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garretthes

Battery ground wire question

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Previous owner seems to have screwed up the starter/Battery wiring. The - cable from the battery is grounded to the chassis but there is another place for it to ground but I can't see where. The cable has 2 lugs.

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The - cable should ground on the block.Usually up front near the fuel pump.But i relocat them to as close to the starter as i can.And having the cable also grounde to the chassis is a good idea.

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On my '71 240Z the cable has two leads, one heavy and one small. The small one connects to a threaded hole on the firewall near the battery. The heavy lead connects to the upper of the two starter mounting bolts.

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On my '71 240Z the cable has two leads, one heavy and one small. The small one connects to a threaded hole on the firewall near the battery. The heavy lead connects to the upper of the two starter mounting bolts.

Same as my'72.

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Same as Arne, Gary and Kim.

When you connect to the firewall, try to sand down to bare metal and throw a little dielectric grease under the ring terminal when you bolt it on. Improves the connection and helps prevent future corrosion. Bad electrical ground can really drive you crazy trying to track down.

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If you pefer a better looking Battery top, Run an 8 gauge wire from the same bolt as your ground wire mounting point, and connect the other end to the same point that your Engine harness is grounded. It's kinda like bolting your engine harness to the battery, but you get a cleaner look from the tranny bolt to the frame rail and along the harness to an existing ground bolt.

And just like Bart said, Fresh Grounded metal, dielectric grease and BOLT it down good an tight. then place a little more grease on the outer surface to protect it any further.

What most folks don't realize is that when you bolt your battery ground to the tranny, the engine is mounted to the frame with Rubber!!! The only real ground from the battery is the little wire from the battery clamp to the firewall, AND, that alternator ground to the engine harness and body at that one little point.

Dave

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I have a good chassis ground but there is no engine ground. The cable I have will not reach so I'm headed to the parts store for a jumper.

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I'm planning on bolting it to the top starter bolt. That sound good? I will run one end to the chassis ground or should I take it to the clamp?

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Just run a good 4 gauge ground wire from the Neg post on the battery to the top starter bolt. And make sure it has a good lead wire on it to be bolted to the firewall near the battery. THEN run another wire (8 gauge) from the top starter bolt (bolted to the tranny) over to the ground wires on the engine harness.

That should do it.

Dave

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When I replaced my battery this summer I bought a dual post battery. I used one #4 AWG cable to connect the top post of the negative side to the engine block, and a second #4 AWG cable to connect the side post of the negative side to a ground bar that I mounted on the firewall.

(I have several relay circuits that connect to ground so I needed the space.)

The ground bar was only about $3 at Lowes. It is rate to accept a #4 wire, but the opening is sized for a solid wire so a stranded #4 has to be trimmed slightly.

Just throwing out ideas.

post-3035-14150812050051_thumb.jpg

Edited by Walter Moore
Corrected my grammer.

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OK guys, I think we are good to go. Followed your advice..mostly. Ran the existing 2 gauge cable to the top starter bolt and also ran a 4 gauge from the top starter bolt to the chassis where the cable was connected before. Then I ran a 10 gauge wire from the neg terminal across to the engine wiring harness ground. Now the wires are not heating up during starting.

Currently the car is under plastic with a bug bomb inside and under the car. It will sit there until Thursday evening when I will add some gas and try to get it started.

Thanks and I will update Thursday

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You might consider going through the fuel system, injectors back to tank, filters, to remove possibilities of junk / rust particles and the over 2 year old fuel that is left in the tank. Start fresh.

Bonzi Lon

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Update: Tried to crank it again today with gas. No luck, more wires smoking. Not nearly as bad as before but still there even with the ignition on the wires smoke.

Dang! Is there another engine ground other than the one on top of the engine with the harness?

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Update: Tried to crank it again today with gas. No luck, more wires smoking. Not nearly as bad as before but still there even with the ignition on the wires smoke.

Dang! Is there another engine ground other than the one on top of the engine with the harness?

If you have wires smoking with the ignition on, it looks like you already have too many grounds. Find the "extra" ground (the short) and the proper ones might work correctly.

You may have already created new shorts from wires melting together. It might be too late.

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Scratch that. The wiring from the 83 has a burned ground as well. I think it's the part that connects to the coil negative. It's burned at least 12 inches down the harness.

Not being an electrical genius, what's the best way to test for a short to ground?

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If you have wires smoking with the ignition on, it looks like you already have too many grounds. Find the "extra" ground (the short) and the proper ones might work correctly.

You may have already created new shorts from wires melting together. It might be too late.

Funny, but sadly true.

You might just start by disconnecting everything in the area of smoke and reconnect on-by-one to isolate the shorted system(s).

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Not being an electrical genius, what's the best way to test for a short to ground?

The safest way to test for a short to ground coming from under the dash, without letting more of the smoke out is this: Pull the fuses from your fusebox. This will isolate the individual circuits, allowing you to pinpoint the short. Using a multimeter or a simple test light, connect one lead to the battery (+) and use the other lead/probe to check each fuse cavity/holder. If the test light glows, you have found the bad circuit and also determined which side of the fuse the circuit is shorted to ground. It is then just a matter of following the circuit until the cause is found. A wiring diagram will be helpful also. There are often many points in a particular circuit that enable you to further isolate a short to ground, such as disconnecting a connector. You just have to get in there and use the process of elimination. Don't pull out your dash prematurely, its probably not neccesary. You will gain more knowledge by systematically testing for a short to ground, than having us guys play guessing games. As already stated, good grounds are very important also.

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Great! The smoke is coming from inside the dash. So I guess the dash has to come off

Examine the fusible links first. Didn't you say that they are in the car? If you're lucky it may be a fusible link that was melting, like it's supposed to, not your harness wires. The insulation on the links doesn't melt completely, just the wire inside, so you'll need to take a good look at them. I don't know if they smoke when they go or not. If you find a bad link, figure out what wires it feeds and follow those out to find the short.

If all of your links are good, expose the ignition switch and wires on the steering column. If you had smoke, you should have bubbled, melted looking insulation on a wire or two. Look at the wires by the fuse box and fusible links.

Edit - I was writing as Geezer was posting. I think we're on the same page though. You need to find the circuit that is shorted before you start tearing things apart.

Disconnect your battery until you find the melted insulation. Don't use the smoke to find the short. More smoke just means more damage.

Edited by Zed Head

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Update: found the burning wire. It's the Black wire with white stripe. It's the wire that goes from the neg terminal of the ignition coil to the ignition switch. It has burned away the insulation way up into the harness and it looks like it was fused with the White wire with black stripe. I'm trying to get the dash off but it's a chore. Is there a post with instructions on removing the dash?

I really appreciate your help guys!

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