my Sprinter. Found some vehicles have a switched connection on the fuse panel. Some don't. Finally plugged an extra wire in with the ignition switch line.
This runs to a relay so not a lot of draw. Somebody said it best. Take your meter and poke around.
MEXICOWANDERER
Explorer
Jun 25, 2015
Two gauges, two relays or a single relay with double pole single throw contacts. There is no other way to access ignition signal to feed separate gauges.

There is ignition A and ignition B circuits
A is on even when cranking the engine (such as engine ignition)
B shuts down when the engine is being cranked (wipers, heater, radio)
ScottG
Nomad
Jun 25, 2015
Sometimes a cig. lighter outlet will be switched, you could tap into one of those.
Otherwise you'll need to probe until you find what you need.
MrWizard
Moderator
Jun 25, 2015
For controlling the relay, use anything that only works with the key on
Maybe the radio? Heater ?

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How to get power only when ignition is on?

15 Replies

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