What is it for? Firewall relay/solenoid
 

On the passenger side firewall of an 05 2500hd. The truck was already mostly stripped when I got it. It only has one wire left on it that appears to go down to the starter...

Thanks in advance!

Re: What is it for? Firewall relay/solenoid
 

its a starter soionoid but shouldnt have been on that truck for the starter

Re: What is it for? Firewall relay/solenoid
 

Could be dual battery isolator solenoid thing. I have one similar on my 86. Previous owner installed extra battery in bed of truck for over cab camper.

Similar to started solenoid but different.

Re: What is it for? Firewall relay/solenoid
 

That was my first thought, but I came up with nothing on a search.

What baffles me is the factory studs. Painted red (just like the truck), looks like all the others but I have 6 other 99-07 trucks including 03, 06 and other 05 and none of them have these 2 studs.

Re: What is it for? Firewall relay/solenoid
 

It is the factory relay for a dual battery setup

Re: What is it for? Firewall relay/solenoid
 

I finally figured out that yes it is for a dual battery setup, but more specifically a camper special package dual battery isolator.

Re: What is it for? Firewall relay/solenoid
 

i was gonna look under the hood of mine today to see if there was lugs, just for the desire to know.

I was thinking that if your truck is a HD version it might have the dual battery isolater as well since I THINK the HD versions all had diesel options? just a thought.

-Izzy

Re: What is it for? Firewall relay/solenoid
 

This one is a 6.0... The kicker is someone removed the second battery tray and put the fender brace in, so it 'looked' like it didn't have the dual battery option.

Re: What is it for? Firewall relay/solenoid
 

Probably a car lot changed it over to save having to buy another battery. They do that crap around here all the time. I deliver used car and truck parts, car lots and body shops are our biggest customers...

The 04 2500hd I bought a few months ago came with 8.1, it HAD dual batteries when I looked at it and bid on it (impound), web it arrived at my shop everything 'dual' was missing, the tow truck driver apparently thought he needed it more than he thought I did. Bastard.