BritishV8 Forum

I've started sorting out why my speedo, tach, & fuel gauges aren't working. In the process it occurred to me I may not have done my grounds right in general...  Rather than rely on chassis grounds at each component, I ran a separate ground harness.  I am, however, sharing the same ground for multiple devices - e.g., one 10Ga ground branches to multiple higher gauge grounds to various things.  I've sized the ground wires according to the feeds and the main grounds are sized according to the full load of all the devices on that ground... But, in doing this have I introduced a problem where a failure in one circuit can now bleed over into another circuit?

The grounds, by definition, all link to one point at the negative battery terminal. Whether you use a dedicated grounding buss or use the frame to do the same function, they are all still connected to the negative battery terminal. I like the idea of a dedicated grounding buss because copper is many time more conductive than steel and line resistance has to be measured over the entire circuit, not just the feed wires. I don't think the grounding buss is your problem.

Right - I'm not thinking my gauge problem is related to the ground harness - unless maybe the ground to the dash came loose.  I was just wondering in general if feedback or a high current fault on one circuit could affect the others.  Your answer says no so my ground harness should be ok.

When grounding my car, the battery is in the boot. Negative from battery connected to the frame. Ran 1" flat braided grounding cable from aluminum engine block to frame. Ran another 1" flat braided grounding cable from engine to body. This makes sure that there won't be any grounding problems down the road. I used in the engine compartment a distribution block for the positive connections, positive from battery to block, alt to block, block to starter, and block to wiring panel.Used a fuse between alt and distrbution block for protection of the charging circut. Distribution block and inline fuse was from Monster performance products for high end stereo systems.

For behind the dash I must have 15 grounds on one bolt to the body.

Haven't had any electrical problems at all.

You may have the problem on the power side instead of the ground side. Did you daisy chain the power for the lighting on your gauges and use a dimmer switch? Are you using digital gauges or analog?

RE: my gauges - there are two power daisy chains -- one for the gauge lights & one for the gauges themeselves.  They're electric analog units from AutoMeter.  The lights are working but the gauges themselves aren't.  Fuel reads empty all the time; tach on 0; and, speedo initializes indicated by a sweep of the needle & drops back to 0 and stays there.  I don't think it'll be hard to sort those out.  I've already found the first issue; may be what's causing all three to act up... speedo leads are pressing on the cross brace behind the dash.  Will fix that this weekend & see where I am after that.  This weekend I made some fiberglass pieces for the A/C system.  One is just a splitter that takes a single output from the evap box & routes to two vents; the other is a piece that let's me "remote" mount the blower offset by a few inches.  Also started installing some heat shield - way too much heat coming up through the floors.

I chased ground loops all over a destroyer many times many years ago. I don't think you have a ground issue but there's a way to check it.
Attach a battery jump cable negative lead to the negative post of the battery and locate the other end of the cable lead somewhere convenient to where you think the ground issue is. Connect that other end of the jump cable lead to a volt meter negative (ground) lead. Connect the positive lead of the voltmeter to the suspected poor ground point. Set the meter to DC volts and fire up you circuit. If you get a significant voltage reading on the meter you have a poor ground somewhere between the battery and the location of the positive meter lead. (If you get a negative reading it indicates the jump cable doesn't have a good connection)

I haven't started installing my wiring yet but for my cockpit ground distribution I'm going to use a neutral wire connection terminal strip that you find in home circuit breaker boxes.

Steve

I wanted to not have any electrical issues on the car especialy ones caused by poor grounds. I made a grounding buss out of 3/16" copper plate (right above the MSD) that all grounds from the cockpit forward will connect to. Everything in the rear of the car will ground to the negative charging / jump post I have in the trunk. The charging / jump posts are connected directly to the battery with short 1/0 cables. The horn is probably the only device I will ground through the frame. The other 2 busses to the right of the MSD are for constant power and switched power feeds. The solenoid turns power on and off to the whole car with a couple of exceptions like radio memory and electric water pump and fans if the car overheats. Both the power and ground busses are connected to the battery cables at the starter with 6 ga cable. It's probably overkill but I only want to touch the electrical system on the car once

"It's probably overkill but I only want to touch the electrical system on the car once"

You could get drummed out of the Order of Lucas for that statement.

"You could get drummed out of the Order of Lucas for that statement."

I'd have to go look but the only thing that could possibly be Lucas are the tail lights and those will probably be changed out for LED's before it's all over.

Jim, aren't you concerned about a short with the hot busses exposed like that?

"Jim, aren't you concerned about a short with the hot busses exposed like that?"

Rob

This panel is pretty well protected up behind the dash and I plan to put a plastic cover over them when it finally gets installed. It's probably less vunerable than the battery terminals that sit there unprotected.