A Matter Of Grounding

Wayne02 · June 17, 2010

2000 GMC sierra slt, ext cab, 6L, 4wd, NBS, w/ trailer package.

I'm in the process of installing the factory aux battery option #TP2 in this truck using all factory parts, and I am complete with the job except for one issue. This set-up isolates the aux battery while in use but runs it in parallel with the start battery while the truck is running so that both start and aux battery get charged. The idea being you can power your camper from the aux battery all weekend without fear of running down the start battery and not be able to start the truck when it's time to go home.

I've run into an issue with finding a ground for the aux battery negative cable. This is a factory cable so of course it is of a specific length.

It is my understanding that this aux battery negative cable is supposed to be terminated on the block at Ground 106 in Zone 7, which is a bolt on top of the engine block directly above the transmission just towards the passenger side. There is another lighter gauge ground wire already attached to the block at Ground 106.

The problem is I can't get at this bolt to use it. I finally took the right front wheel off and the right front inner fender liner and I can just barely see 106. If I get up on top of the engine on my knees I can just barely get my left hand around the trans dipstick tube and everything else in that area to touch the bolt at 106.

I can probably get a 1/4 wobbly extension to go straight down from the top between the firewall and the block to get the bolt out. But it would be a long-shot to try and manipulate the new cable onto the bolt with the existing cable and get that bolt restarted in the hole using only a couple of fingers on the left hand. There is just not enough room back there between the firewall the and the engine for me to get my big hand in there.

I've been using all manner of lighted inspection mirrors, inspection camera, from below, from above etc to find a decent ground point and I'm not coming up with many options. The aux battery negative cable is too short to reach to the other side of the block where the start battery negative cable is attached to the block, and even if it was I'm not sure I could access that bolt either because it is buried up in and above the engine mount tight against the block.

For now I put the aux negative cable on a stud on the firewall on the drivers side which has a ground strap that is connected to the engine block on the drivers side similar to 106 on the passenger side. This is not factory and it may not be good 'electrical practice' but I needed to get the truck back in service until I have another window to work on this project again.

The only other possibility I could see to use the factory aux negative cable and may be better than the firewall ground is this bolt/stud holding the bell housing to the block. The bell-housing is aluminum of course, but the bolt is steel and assuming it is a mounting bolt it would be grounded to the block via this bolt would it not? This stud appears to be of the right diameter, has enough threads on it, close enough for the aux battery neg cable to reach, and is somewhat accessible for installation.

Would this be a better bet than the firewall ground stud or is it six of one half dozen of the other?

Thanks

asilverblazer · June 17, 2010

or is it six of one half dozen of the other?

I'd say yes.

herm0016 · June 17, 2010

i am gathering the parts to do this mod to my truck, i think that the current solution is quite good as that ground strap goes to where you were going to mount it. The bolt on the bell housing would also work fine. I may change the fitting on the end of the wire to be the right size though. Thanks for posting.

nickvrebel · June 17, 2010

go to the block. you can take off a transmission bell housing to engine bolt and use that if needed, 15mm and it can be accessed with a box end wrench.

On the newer trucks with the main battery now on the passenger side they used one of the empty accessory bolt holes on the front of the block.(or is it on the head? can't remember, either will do). You may have to get an extra bolt from the hardware store but that wouldn't be a big deal. Either way, ground to the motor, not sheet metal if at all possible.

ETA:

these motors are EXTREMELY picky about their grounding, causes headaches when doing motor swaps sometimes.

SavageNFS · June 17, 2010

Is this the bolt you are referring to? I realize it is a different year truck, not sure if your truck looks different.

Closer look...passenger side, near oil fill

That is the bolt that I used to tap the block and I didn't have any issues. I did use a 2' step ladder, but other than that, no issues reaching it. It is not recommended (at least in the car audio world) to ground the batteries at different locations. If the primary is grounded to the block, the aux battery should be grounded to the block as well.

Wayne02 · June 17, 2010

Thanks for the replies. Further investigation of this particular bell-housing bolt reveals some possible challenges with heat from the exhaust manifold as the cable is routed to the top where the battery is. I thought they made some sort of heat shield tape for these type of applications but the napa people say they know of no such thing.

SavageNFS,

My truck has a big egr tower thingy in that location, but maybe I can pull one of the mounting bolts and put the cable underneath the head of one of those bolts.

Is it ok practice to ground to the head? Steel head, steel bolts, same ground path, yes?

Another idea that has come up is to remove the eyelet terminal on the end of the factory aux battery negative cable and replace it with a fork terminal or even just snip the end of the eyelet terminal off, effectively making it a fork terminal. Then I 'might' be able to slide the fork terminal under the ground bolt in the near inaccessible location #106 without actually removing the bolt from the block (just loosening it). I realize a fork terminal is not as good as an eyelet terminal, but...

fraiolib · June 18, 2010

how does the camper only draw from the aux battery?

SavageNFS · June 18, 2010

Is it ok practice to ground to the head? Steel head, steel bolts, same ground path, yes?

Another idea that has come up is to remove the eyelet terminal on the end of the factory aux battery negative cable and replace it with a fork terminal or even just snip the end of the eyelet terminal off, effectively making it a fork terminal. Then I 'might' be able to slide the fork terminal under the ground bolt in the near inaccessible location #106 without actually removing the bolt from the block (just loosening it). I realize a fork terminal is not as good as an eyelet terminal, but...

Yes (to grounding to the head is ok) and don't use a fork to split. Use a designed fitting if you go that route. I use JL Audio stuff. Something like this:

You can and should use something cheaper (Stinger makes some decent stuff). Just remember that if you are going to take two 4/0 wires and join into one (via a "Y" or fork), then up the wire going out. Two 4/0 wires going in mean 2/0 wire coming out (minimum). You'd be better off grounding to the head...seriously.