When runnning grounds for EFI, you can not over do it..

You can ground the battery to the unibody if you weld in a proper terminal.  That will give you what you need for starting the car, but you also need to ground the EEC (or aftermarket processor) directly to the battery, so run a dedicated decently sized ground from the battery post to the EFI.

John

Here's what I've done with a couple of harnesses and had no problems so far.  Hegos, 60/40, ignition shield, about all of the EFI grounds, all come together and ground to a 3/8 stud at the back of the right cyl head.  Also from that stud I have a fairly heavy ground strap attached to the firewall.  All relay grounds are put down to the left fender apron where my home-brew PDB is mounted.  I think I pick up some other ground there also.  The battery neg cable goes directly to the engine block and attaches with a 3/8 bolt.  I also have a 12Ga hot and ground running to the FP at the fuel tank.  The FP ground comes forward and I think it goes down with the  other grounds near the PDB.

All ground surfaces were cleaned of any paint/corosion before making them up.  Then I touched up the engine bay paint as needed with RO 7777.

I've never had a problem or any indication of high resistance or poor grounding either with the enginge mgt system or any lighting.  Main thing I've found over the years is that you bond every part of  the car together:  Body, frame, engine/trans, battery, and in some cases, the running light socket bases.  And always ground the neg cable to the engine block/trans for minimun resistance.  Rear battery applications need to take care with this and do it right...ask Corky how we know about that.

Ford distributes the grounds all over the car but I don't know if that has to do with convienence or some other reason but I'm betting convienence ($$$$).  As long as everythig has a solid, clean path to the neg batt post you'll be okay.

BB

Thanks, and you peaked my interest, what happened to Corky with his battery relocate?

Bullet Bob wrote:

KStang wrote:

Thanks, and you peaked my interest, what happened to Corky with his battery relocate?

Just run a heavy ground cable all the way forward to the engine or trans.  DO NOT rely on a Neg cable connection at the rear frame rail or body.

BB

Yup!

JamesW wrote:

I have a trunk battery with EFI - 
Negative cable straight to the rear frame rail
Welded subframes
Large cable from engine block to front frame rail
Cable from block to firewall

Never had any issues

Agree: the unibody can carry as much current as any cable you can fit in the car IMO.   But I would still suggest a decent sized (14 ga) ground wire from the battery back to the processor.

John