Lotus Elan

Hot wiper ground wire

PostPost by: collins_dan » Sun Sep 11, 2011 10:05 pm

I replaced my S4's wiper motor 2 years ago and replaced the dash and switches this winter. At first the wipers did not work at all with the new switch, then someone on the forum that has also installed the new wiper switch said to connect the two center prongs, as the original had no center prongs, just a metal band connecting the two center positions. That did half the trick. The wipers work in fast mode, although not all that fast, but not in slow mode. As I rarely drive in the rain, I thought that was good enough. I traced the ground, which was connected to the courtesy light switch in the door. I tightened this up and the speed improved enough to be ok for me.

Today I was caught in a major downpour and the wipers were doing ok, but I reached down to see if I fiddled with the ground, if that would make them run faster and discovered that the ground wire was very hot. Is this a sign of a bad ground, or has connecting those two prongs caused this? I suspect that the courtesy light switch is not the original ground location either, so maybe this is the problem. I'm an electrical dummy, so if someone could suggest possible causes and a course of action to remedy, it would be most appreciated.

Thanks, Dan
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PostPost by: CBUEB1771 » Mon Sep 12, 2011 1:05 am

collins_dan wrote:Is this a sign of a bad ground, or has connecting those two prongs caused this?

I have not had a chance to look at the schematic so I can't answer about the switch connections. The hot ground wire is not indicative of a a bad ground. It is indicative of too much current passing for the capacity of the wire. Bad grounds inhibit current flow via high resistance.
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PostPost by: alan71 » Mon Sep 12, 2011 9:16 am

It sounds like a poor connection. The ground is via the courtesy light switch so it relies on the switch fixing screw holding the 2 ring terminals together. I would solder both ground wires to a single terminal. The original wire should handle the current without getting hot, the wiper motor only draws 2 -3 amps.

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wiper earth.jpg and
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PostPost by: CBUEB1771 » Mon Sep 12, 2011 11:03 am

I must correct myself on my earlier post. An bad ground will become hot due to its high resistant and warm the wire through heat conduction. If you have a long ground wire and it is hot near the grounding point but cooler near the switch then I would suspect a bad ground. If the wire is uniformly warm along its length I would suspect an incorrectly sized ground wire.
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PostPost by: collins_dan » Mon Sep 12, 2011 12:47 pm

Thanks for the help. I did not check the full length of the wire, but it is original, so I suspect sufficient for the load. I'll look further into how the courtesy light switch is grounded. Anyone with an S4 have the same ground location? When I looked at the schematic at showed the ground location as being the main behind the dash ground location, which I have never been able to find on my car. Seems one of the previous owners abandoned it and distributed the grounds throughout the back of the dash (courtesy light switch, back of water/oil gauge...). Thanks, Dan
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PostPost by: alan71 » Mon Sep 12, 2011 4:41 pm

The door courtesy light switch earth is connected to a multi-way bullet connector behind the dash which is connected to the chassis at the lower dash mounting bracket.

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PostPost by: bob_rich » Mon Sep 12, 2011 7:46 pm

Hi Folks

I am starting the rewire of my December 1973 + 2S 130 and have been looking at the switch used for the wiper. Mine had the wrong type from an earlier rebuild both speeds worked but no self park. From what I can work out there are two possible switches that can be obtained but the way the contacts connect are different so direct replacement of wires into exactly the same positions may not work. I have attached a scan of how the two switch type terminals connect and the second diagram of how the one option works with the Lucas 2 speed wiper. Both switches can be wired to work however.

Also on mine the wiper was grounded to a point under the bonnet (hood?) and did not return to the dashboard but again on a 40 year old car it had had a lot of messing with so maybe mine was not standard.

anyway hope this helps but might pay to check earths anyway as this is always a week point on fibre glass bodied cars.

best of luck

Bob
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PostPost by: collins_dan » Mon Sep 12, 2011 8:14 pm

Alan, Thanks for the picture. I checked the ground connection at the dash bracket, suspecting that it was the main ground and it is tight and clean, but I will check it again. I will also check it with the wipers running.

Bob, Thanks for the wiring diagrams. In all cases 3 and 4 have been connected, so that appears to be correct. Is it possible that they are just not moving on slow. They move so slowly on fast, maybe they just can't overcome the resistance of the water on slow, which is being caused by the bad ground.

Seems like it all comes back to me needing to figure out how to ground better. I will start by running the ground to the battery negative, which I would think is the strongest ground I could expect to get. If that works and doesn't heat up, then I might relocate the ground to the back of the oil/water gauge.

Thanks again, Dan
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PostPost by: rdssdi » Mon Sep 12, 2011 9:40 pm

It is possible the wiper motor is in need of a rebuild. It may be drawing too much current. That could also explain the slow operating speed.

You should at least remove the wiper motor and bench test it to see how much current it draws. Also a good time to remove the rack to clean and re-grease.

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PostPost by: collins_dan » Mon Sep 12, 2011 9:52 pm

As I said the wiper motor is brand new and worked fine at both speeds before changing to the new switch.

If I look at your dash, which is the wiper switch? The one on the far right in the middle? I thought that you suggested connecting the two center prongs, which I have done, but it does not look like you have done?

Please clarify, thanks. Dan
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PostPost by: garyeanderson » Mon Sep 12, 2011 10:07 pm

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PostPost by: collins_dan » Mon Sep 12, 2011 10:16 pm

I will double check my wiring tonight as what Gary has listed is not the same as what Bob has.

What's interesting is the for the slow to work, either 1 and 6 is connected or 2 and 5 is connected. It could be that my previous switch was 1 and 6 (for example) and my new switch is 2 and 5. Hadn't thought of that possibility until now. Of course that only explains why slow doesn't work, not why the ground gets hot, but we may be making progress.

Thanks. Dan
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PostPost by: collins_dan » Tue Sep 13, 2011 2:06 am

Well, as one of my partners likes to say, together we make a full brain. Gary's wiring diagram was the same as mine, but Bob's switch schematic helped me figure out that my new switch might be the other variety. By fixing up the ground feeding that location, the heat went away. By reversing my connections to the switch, now slow works. A very successful operation. Bring on the rain. Thanks, Dan
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PostPost by: elansprint71 » Thu Sep 15, 2011 10:59 am

Of course if the earth (ground) wire has a high resistance, this will slow down the operation of the wipers. Before my re-wire of the car mine were two speed- very slow and even slower. After the rewire they were like a modern car. I put in lots of extra earth wiring, running effectively a "ring main" around the car.
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