Power tap in a dual battery truck?

[tbk5]

I want to install a mobile transceiver in my pickup (05 GMC 2500). I understand the reasons for connecting the power leads directly to the battery. This truck has dual batteries. Do I just pick the most convenient one? How do I determine which is the primary (look for the one connected to the starter?) vs the secondary battery? My understanding is that the secondary is used for accessories. I am probably overthinking this but I really don't want to fry anything. My search of the interwebs only comes up with info to install a second battery. Any insight is greatly appreciated.

 

[Chet0729]

Generally one is isolated when the truck is not running if it is a camper package. Depending on the setup they may just be in parallel. A lot of diesels are setup like this for extra cranking power. I would connect it to the one that is connected to the starter. Be sure to fuse the wire as close to the battery as possible.

 

[millbilly]

What kind of radio are you installing? Wattage? Does it have an ignition sense or just the one power wire and ground?

 

[stinger35]

In line fuse if your coming off the battery is in your best interest.

 

[tbk5]

A Kenwood TM-V71. Just a positive and negative lead.

Power requirement: Receive, 1.2 A (2 W audio); transmit, 13 A (max).
The transceiver has 15A fuses and the power leads have 20A fuses.
RF Output is 5, 10, or 50W

It is a diesel.

 

[edhead35]

I just did a temp install off of a tap a fuse in the fuse panel but get alot of engines noise. Doing the real install this weekend. Great radio. I would run it off the main battery if you are unsure how they are wired. If you are certain that the second battery is isolated and the charging method matches your style I would love to have a second battery for the HAM. In my case I am just putting a bigger main deep cycle battery instead of spending the money on a dual.

 

[tbk5]

I found a schematic in the service manual. View attachment Battery Schematics.pdf
The left battery is primary and the right is the auxiliary. I think I will connect directly (fused) to the primary. I could use the junction block as well for the positive lead. It does look like the batteries are isolated via a relay.

I found some good information here: http://k0bg.com/wiring.html

 

[edhead35]

If the secondary battery charges automatically and then isolates again, and it is a battery that can be drained and recharged without ruining it like a deep cycle , some run it to the secondary so they can run accessories with the engine off and not worry about discharging the primary starting battery which usually cannot handle being discharged and recharged too far.

 

[Miamivice]

In the chevy/gmc the battery just in front of the glove box is the primary, front left out by the headlight it the aux. Battery, wire to that one, and make sure it's fused

 

[tbk5]

If the secondary battery charges automatically and then isolates again, and it is a battery that can be drained and recharged without ruining it like a deep cycle , some run it to the secondary so they can run accessories with the engine off and not worry about discharging the primary starting battery which usually cannot handle being discharged and recharged too far.

In the chevy/gmc the battery just in front of the glove box is the primary, front left out by the headlight it the aux. Battery, wire to that one, and make sure it's fused

thanks to all.. This sounds like the plan. Both the pos and neg leads are fused with 20A fuses. There is a second 15A fuse on the pos lead at the transceiver.