I looked everywhere in my FSM, couldn't find any diagrams for chassis grounds. Figured I clean them up . Went for ride last nite with top down, stopped an ate, on the way home Service engine light came on , pulled a code 36....MAF sensor burn off. Pulled them from firewall an cleaned the electrical connectors, an checked wiring. Before I go any farther replacing parts, I want to check the grounds. Thanks PS; Makin small talk with waitress, told her I was out on shake down run in the 86 vert, she went out to look at it, asked "oh a 2 seater" Couldn't resist, told her there were 2 seats under rear deck lid....

 

"Agent86" posted these locations quite some time ago and I do believe there should be maybe 5 - 6 pages of grounds in the FSM. I don't have an '86 FSM but there is in most all of them.

G101-near RH side of battery, on frame.
G104-on block, above oil filter
G115-on frame, behind LH park/turn lamp
G116-on frame, behind RH park/turn lamp
G117-LH side of engine compartment, on front cross member
G125-behind RH kick panel
G201-behind I/P, near LH side of steering column
G320-LH B pillar
G400-on frame, above LH rear wheel
G401-base of RH B pillar

This list looks pretty complete.

 

Nawwwww

tell her there's a mattress back there........


Back to the grounds...

There are grounds placed near the device they service. That's EVERYWHERE.

There are really only a few that you are concerned with. There is a cable from the battery to the frame that is of minor consequence. There is a small strap from frame to block...again, little consequence.

What you NEED to be concerned with are the several (5) that drop out of the harness trunk line on the firewall behind the booster, down to the block, to a bolt somewhere over the OIL FILTER,. these are NOT easy to see. There are NOT easy to reach from above or below.
they are however, CRITICAL because these are all the grounds for the engine EFI, the ECM and the cabin controls.

Find them, clean and reattach.
The electrical system is like the blood vessels in your body....they MUST stay clean and allow good flow otherwise things start to go wrong...quickly. The elec system on the C4 is all controlled by GROUNDS...NOT hot wires. MOST of the things on the car have the hot wire, HOT all the time. Its the GROUND that is used to break/connect to manage and control everything from the a/c to the engine sensors and servos.

Adding a ground cable from battery to frame/block is a good idea.

Taking off and cleaning the HOT wires on the jumper pole behind the battery is a GREAT idea. These are the HOT source wires for EVERYTHING. Again, these are HOT all the time. Orange is always ON, Red is Key ON. Point is, they are always ON, so the connections MUST be clean and tight. Resistance is the secret to this system. Its used to gauge and monitor things, so when the resistance changes due to poor dirty contacts, the operation of something changes as well. Often its the engine. Mystery misfiring, poor performance, fuel economy etc....often traced back to dirty wire harness.
BTW...
you also have a handful of FUSIBLE LINKS inline for these 'hotwires' to the jumper pole, because many of these circuits bypass the fuse block/panel. The fusible links can be found UNDER the battery box. NOT a problem until something goes dark for no apparent reason...that's actually rare. Just know where these things are just in case....

if you get the several black wires cleaned over the oil filter and make sure the battery cables are tight, and clean the HOT wires on the jumper pole, that's 99% of the maint on the grounds. The others are scattered all over and usually are not a problem until something specific fails like the antenna or the wiper washer pump...then you track 'em down after some trouble shooting via the FSM electrical book.
Good luck !

OMT
the black wires that we want to find over the filter, come from the main harness. The splice in there is very CHEESEY and fragile. Do not tug on the wires from the firewall harness section....they CAN easily be pulled out of the simple crimp that holds them on the harness black wire. Its as cheap as it gets...IF you can pull the plastic conduit back enough to look and see, you will see what I'm talkin 'bout. Look for cracked insulation on wires as well. This harness is fragile, never was quality wire in these things. Its 30 yrs old now and the life expectancy of the wire is just about there.......be gentle !

 

Thanks for info, I'll track em down an get them cleaned up, being very careful with the ones on block over oil filter...Thanks again Ziggy

 

Found wire pulled out of end, an a lot of crud, At ground to block above filter..Boy they did go cheap there...Had to get "lil" woman in to strip an re solder wires...She's a keeper...lol

 

Any hints on how to get to the G104 ground on my '88? I found the wires but cannot see the bolt that attaches them to the block and am trying to be careful with the fragile wires. I even took some pics from different angles and the wire connections do not look like the sketches I have seen. I do have a FSM which mentions the locations of the ground. I am trying to check this because after replacing the head gaskets, etc., my speedometer doesn't work. I thought it would be good to clean all of my grounds. The speedo did work before the head gasket change. Other gauges and DIS all work. Thanks for any help.

 

Here is G104 on my 86

 

My '88 version of G104 area. Is the G104 bolt just barely visitble near the upper right in the crook of the corrugated wire set? Looks different from the '86 pic and different from what my '88 FSM shows. Not sure if it might have been changed at some point before I got it.

 

I pulled the battery an battery tray out, needed to get to ground G101 under battery tray. Mine was corroded from battery acid, bolt was stripped. Got three 12" 3/8 drive extentions , first one holding socket was a wobble tip. Got bolt loose for ground G104 above filter, I had better luck jacking up left side of car an removing bolt from under car. It's tight...you might be able to get your hand into loosing bolt from above, mine didn't fit. wife had to help get back together, as her hands are smaller.....Ziggy

 

The REAL question here is.........


how'd you get that pic with THAT much room around the area ???????


That had to be done with a cable-scope or something similar. I can't even get my phone in to get an angle like that and come away with a good photo !




EDIT:

duhhhhhhhhhhh


just saw the exhaust port.... !

 

That was my problem as well. I took about 8 pics from above and below by just blindly taking shots since I could not come close to seeing it. The one with the AC oil filter was by far the best but still does not really show the G104 bolt that I was trying to see. My '88 just seems to have a jumbled bunch of wires, not the neat connection of the '86.

 

Was going to say, looks like the whole front end is off. I can just see mine looking over battery tray...LOL ziggy