Anyone up for a game of Name That Part?

[f-two-fiddy]

This is installed right behind the pass side battery. I traced the output wire to the cab. Where I assume the PO had a brake controller installed. I've never seen one these units before.

What Is It?

 

[The Warden]

Looks like an isolator to me...there was a smaller one in my truck when I first got it, but the diode had blown out. It was wired so that the alternator could charge the truck batteries as well as the 12+ feed to the trailer plug, but the trailer batteries couldn't discharge the truck batteries...

 

[f-two-fiddy]

Huh, This thing has power, even when the Alt is not turning.

 

[The Warden]

So did mine, because the other side was hooked directly to the battery (well, it went to the battery terminal on the starter relay, but same thing)...IIRC, juice could flow from either battery terminal to the alternator terminal in both directions; just, juice couldn't flow from one battery terminal to the other.

I could be remembering wrong, though; it's been a while, and I'm a little preoccupied still trying to figure out what happened with my controller *sigh*

 

[krawlr]

Looks like an isolator to me too. Normally they have 1 input from the alt and 2 outputs, 1 for the main batt and one to the aux batt. Then the aux batt can be drained without killing the main. Where do the red wires go?

 

[f-two-fiddy]

I installed them. The previous ones were fried. They were only 8ga. One goes to the alt output, the other is spliced into factory wire that used to go to the alt output.

 

[OkieGringo]

That's called a dual battery isolator. The alternator will charge both batteries connected to it, but the trailer/aux battery cannot draw/suck juice from the engine battery nor can the truck battery suck juice from the Aux battery. You should take it off and send it to me cuz they are friggin' expensive(around $100 for a high amp unit) and I can't afford one . OkieGringo

 

[krawlr]

So the connection going in the cab isn't connected now? If you don't need that second output I would eliminate that thing. The solenoid type dual batt systen that Painless sells is more reliable IMO if you want an aux batt.

 

[Mr_Roboto]

That's an old-style battery isolator. The problem with those is that you have an @ .7 volt drop across the diodes. They work OK with an externally regulated alternator, but you end up with low charging in you have an internal regulated alternator. I tried one of those and didn't get enough voltage to do what I needed. Ended up going with a constant duty relay (sold on eBay as stereo relays).