Eneto-55 Posted June 25, 2020 Report Share Posted June 25, 2020 Preparing to build a new wiring harness for my P15. Wondering what wires to add. (Sticking with 6 volt system.) How many wires needed for turn signals, just two more to rear? Best wire routing for adding a back up light? (I would like to make provision for using a transmission-mounted back up switch.) If adding a fuse box, is the left side kick panel the best place (especially for old guys with a stiff neck)? With a fuse box, which gauge cluster wires need to run through it? If using original style cloth covered wire, are there enough additional color choices to maintain a distinction with all of these additional wires? What additional wires are necessary for an over-drive, and how best to route them? (I don't have one, just thinking of possible future changes, and would rather do it now, if it can or should be incorporated into the main wiring harness.) Any other recommendations for other things to add? (All input is welcome, even if you just want to say I'm nuts.) Quote Link to comment Share on other sites More sharing options...
50mech Posted June 25, 2020 Report Share Posted June 25, 2020 Mmm electric fuel pump wiring. Fuse box might be easiest under the hood. Should only need one additional wire per turn signal. Possibly an unused run for pedal mounted brake light switch ( I'm not a fan of the pressure type if that's what's on a p15) Maybe power for a possible buck converter. Wipers? Just spitballing. Quote Link to comment Share on other sites More sharing options...
Eneto-55 Posted June 26, 2020 Author Report Share Posted June 26, 2020 (edited) I hadn't thought of an electric fuel pump, and had forgotten about the possibility of adapting in an electric wiper motor. The "buck converter" I had to look up. But from what I saw in the one article I read (until it got into the deep math stuff), that allows you to step down, but not up. (Remember, I'm sticking with a 6 volt system.) The other thing I forgot to mention is back up lights. I've posted in other threads as well, trying to find out how that wire is routed to the later transmission-mounted switch (starting in 49). When I completely unwrapped the wire (using a LOT of twist ties to mark the spots where wires break out of the main harness, etc.) I noticed that in the under dash section a person could do part of that in a separate small harness. Then today I was looking through some boxes of parts, and came across the generator to voltage regulator harness off of my 1st series 49 P15 (which is not here - still in Oklahoma). On the 46 it is all wrapped into the main harness, but on the 49 it is separate. (Unless I accidentally wrapped it into the main one when I rebuilt the 46 harness back in 80 or 81. (I suppose it is possible, but I don't think so, because I did it basically wire by wire back then, and didn't need to get that deep into unwrapping it.) What I was getting at regarding the fuse box, is that since some thing inside the car feed off of the ignition switch, would those wires need to rout to the fuse box, then back to the secondary device? But maybe the Positive Ground is confusing me - would a fuse need to be in line with the wire that goes to ground, or the main one in the harness? (For instance, if you wanted a fuse in line for the headlights, that wouldn't really be possible, so that makes me think it would be in the harness wire. I'm probably sounding dumb here, but if I am, then I'm just being honest.) Edited June 26, 2020 by Eneto-55 Quote Link to comment Share on other sites More sharing options...
Sniper Posted June 26, 2020 Report Share Posted June 26, 2020 the factory wiring diagrams will answer most of your questions regarding fuse routing. But typically what you are calling the secondary device will be wired to one side of the fuse. the other side of the fuse will be wired to either the battery or the ignition switch. Depending whether you need a constant 6v or a switched 6v. the headlights use a circuit breaker on the head light switch and polarity doesn't matter to it. Don't let positive ground confuse you. As far as wiring goes it's not different that negative ground. the only time you need to consider it is basically for the coil and generator. Everything else is polarity insensitive. I converted my 51 to 12v negative ground. Changed the bulbs, the coil (added a ballast) and put in an alternator and regulator. That was it. Same horns, same starter. Since I do have electric wipers I had to do something about the 12V going to it. I built a current limiting circuit to slow it down. Works pretty good. You don't have much of an electrical system and not much cares about ground polarity. As for you needing electric wipers, they do make 6v wiper motors. https://dcmclassics.com/electrical/270-w-358-6v-electric-wiper-motor.html there are ways to make 12vdc out of a 6vdc source, but there is no such thing as a free lunch. If the wiper motor draws 10A at 12v then the converter will be drawing more than twice that at 6v in order to supply the wiper motor, you just ran out of generator output. Quote Link to comment Share on other sites More sharing options...
Go Fleiter Posted June 26, 2020 Report Share Posted June 26, 2020 (edited) Depending on stile of motors, maybe heater vent and wipers run opposite direction with neg. GND. Try! Wiper may or may not find their parking position. And consider the radio! Old are polarity sensitive- maybe a (strong!) bridge rectifier is all You need for neg. GND. BTW, mine came minus grounded, and I don´t know what had been adapted earlier. Wipers park correctly, but I will check the heater and fan performance. I never did so the last 25 years :)) As said of the 6 to 12 V units: They had to power an additional 12V radiator fan off a Mercedes air condition. It was compeletly unsuccessful: The fan needs > 10 A load to start and didn´t by far ever reach its nominal speed. I needed it for hot days in traffic jams, and when hot, these units perform even worse! It was rated 10 A / 12 V but never delivered that when hot. It consumed 24 A / 6V. Greetings from Düsseldorf! Go Edited June 26, 2020 by Go Fleiter Quote Link to comment Share on other sites More sharing options...
Eneto-55 Posted June 27, 2020 Author Report Share Posted June 27, 2020 (edited) Thanks for the responses. Sniper, the 12 VDC device I had in mind would just be a modern radio or possibly a CD player. Back when I started on this car, AM was fine with me, but now there's almost nothing there but political talk shows, and I cannot stomach it. If I trade out the vacuum wiper motor for an electric one, it will have to be a 6 volt one. Maybe this is not the best place to mention it, but I think I wrote in some post or another that my 49 P15 has a separate wiring harness for the generator to voltage regulator, and that I was thinking of putting some of the under-dash wires into a separate harness as well. I read something last night (on a business site that sells old-style wire) that stated that the total load capacity of a given wire is affected by the number of other wires in the same bundle - that it drops as you increase the size of the bundled harness. They mentioned this in the context of saying that their calculations showed that the capacity was decreased somewhat by adding the extra coating - the woven mesh over the modern plastic coating. It had something to do with heat dissipation, but being neither an electrician nor a mathematician, that's about as much as I got of it. Edited June 27, 2020 by Eneto-55 Quote Link to comment Share on other sites More sharing options...
Sniper Posted June 27, 2020 Report Share Posted June 27, 2020 heat is caused by resistance. Wires ought to have minimal resistance and unless you are running lots of current thru it heat will be negligible. P(watt)=voltage times current Your voltage is 6v. I(current)= voltage divided by resistance. So if you had a wire that showed 1 ohm of resistance (which would be way high) at 6v that is only 36 watts of energy. Not much heat. 1000 feet of 16 gauge copper wire has a resistance of 4.016 ohms, typically. http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/wirega.html 6/4.016= 24 watts. Remember that 24 watts is spread out pretty evenly across the 1000 feet of wire. Seems to me to be a nonissue unless we are talking a huge bundle with lots of current. 1 Quote Link to comment Share on other sites More sharing options...
TodFitch Posted June 27, 2020 Report Share Posted June 27, 2020 36 minutes ago, Eneto-55 said: Thanks for the responses. Sniper, the 12 VDC device I had in mind would just be a modern radio or possibly a CD player. Back when I started on this car, AM was fine with me, but now there's almost nothing there but political talk shows, and I cannot stomach it. If I trade out the vacuum wiper motor for an electric one, it will have to be a 6 volt one. . . I got a 6v+ to 12v- converter/inverter that I located under my dash. It feeds a 12v style accessory outlet for charging my phone and it also powers my dashcam. The specifications on it indicate that it could power a modest (low power) radio or CD player. So if your stereo power needs are low (less than about 40 watts) that is a possible way to go. I would not try to power a 12v motor from it no matter how low the power/current rating on the motor was. 2 Quote Link to comment Share on other sites More sharing options...
Eneto-55 Posted June 27, 2020 Author Report Share Posted June 27, 2020 Here's a few other modifications/additions I've thought of in the past, but forgot to mention in the initial post: Additional cabin light, maybe in the front. (All the way in the back doesn't seem too helpful for the driver & front seat passengers.) Also thought of replacing the ash tray in the back of the front bench with a light that could be turned on manually there. One more thing about the cabin light - the only door that automatically activates it is the right front. The driver can turn it on manually, but back seat passengers don't get any light unless the front door is opened. Has anyone here added switches in the C pillars, or in the left A pillar? (I'm thinking 4-door, as that's what I have.) Quote Link to comment Share on other sites More sharing options...
P15-D24 Posted June 28, 2020 Report Share Posted June 28, 2020 Ground wires in the harness. 1 Quote Link to comment Share on other sites More sharing options...
Richard Cope Posted June 28, 2020 Report Share Posted June 28, 2020 I received the following attachments from Rhode Island Wiring, they also sale the correct color and gauge of wiring by the foot. The information below was intended for a 39 Ply, I would check with them to see if they are correct for your car. Also may want to look at Ron Francis, he sells a heat shrink brading that looks and feels very similar to cloth covering and if you w called the bare bones which would probably work. Quote Link to comment Share on other sites More sharing options...
Sniper Posted June 28, 2020 Report Share Posted June 28, 2020 3 hours ago, P15-D24 said: Ground wires in the harness. Great point. When I rewired my 51 I added dedicated ground wires to the headlamps and running/brake lights that tie right back to the battery negative. But I wasn't concerned about looking stock either. Quote Link to comment Share on other sites More sharing options...
Go Fleiter Posted June 28, 2020 Report Share Posted June 28, 2020 Friday, I sent You 3 e-mails with the scans, but maybe they didn´t reach You (Today: Undelivered Mail Returned to Sender message). To my surprise, here PM allow adding attachments, so I sent You 3 PMs.- Service Manual Pages 246, 248 and 249. If You are missing one, write me at fleiter[at]t-online.de and I will try once more! Greetings! Go Quote Link to comment Share on other sites More sharing options...
Eneto-55 Posted June 29, 2020 Author Report Share Posted June 29, 2020 (edited) 22 hours ago, Go Fleiter said: Friday, I sent You 3 e-mails with the scans, but maybe they didn´t reach You (Today: Undelivered Mail Returned to Sender message). To my surprise, here PM allow adding attachments, so I sent You 3 PMs.- Service Manual Pages 246, 248 and 249. If You are missing one, write me at fleiter[at]t-online.de and I will try once more! Greetings! Go I received one of them, and then realized that I could copy the photo from your original post about this. (The one I didn't have in any of my manuals was the one that showed the wire harness routing. Not a P15, but still very helpful.) Thanks. Not sure why one would come through to me OK, but not the others. Edited June 29, 2020 by Eneto-55 Quote Link to comment Share on other sites More sharing options...
Go Fleiter Posted June 29, 2020 Report Share Posted June 29, 2020 (edited) I will try again, one after the other with some hours between them! the Personal Message, didn´t they work too? Edited June 29, 2020 by Go Fleiter Quote Link to comment Share on other sites More sharing options...
Eneto-55 Posted June 29, 2020 Author Report Share Posted June 29, 2020 (edited) Trunk light engine bay light hood ornament light (I doubt if I will, but some do.) Later: I see that the later models have a switch on the hand brake, and an 'idiot light' to alert the driver of the fact that it is engaged. Edited June 30, 2020 by Eneto-55 adding later comment Quote Link to comment Share on other sites More sharing options...
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