grounding question re: the neg battery cable

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kenicb

kenicb

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Hey there, I need help understanding how the ground from the neg battery cable affects the ignition system

-why does the neg battery cable have 2 grounds?: One to the main block and one to the chasis of the car

-if you only used a single ground to the block (like on my tractor), would this affect
the ignition system and if so why?

Trying to be smarter than the machine that's trying to beat me

Thanks so much. God bless

Keni
 
I'm just guessing here, but probably because of the rubber motor mounts which isolate the two?
 
Yup, motor and trans are mounted by rubber. Should be a ground from the back of the engine to the firewall too.
 
OneOfMany said:
... rubber motor mounts?...
Click to expand...

Pretty much yup. Typical older factory setups had the main battery cable hooked to the block, and a jumper from the battery to the body, and sometimes a jumper from the block to the frame/ body. Both these jumpers were typically no10 or so wire

VERY important that the body/ frame and block be well tied together, especially nowadays with all this electronics. Electrical "noise" can cause all sorts of problems in all sorts of equipment, ignitions, computers, etc, as well as the age-old problem of the regulator putting out too much voltage because it does not properly "see" the battery
 
"VERY important that the body/ frame and block be well tied together, especially nowadays with all this electronics. Electrical "noise" can cause all sorts of problems in all sorts of equipment, ignitions, computers, etc, as well as the age-old problem of the regulator putting out too much voltage because it does not properly "see" the battery"

2 more questions:
-from what you are telling me if the smaller no 10 gauge ground from the battery to the frame is not there, this will affect the voltage regulator. If the voltage regulator puts out too much voltage how does that effect the coil?

my engine does not have the third ground from the block to the frame. How does this connection help?

thanks so much
 
I said no10 only because this is what the older factory stuff used. I should have said that "bigger the better."

All loads in the car except ignition are grounded to the body/ frame, not the block. This means a good connection from the block to frame is important.

The regulator only can control "what it sees." One of my favorite posts is to have guys check their regulator wiring BEFORE they replace a regulator that may not be bad

The regulator is bolted to the body, so if it's not the same voltage as the battery negative, the battery will be running "too high." Same deal on the voltage TO the regulator, from the key, ---here's the deal

The ground path from the battery negative post---through the cable to the block--through the extra ground from block to body--to the regulator mount.

All this can add up to "voltage drop," a tenth of a volt here, a hundredth or two there. When all's done, the regulator may be "above ground" from the battery negative post. The charging voltage INCREASES at the battery by this amount of drop

The SAME is true of the drop on the positive side. Here, the path is from the battery--through the cable--to the big stud on the starter relay--fuse link--through the bulkhead connector--through the ammeter--to the connector at the igntion switch,--THROUGH the switch contacts, --BACK out the switch connector, --BACK through the bulkhead connector, and finally to the "dark blue" ignition run wire in the engine bay, which feeds the ignition, the alternator field on '70--later cars, the REGULATOR ign terminal, and the electric choke if used.

SO THIS PATH has a lot of places to lose voltage, including the bulkhead connector, (twice) the ignition switch connector, (twice) the switch itself, and any other poor connections along the way.

So if this voltage is say, "trying to be" 1/2 or more volt LOW by the time it gets to the regulator, the regulator just jacks it up UNTIL it's at the regulator setpoint, say, 14.2 AT THE IGN TERMINAL. But the CHARGING VOLTAGE at the battery IS NOT 14.2, because of the voltage drop in the harness. You ADD the setpoint (example 14.2) to the voltage drop, say 1/2 volt, and now the charging voltage at the battery is now up to 14.7, and I didn't include the drop in the ground side, which will add whatever drop is in the ground circuit.
 
wow. i think my head exploded when i read it the first time. :scratch: way over my head. But Ive read that three times and now Im starting to understand it. thank you so much for taking the time to explain it with such detail.

I took what you taught me, and walked out to the garage with a better attitude. i learned from a practical standpoint by checking each connection with a volt reader. I started seeing how a little loss here and a little loss there, added up to a significant drop in spark at the coil. once I cleaned up all the connections, and installed all three grounding wires, my coil spark was full on. The engine jumps to life almost instantly now, when the key is turned.

thanks for the help

God bless

keni
 
Glad you made some headway. Just about anything is suspect in these old cars nowadays, the connectors, switches, and especially the bulkhead connector

These were not exactly wired with oversized wire to start with. Let's say you are towing a trailer --which I did, when I had my old '70RR. Adding another set of tail/ turn lamps to the "already small" tail lamp harness brings a noticable drop in lamp brightness back at the trailer.
 
Basic automotive wiring theory 101. Great job guys. I am breaking myself of an old habit of using a test light and using a multimeter. I fried a battery and blew out most of the light bulbs in my car a few years back because I didn't have a proper ground on a new electronic voltage regulator. The alternator was charging at 16 1/2 volts plus. toolmanmike
 
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