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Discussion Starter #1
I recently installed a dual battery using Anderson connectors and a True Am Isolator. I have some lights hooked up to the auxiliary battery. Can someone please tell me why they lights don’t work when i have the batteries separated (meaning i disconnected the andersons). Why won’t that auxiliary battery work in a standalone fashion? I hope that I phrased the question clearly.

thx and happy new year.
 

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Good question. the lights are part of the topper i just had installed. so i'm "guessing" they are grounded to the body in the rear of the truck. the only wire that goes to the auxiliary battery is the red positive. i'll look for sure but you think that's it? i'll look for sure. Thx
 

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Good question. the lights are part of the topper i just had installed. so i'm "guessing" they are grounded to the body in the rear of the truck. the only wire that goes to the auxiliary battery is the red positive. i'll look for sure but you think that's it? i'll look for sure. Thx
1) Following up on the ground question, is the second battery ground run to the truck body or does the ground just run to the primary battery -- that is, do you have no ground connection when the second battery is isolated?

2) Is there a switch for the lights and is the switch run to a relay that is taking keyed power somewhere -- that is, are you sure it's a disconnect or is it that you don't have power to the switch because it's keyed and you are only isolating the battery when the truck is off?
 

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1) Following up on the ground question, is the second battery ground run to the truck body or does the ground just run to the primary battery -- that is, do you have no ground connection when the second battery is isolated?

Second battery ground runs back to primary...so i have no ground connection when the second battery is isolated. I guess this answers my original question?

2) Is there a switch for the lights and is the switch run to a relay that is taking keyed power somewhere -- that is, are you sure it's a disconnect or is it that you don't have power to the switch because it's keyed and you are only isolating the battery when the truck is off?

Yes, there is a switch for the lights but not taking a keyed power. Lights work without key.
 

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1) Following up on the ground question, is the second battery ground run to the truck body or does the ground just run to the primary battery -- that is, do you have no ground connection when the second battery is isolated?

Second battery ground runs back to primary...so i have no ground connection when the second battery is isolated. I guess this answers my original question?
Maybe. I don't know that isolator, but if it's isolating both the positive and negative, that's the problem -- seems strange that it would, but without seeing it I can't think of any other reason it wouldn't work when the batteries are isolated and the positive is direct to the battery. With the battery isolated and the lights on just touch a wire from the aux. negative to ground and see if the lights go on -- if so, it's a ground problem at the battery. Maybe someone else will weigh in, but if that's the issue I don't see any reason that you can't run a ground from the aux. battery to ground in addition to the primary battery -- you can get short 0/1 gauge cable for that.

If it's not a ground issue at the battery the only thing I can think of is that the power to the switch that's running the relay is somehow getting cut off when the battery is isolated. Hard to imagine without seeing it, but if you've got a meter, check for power at the switch with the battery isolated.
 

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Good question. the lights are part of the topper i just had installed. so i'm "guessing" they are grounded to the body in the rear of the truck. the only wire that goes to the auxiliary battery is the red positive. i'll look for sure but you think that's it? i'll look for sure. Thx

Just remember, for any DC circuit to work, it needs both positive and negative and they both need to be connected in some manner. Sometimes a pencil drawing of what you have can help you to visualize what you have.
 

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Discussion Starter #8
With your help, i think i figured out the problem. The "2nd battery ground" question got me thinking. I'm pretty certain i followed isolator instructions to the letter (which shows the 2nd ground connecting to the 1st ground). But...i found other documentation that looks to be more correct (which runs the ground to the body vehicle)

Sketch is attached.

Time to reconnect. Will circle back with the results.
 

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Discussion Starter #9
No dice. disconnected the battery and the lights go out. I put a meter to the battery and get 12.7 V connected and disconnected. Which leads me to believe the lights to the topper aren't grounded properly?
 

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No dice. disconnected the battery and the lights go out. I put a meter to the battery and get 12.7 V connected and disconnected. Which leads me to believe the lights to the topper aren't grounded properly?
You said the switch runs a relay. I would check for power at the relay. Is there power going to the power side of the relay - should be power there under all battery scenarios as that is direct to the battery? Is there power going to the switch side of the relay with the cap light switch on - if it's not keyed power it should be powered under all conditions if the switch is on?

Sent from my SAMSUNG-SM-G891A using Tapatalk
 

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Discussion Starter #11
I'm not sure i said the switch runs a relay. All I have, that i can see, is a Red Wire that runs to the battery. That said, I'll have to trace it back into the cap. The cap has three independent sets of lights (2 sides and the rear) and they operate independently. Thx again for the troubleshooting help.
 

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I'm not sure i said the switch runs a relay. All I have, that i can see, is a Red Wire that runs to the battery. That said, I'll have to trace it back into the cap. The cap has three independent sets of lights (2 sides and the rear) and they operate independently. Thx again for the troubleshooting help.
Wait, I reread your first post. I was thinking you were just talking about it not working when the battery is isolated using the TrueAm. But you are talking about disconnecting the aux battery by disconnecting the Andersen Connector. If the only ground goes to the Andersen and if you disconnect that you are disconnecting the ground on the aux. battery. So yeah, that's the problem. If you want to disconnect the Andersen and still use the battery, you're gonna have to have a separate ground from the battery to the truck -- you can still have the ground go to the Andersen so it connects to the main when it's attached, but if it isn't separately grounded to the truck it isn't going to do anything when the Andersen is disconnected.
 

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Discussion Starter #13
Well...I feel like an idiot. Thx for the help.

But I do have a question: can I run an additional ground directly from the second battery?
 

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No dice. disconnected the battery and the lights go out. I put a meter to the battery and get 12.7 V connected and disconnected. Which leads me to believe the lights to the topper aren't grounded properly?
Where are you getting 12.7 volts connected and disconnected? Are you simply checking at the battery posts?

I would verify where the topper lights are grounded. Also, are you checking continuity on the circuit in question?

Side note, which wires are you disconnecting with the andersen?
 

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Well...I feel like an idiot. Thx for the help.

But I do have a question: can I run an additional ground directly from the second battery?
Shouldn't be a problem. Ideally you want a good 0/1 gauge ground cable. Local auto supply may have something that will work. There's also a guy in Duluth that makes them to size and termination as requested on eBay -- see here. Not sure how close that is to you, but shipping is free.
 

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Discussion Starter #16 (Edited)
Where are you getting 12.7 volts connected and disconnected? Are you simply checking at the battery posts?

Yes. that is what i did

I would verify where the topper lights are grounded. Also, are you checking continuity on the circuit in question?

Agreed. Need to trace this when I've got some time, and temps to work in. See below.

Side note, which wires are you disconnecting with the andersen?
As i think about this more, this is still puzzle. The anderson connectors disconnect the second battery positive and negative. that said, the topper light wire is connected directly to the positive on the second battery...which goes back to having to track the grounding of those lights.

Shouldn't be a problem. Ideally you want a good 0/1 gauge ground cable. Local auto supply may have something that will work. There's also a guy in Duluth that makes them to size and termination as requested on eBay -- see here. Not sure how close that is to you, but shipping is free.
I work near duluth. I have plenty of 2 gauge left from the battery install. Thx for the help.
 

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Well...I feel like an idiot. Thx for the help.

But I do have a question: can I run an additional ground directly from the second battery?
Yes you can and should. It will still disconnect with the Anderson, but still be grounded so that anything with the positive connected to the battery will still work.
Good luck
Oh and your pic doesn't work!
 

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As i think about this more, this is still puzzle. The anderson connectors disconnect the second battery positive and negative. that said, the topper light wire is connected directly to the positive on the second battery...which goes back to having to track the grounding of those lights.
Nope, as Hotrod indicates below, you are removing the ground for the battery when you disconnect the Andersen. Think of it this way. You have to have a complete loop from the battery positive back to the battery negative to create a circuit. The most basic circuit would be: (a) Battery + terminal, (b) a wire going from battery + terminal to lightbulb wire in, (c) lightbulb filiment, which lights up, (d) wire going from lightbulp wire out to out to Battery - terminal. You have a complete loop from Battery + to Battery -.

What you have: (a) Auxiliary Battery + terminal, (b) wire from Auxiliary Battery + terminal to lightbulb wire in, (c) lightbulb filiment, (d) wire going from lightbulb wire out to truck frame, (e) wire going from to truck frame to Primary Battery - terminal, (f) wire going from Primary Battery - terminal to Andersen Connector, (g) wire going from Andresen connector to Auxiliary Battery - terminal. That's your complete loop.

When you disconnect the Andersen connector you are breaking the circuit loop at the (f) to (g) stage. The fact that you have ground to the primary battery is irrelevant.

If you run a ground from the Auxiliary Battery - terminal to the truck then steps (e) through (g) above are covered by the wire going from truck frame to Auxiliary Battery - terminal. Then the Andersen connector doesn't play a role in whether the lights connected to the Aux battery go on.
 
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