How many ground strap connections do I need, anyway?

454GrandPrix

454GrandPrix

Master Mechanic
Jul 27, 2016
428
93
Lehi, Utah
My BBC-swapped 1980 Grand Prix has only two ground connections (not counting the interior). One is the negative battery cable connected to the passenger cylinder head (with no smaller wire going to the body), and the second is a small flat braided ground strap connecting the firewall to the intake manifold. That's it.

Problem: my TCI EZ-TCU controller occasionally loses the output speed signal from my 4L80E. When this happens, the controller assumes I am not moving... so it puts the transmission in 1st gear and it will not upshift. Fortunately, moving the shifter to '2' forces the transmission into 2nd gear, so if the controller gives up I can at least have two out of four gears and limp my way along. The only way to correct the problem is to completely shut down the car, wait for the electronics to 'go to sleep,' and then re-start it.

At first, I thought this was an obviously bad speed sensor so I replaced it with a new Delco one. No change. Now I'm wondering: what if there is a weak ground that sometimes interrupts the sensor's output signal? It is a running joke with some of my car friends that any electrical problem is always the fault of insufficient ground straps. Could that possibly be my problem?

I'll stop by O'Reilly and buy an upgraded negative battery cable which also has the integrated small line to connect to the body. (I've actually wanted to do this for a while.) That will give me one more ground connection. But could/should I somehow also add one between the transmission housing and... something? Maybe I can connect one of the transmission bell housing bolts to the firewall, for example?

Thoughts?
 
Gonzo1970

Gonzo1970

G-Body Guru
Supporting Member
Sep 30, 2018
840
93
Two.

Battery Negative to Body.
Block to Firewall.


-Gonz
 
Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
7,383
113
Queens, NY
My buddy has a '55 Chevy hot rod. He had lighting issues and kept blowing the $100 infra-red MSD module. I took a look and the only ground was by accident through his clutch linkage. We ran braided mesh grounds from the engine to the frame, from the engine to the body, from the frame to the body, and a dedicated ground from the battery to the MSD distributor. End of problems. You can't have too many grounds.
 
melloelky

melloelky

Royal Smart Person
Oct 22, 2017
2,360
113
mass
The more the better. Electricity/Contunity's like water it follows the path of least resistance.ive got one frame to body,motor to frame,another frame to body in the rear and i made the one from the negative cable to fender larger. grounds are a cheap and worthwhile upgrade,i made mine from Universal battery cables with an eyelet one each end.dont forget the star washers they too make the difference.
 
fleming442

fleming442

Rocket Powered Basset Hound
Dec 26, 2013
11,033
113
Remember, kids: electrons flow from negative to positive. Mo grounds= mo betta.
 
Texas82GP

Texas82GP

Geezer
Supporting Member
Apr 3, 2015
5,857
113
Spring, Texas
My BBC-swapped 1980 Grand Prix has only two ground connections (not counting the interior). One is the negative battery cable connected to the passenger cylinder head (with no smaller wire going to the body), and the second is a small flat braided ground strap connecting the firewall to the intake manifold. That's it.

Problem: my TCI EZ-TCU controller occasionally loses the output speed signal from my 4L80E. When this happens, the controller assumes I am not moving... so it puts the transmission in 1st gear and it will not upshift. Fortunately, moving the shifter to '2' forces the transmission into 2nd gear, so if the controller gives up I can at least have two out of four gears and limp my way along. The only way to correct the problem is to completely shut down the car, wait for the electronics to 'go to sleep,' and then re-start it.

At first, I thought this was an obviously bad speed sensor so I replaced it with a new Delco one. No change. Now I'm wondering: what if there is a weak ground that sometimes interrupts the sensor's output signal? It is a running joke with some of my car friends that any electrical problem is always the fault of insufficient ground straps. Could that possibly be my problem?

I'll stop by O'Reilly and buy an upgraded negative battery cable which also has the integrated small line to connect to the body. (I've actually wanted to do this for a while.) That will give me one more ground connection. But could/should I somehow also add one between the transmission housing and... something? Maybe I can connect one of the transmission bell housing bolts to the firewall, for example?

Thoughts?
My 82 GP was a diesel car originally. It had a ground cable that ran from the lower firewall, near the body mount on the driver's side, up to the engine. It was battery cable size and was insulated like a battery cable. If I remember right, it was bolted to the back of the head on the driver's side on the 400 SBC that had been transplanted in the car. I'm going to put it back like that. You can see it dangling by the driver's side frame rail in the pic below. Glad to see you're still around and enjoying your car. I have to get back on mine!
P1010004.JPG
 

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