Ground Bus

[Bitsyncmaster]

I think it is worth mentioning that even though a car has a ground bus installed, it is still important to maintain the original ground from the negative battery terminal to the trailing arm bracket bolt. When you have a ground bus, you have a parallel ground circuit assuming that the bus is attached to the radiator bracket. One path is the bus, the other path is via the frame to the trailing arm ground.

If the ground connection is lost at the TA bracket (I've had that happen on a tight metal on metal connection probably due to galvanic action), then the starter and other engine related currents will follow the frame to the radiator bracket, to the ground bus to the battery. The starter current is the only significant load, I presume the 4gauge bus will carry it but it is a long run of 4gauge.

To the extent that there is resistance (corrosion or wire length) on the paths, the two paths share the current load per Ohm's law. In other words, the ground bus carries a portion of the fuel pump (selected purely as an example) current as does the frame (again assuming that the ground bus is attached to the radiator bracket & the negative battery terminal). The extent to which each carries some load is a function of the path resistance. Bad junctions such as potentially at the TA bracket bolt increase resistance and alter the amount of current on each path.

CONCLUSION: even with a heavy duty ground bus, maintain or improve the ground connections at the TA bracket, engine and or transmission.

Next week I'm off to the scrap yard for another negative battery cable as a jumper from the TA bracket to the Transmission... and I may even consider a continuous wire or soldered connection from the battery negative to the TA bracket to the transmission just to avoid the possibility of corrosion at any junctions.

Nick

Agree. I need to do a measurement of the resistance of the frame someday. Yes steel is a poor conductor compared to copper but with all that area in the frame it may not be aiding you much to install a copper ground buss. The buss does make less voltage drops if you rewire your existing circuits to it. It makes it easier than using the frame as the buss.

All I need to do is measure the voltage drop from the front frame terminal to the rear frame terminal (TAB) with the fans running. Then knowing the current draw on the fans I can compute the resistance of the frame. Then I can compute the resistance of a #4 AWG copper wire and see what that in parallel will buy you.

[content22207]

I think it is worth mentioning that even though a car has a ground bus installed, it is still important to maintain the original ground from the negative battery terminal to the trailing arm bracket bolt.

Not if the bus has its own connection to the battery.

I could disconnect all original frame ground points and my car would operate exactly the same. Every one of them has been rendered redundant.

My new battery to bus connection is far superior to the original trailing arm ground because:
- Terminals are soldered on both ends
- It is located inside the car (weather tight)

Bill Robertson
#5939

[nkemp]

I like your ground bus and have added it since my last dead D experience this week. I have planned on doing so for a while and wish I had done it sooner.

If I understand the bus in your car:
- You have a new ground from the bus to the engine
- The bus also connects to the frame at the radiator bracket

If correct then yes you can disconnect the TA ground. Now one needs to maintain the grounds at the engine and potentially the front bracket (both subject to the weather). The ground at the engine from the bulkhead ground is what caused my D to get the nice guy with the flatbed to give me a not-free ride home the other day (lost the fuel pump ground circuit).

The problem we face when grounding to the engine or frame is galvanic corrosion. Combinations of aluminum, copper, zinc, steel, water, electrical flow and oxygen results in "activity". (As I recall, aluminum & copper is especially bad)

Your ground bus is superior to the original and the community is better off with this knowledge. I still think we must remember that the connection points at the frame &/or engine are not trouble free. We need to maintain those points or develop a better method. I prefer the latter.

Nick Kemp

[content22207]

I'll be damnded if I am going to lay on the ground and mess with the original frame to battery ground. Same with the original braided strap. If they work, great. If they fail, I'll never know it.

My engine is actually grounded three times:
- Original braided strap
- 4 gauge cable on the other motor mount (installed before my bus):
MotorMount.jpg
- Ground bus
GroundBusEngine.jpg

I have no intention of even thinking about my DeLorean grounds through the next decade or two of ownership.

Bill Robertson
#5939

[1batt4u]

I bought the 2 battery cables from John Hervey. I know one replaces the one on the chassis, right next to the coil. Where does the other wire go?

[stevedmc]

I bought the 2 battery cables from John Hervey. I know one replaces the one on the chassis, right next to the coil. Where does the other wire go?

It is basically an extension that runs to the transmission.

[1batt4u]

Is this it??

[Ashyukun]

Is this it??

Nope- that's the stock frame-to-engine block ground, though the second run of wire in Hervey's kit does somewhat duplicate its functionality by hooking up the ground to the transmission, which is of course bolted fairly securely (or should be, at least...) to the engine. One end of mine is hooked up to TAB bushing connection along with the line from the battery, and the other end I found a convenient bolt on the transmission to pull, clean off, and bolt the ground to it.

[aludden]

So, how did you traverse the fiberglass?
. Relay box to bulkhead connector
. ECU compatment to engine
. Dash to radiator bracket
. Battery to Relay box

Did you drill holes?
Thanks!
Alex

[Farrar]

Bill's not here so I will try to answer that question for Alex.

I believe most of the people who have done ground bus runs have had to drill holes in the fiberglass, because the wire they were using was so thick it couldn't be threaded through existing grommets. Also, I think Bill's version of a ground bus also grounds the metal bracket behind the passenger seat (similar to the grounding of the bracket behind the driver's seat). Of course, you can go about it in a different fashion. I think the idea is sound, but 4 AWG wire is a bit overkill in my opinion.

I hope that helps!

Farrar