backrodebob
Member
thoughts on where to ground battery? engine or frame?
battery ground
- Thread starter backrodebob
- Start date
dmsfrr
Well-known member
What vehicle are you working on? Is it 6 volt or 12?
A battery ground cable is generally more effective when connected to the engine, so it's a shorter & higher current capacity route with fewer connections to 'battery ground' for the starter... which is usually the highest current draw part on the car.
But it can depend on the vehicle if you're wanting to stay 'as original'.
Newer vehicles may have the battery ground cable to the body, with another ground wire from the body to engine. Especially if they have a large number of power consuming accessories.
Some electrical items may have their own dedicated ground wire back to the battery terminal.
Most electrical items are mounted/grounded to the body or engine of the vehicle, not to the frame.
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A battery ground cable is generally more effective when connected to the engine, so it's a shorter & higher current capacity route with fewer connections to 'battery ground' for the starter... which is usually the highest current draw part on the car.
But it can depend on the vehicle if you're wanting to stay 'as original'.
Newer vehicles may have the battery ground cable to the body, with another ground wire from the body to engine. Especially if they have a large number of power consuming accessories.
Some electrical items may have their own dedicated ground wire back to the battery terminal.
Most electrical items are mounted/grounded to the body or engine of the vehicle, not to the frame.
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evintho
Senior Member
On my last 3 projects I grounded the batt to the frame, using the frame as a ground plane. On my current '54 project I used a short 1/0 ga batt cable to a 3/8" stud welded to the frame. Accessories are wired to a ground bar which is grounded to the brake pedal bracket up under the dash. I run a short 4ga ground cable from the firewall to another 3/8" stud welded to the frame. I also run two 4ga ground cables from each side of the engine to 3/8" studs welded the the frame. That pretty much covers any ground issues. I did the same thing to my '27 roadster and my last '89 Mustang. Never had a ground issue with either car.
backrodebob
Member
I have a weak spark I can’t figure out? so , I’m at the point of fishing for ideas!
backrodebob
Member
8ba 12volt mallory Replace wires, spark plugs, coil compression test and went through and cleaned all grounds. what am I missing?
Is the Mallory distributor electronic or points? An electronic would usually require a coil without a ballast resistor. A point system needs a ballast resistor and if you have points, make sure your running voltage to the coil is at least 9.5-10 volts and if you don't have a ballast bypass when cranking the engine, then connect it in at your solenoid.
As far as grounding, I've done like the manufacturers do, the cable from the battery directly to the engine and a cable from the engine to the frame
As far as grounding, I've done like the manufacturers do, the cable from the battery directly to the engine and a cable from the engine to the frame
Flathead Fever
Well-known member
You always want to run the ground cable from the battery directly to a starter mounting bolt since it requires the most current. That way you don't have any voltage drop. Then because the engine is mounted with rubber engine mounts the body needs another ground. that can be from the engine to the firewall. The more grounds the better, always put star washers under the cable ends so they bite into the metal for a good connection and grind away any paint.
Fun story. In the 1970s, when I was 16, I was building a fake '65 Shellby GT-350. The '65s had the battery in the trunk. So, I mounted it back there and ran a heavy positive welding cable from the battery in the trunk to the starter solenoid. I just ran the ground cable from the battery to the trunk floor. When I went to start it, it cranked but I could see smoke coming from the engine compartment I got out and the manual choke cable was smoking. I didn't make the connection and dumb me grabbed it and it burned the crap out of me. it left the spiral marks from the cable housing on my hand like hot dog barbecue grill marks. It turns out the only ground that started motor could find was that metal choke cable. I didn't reaize that the engine is mounted in rubber, the trans has a rubber mount, the rearend has rubber bushings on the springs. I would have thought in all of that stuff there would have been decent ground. Nope, just a choke cable. I ran a heavy ground cable from the battery in the truck to the starter mounting bolt, A ground from the battery to the trunk floor and another ground like the factory had from the intake to the firewall.
Fun story. In the 1970s, when I was 16, I was building a fake '65 Shellby GT-350. The '65s had the battery in the trunk. So, I mounted it back there and ran a heavy positive welding cable from the battery in the trunk to the starter solenoid. I just ran the ground cable from the battery to the trunk floor. When I went to start it, it cranked but I could see smoke coming from the engine compartment I got out and the manual choke cable was smoking. I didn't make the connection and dumb me grabbed it and it burned the crap out of me. it left the spiral marks from the cable housing on my hand like hot dog barbecue grill marks. It turns out the only ground that started motor could find was that metal choke cable. I didn't reaize that the engine is mounted in rubber, the trans has a rubber mount, the rearend has rubber bushings on the springs. I would have thought in all of that stuff there would have been decent ground. Nope, just a choke cable. I ran a heavy ground cable from the battery in the truck to the starter mounting bolt, A ground from the battery to the trunk floor and another ground like the factory had from the intake to the firewall.
Flathead Fever
Well-known member
Everybody needs a digital voltmeter. The very first thing to check is the available voltage to the coil with the key on and points open if it uses points. If the points are closed it will read zero. Then like others have said you need to know if your coil has an internal resister or requires and external one. You don't want them both or it will cutdown your voltage too much and you will have a weak spark. You can try another condenser and those are rated to match the coil. You want to use the condenser with the same capacitance that was originally used with whichever coil you are using. They are a matched set. Make sure you don't have the polarity on the coil reversed. Make sure it's a coil made for positive or negative ground and 12V or 6V depending on what you have. Check the coil wire spark compared to a plug wire spark.
If its electronic ignition you want to use a special "test spark plug". All the auto parts stores have them. What can happen if you do not use the test plug is when you hold just the spark plug wire away from a ground, the coil will try to build up whatever voltage it takes to jump the gap. If you're holding it too far for the spark to jump the coil will build up a large voltage that will look for another path to ground and it can backtrack trough the electronic ignition module and damage it. I was master mechanic for 30-years and the manuals warned against checking for spark on electronic ignitions without using a test plug. It can burn a microscopic hole in a transistor that over time cane fail. It won't do it right away. A couple years later your ignition module could fail, and you won't realize it was from when you tested for spark a long time ago. Better safe than sorry.
If its electronic ignition you want to use a special "test spark plug". All the auto parts stores have them. What can happen if you do not use the test plug is when you hold just the spark plug wire away from a ground, the coil will try to build up whatever voltage it takes to jump the gap. If you're holding it too far for the spark to jump the coil will build up a large voltage that will look for another path to ground and it can backtrack trough the electronic ignition module and damage it. I was master mechanic for 30-years and the manuals warned against checking for spark on electronic ignitions without using a test plug. It can burn a microscopic hole in a transistor that over time cane fail. It won't do it right away. A couple years later your ignition module could fail, and you won't realize it was from when you tested for spark a long time ago. Better safe than sorry.
dmsfrr
Well-known member
If the distributor has points, they need to have a good ground wire/path to the distributor housing, which is grounded to the engine block.
Also check the polarity of the ignition coil. It should match the polarity of the rest of the electrical system.
In a negative ground vehicle the negative/dist terminal on the coil goes to the points.
On a positive ground vehicle the positive/bat terminal of the coil connects to the points.
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Also check the polarity of the ignition coil. It should match the polarity of the rest of the electrical system.
In a negative ground vehicle the negative/dist terminal on the coil goes to the points.
On a positive ground vehicle the positive/bat terminal of the coil connects to the points.
https://mgaguru.com/mgtech/ignition/ig104.htm
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Daves55Sedan
Well-known member
As an example, here is what I did on '55 Ford, 6-volt, with Y-block engine:
Main (+) ground post from battery to engine dipstick mounting bracket (that is the factory setup), but I added a beefy 7-strand #2 awg insulated cable from that same dipstick bracket to the top starter mounting bolt.
There is a factory #8 awg yellow ground wire that bolts to the front engine steady-rest and down to the backside of the front frame crossmember for grounding of the car frame.
There is also a factory #8 awg yellow ground wire that runs from the rear left head of the engine to a nearby firewall lag screw for body ground.
If these all have good tight, clean and non-corroded connections, you should have good ground to engine, frame and body.
Main (+) ground post from battery to engine dipstick mounting bracket (that is the factory setup), but I added a beefy 7-strand #2 awg insulated cable from that same dipstick bracket to the top starter mounting bolt.
There is a factory #8 awg yellow ground wire that bolts to the front engine steady-rest and down to the backside of the front frame crossmember for grounding of the car frame.
There is also a factory #8 awg yellow ground wire that runs from the rear left head of the engine to a nearby firewall lag screw for body ground.
If these all have good tight, clean and non-corroded connections, you should have good ground to engine, frame and body.