aux battery for 1998 k1500 question

[wildncrazyguy]

Looking for some understanding here how this is supposed to work. I'm pretty sure I have it hooked up like the diagram says, but I get no charging to the aux battery. I'm pretty sure the relay isn't opening or closing more likely to be technical about it, and that's been my misunderstanding all along while I was piecing this together and trying to find someone with the same configuration.

My question is in this configuration, what is the trigger for the relay? The relay has a connection to the starting battery through the cable that powers the underhood fuse box (10) and a connection to the aux battery (1). The only thing I found online regarding how it's supposed to work is when you turn the key on it triggers the relay, when in starting mode it cuts out aux battery and when key is off it cuts out aux.

I still don't know how the fuse box connection would send to the relay that the key is on/off/starting. Seems it's just a connection from one battery to the other with a relay in between and currently it's off and nothing to turn it on. Hope that all makes sense. Thank for anyone who knows how this works that can provide a little insight. They really don't show you a great picture at all. I'm sure there is a document on how to wire the 8y8 option (I think that is this case), but my two GM dealerships don't have a clue and I keep coming up with the same picture on the web. To be sure there is a service manual or document regarding the issue, in case someone came in with a factory hookup and they had to work on it...

Again, not sure how the key operation triggers the relay or what would trigger the relay in this configuration. I get alternator 14+ on the top post of the relay and only 12.48 on bottom post to the aux battery. The aux battery reading at the terminals is 12.48. So alternator power is getting to the relay, I just think it's in the open position and needs to trigger closed to complete the circuit to flow through to the aux. battery.

It COULD be a bad relay, although new, and it magically works when the key is positioned on, but I don't know how it would get the signal the way it's configured.

Here is what I'm working on. Any help is MUCH appreciated. Thanks!

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[SAATR]

Is the trigger wire hot when the key is in the run position and open when it's starting and off? If so, you have a bad solenoid or a ground issue with the relay. Those relays ground through the base, so I would check continuity from the base to battery ground. If it's an open circuit, run a wire from the base to one of the body grounds or get to bare metal where it contacts the fender for a better connection. If the trigger wire does not act as described then you have it on the wrong circuit.

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[wildncrazyguy]

Is the trigger wire hot when the key is in the run position and open when it's starting and off? If the trigger wire does not act as described then you have it on the wrong circuit.

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Trigger wire? I agree there SHOULD be something that tells it to open or close. That's probably the issue somehow, but I don't see how a trigger wire fits into the wiring diagram. There's only two post , well three on the relay, but the ground is not used and I did check that the relay grounds properly and is firm to the fenderwell. The top post on the relay is the hot wire from the main battery which is connected to the underhood fuse panel and gives power to the PCM and everything else, not a particular circuit, see pic. There's a pigtail with a fusable link that comes off the fuse panel connection to the relay top post. The bottom post is the hot wire directly to the positive post of the aux battery. I'm missing something. Hoping someone who has dealt with k1500 dual battery factory setup in this application finds this thread... Thanks.

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[SAATR]

Whole thread on the subject from another board, replete with wiring diagrams. You'll have to tie into the truck's harness for the trigger wire that I spoke of. It is powered off of fuse 24 in the IP fuse block, which is hot in the run key position, as I said. If your truck wasn't spec'd to have the camper or police packages, then you will have to tie a wire into the factory harness to power your relay.\

Here's the link so you can look at everything that was posted:

http://67-72chevytrucks.com/vboard/showthread.php?t=600724

 

[mattillac]

Howdy, FWIW my 1999 k2500 does have this setup.

......My question is in this configuration, what is the trigger for the relay? The relay has a connection to the starting battery through the cable that powers the underhood fuse box (10) and a connection to the aux battery (1)......

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.....There's only two post , well three on the relay, but the ground is not used......

If I am reading correctly, the confusion may be that third post(smaller one)on the front of the relay. That little post should be the "trigger" connection / the "hot in run only" switched power source should connect there. The relay should need three wires, the two bigger ones are for the aux battery/fuse center and one smaller wire is for the "trgger". The relay should obtain the ground from its metal base which has already been noted.

There may be continuity to ground if you test/meter that small post, but that would probably yield a high resistance reading(instead of zero ohms)due to the small electromagnet or whatever is inside that relay(between the small post and ground) .

As mentioned, that trigger wire should come from the instrument panel fuse #24 4WD 25AMP, which should be hot in run only. That same trigger wire should connected to the small post on the front of that relay.

Best of luck.

Edit: Pics of my 1999 aux battery relay.

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[wildncrazyguy]

Awesome. I did run a test brown wire temporarily from fuse 24 to the small tap on the relay and works perfect! Now I have to see the best way to fish a wire through from the engine compartment to the inside fuse box. I already have a hole that may work, but I also need to run a couple of wires for a brake controller I'm wiring to my 7 pole in the rear. I've got the orange and blue wires up from underneath the brake booster. What moron decided to hide them in a place where you can't get to??? Anyway have the orange connected to the fuse box and need to run the blue into the cab and a couple of wires back out for the brake controller so I guess I'll be working on that as soon as possible and run all my wires through this hole and grommet at that time. I have the stuff, just need the time.

In any case, thanks to all. It makes perfect sense now, but the drawing I was working off of didn't refer to any trigger wire. I guess that was a whole different wiring diragram. Thank you.

 

[meterman]

Looking for that ever elusive left side battery tray so I can do this mod anyone have any leads ?


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[meterman]

Got one now


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