Well-Grounded · 12 December 05

Eve had a little bit of her wiring reworked over the weekend.

Hmm, actually it was more like:

Wiring, beeping, de-wiring, beeping, wiring, beeping, de-wiring, wiring, beeping, de-wiring, beeping, wiring…

Beeping being the sound the voltmeter makes when there’s a shorted connection. In this case it was beeping out a short between chassis and system ground.

Lot’s of bleeping beeping.

As I mentioned earlier the inside wiring harness has been put back together and dressed. Well, if you can call being wrapped in black electrical tape as being “dressed up” then this is your kind of date.

Calling it a wiring harness isn’t quite right either. It’s really the central nervous system of the car’s electrical system with most of the fuses, some relays, and all of the interconnects between engine, dash, and chassis wiring.

Here’s how it looks now:

As a reminder, the image on the right is how the harness looked when it and the dash were first removed. Click the image for a larger version.

I’m feeling pretty happy about all of the stuff removed. It started off with over 30 connectors, which have been whittled down to about a dozen and an equally impressive pile of wires removed.

The last connector to be removed was an oddball grounding block. You can’t quite see it in the picture above, but there’s a about five ground wires just hanging off into space along the top edge in the middle. They were spliced into one thicker wire and a smaller wire which then went to the far right of the dash area and were grounded to the chassis.

There’s a bunch of grounding blocks scattered around the car, most of them look like this.

The block, as you can see, is just a bunch of connectors jammed onto a multi-headed jack that is then screwed to the chassis.

In looking at the Probe’s wiring manual there’s around six pages of grounding and quite a few of these blocks. Basically instead of running heavy duty ground wire throughout the system there’s smaller ground wires for most uses and then when you have heavier duty grounding needs (i.e. headlights) the ground goes straight to one of these blocks.

In fact there is no wire going from the battery ground to any of these system grounds. The battery ground is bolted to the chassis and to the transmission (providing ground to engine).

Someone wrote in the comments that I should re-wire the whole car to ensure that the ground is isolated from the chassis. I think they meant keeping the high voltage ground from the chassis with system ground. You don’t want the high voltage ground to be connected to the car’s normal ground, that’s why we use DC-to-DC converters and other steps. Bob Brant’s book covers this.

You could isolate the car’s normal ground as well, just to be doubly sure but I suspect that would make things more vunerable to static. Getting in and out of your car, especially in the winter, generates a lot of static. If you isolate the system ground you probably increase the chance of zapping electronics with stray static.

Still, I decide to explore how hard it would be to isolate ground. Removed all of the grounding blocks from the chassis…beep. Disconnected all of the wiring harnesses…beep. Turns out the headlight motors must be grounded to chassis where I can’t see. Unplug the connector, less resistance, still beep.

I was running out of things to unplug when I noticed the windshield wiper motor. Unplug the connectors…no beep.

The unit has two plugs and only one of them caused the grounding. So I took that section apart out of curiosity.

This is a switch cam. Basically as the motor turns this plastic wheel is spun around and an “arm” on the switch assembly (below) follows the channels in the cam. The motor turns until the switch is engaged, which probably reverses the motor polarity voltage and causes the motor to go the other way.

It flip flops better than a politician around election time.

I’ve highlighted the culprit for you. Somewhere in the switch box the ground is shunted over to this little metal contact, which gets pinched against the metal body of the wiper rig, which of course is bolted to the body.

After clearing that up and hooking the harness back up there were more bleeping shorts.

Inside the top of the hatchback one of the ground wires is bolted to metal, and another ground is bolted near the latch.

All in all I was eventually able to isolate ground entirely, but to really do this you need to replace all of the chassis grounds with a heavy duty ground wire, run throughout the car. I’ll stick with the chassis ground. It worked in the first EV and should be fine for Eve as well.