likaleica Posted December 1, 2014 Author Report Share Posted December 1, 2014 Hi again guys - at risk of sounding a total klutz....... on my 39 Plymouth I'm still confused about what amperage rated 12v wire I need for the live feed from the ignition switch to my 6v headlamp switch (with a 30 amp onboard fuse). And ditto the feed from the headlamp switch to the panel light switch. My electrical supplier says 12v wire rated at 17.5 amp is correct for the headlamp switch and 5 amp is sufficient for the panel lighting. Is he right?! Thanks again fellas Quote Link to comment Share on other sites More sharing options...
Don Coatney Posted December 1, 2014 Report Share Posted December 1, 2014 This is for 6 volt but will work on 12 volts. Quote Link to comment Share on other sites More sharing options...
likaleica Posted December 1, 2014 Author Report Share Posted December 1, 2014 Thanks Don - a very useful diagram and a lot clearer than the one in my Plymouth service manual. Am I correct in thinking No 16 means 16 AWG wire and No14 means 14 AWG wire ? 16 AWG appears to be rated at 21 amps @ 12 volts for example.... Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted December 1, 2014 Report Share Posted December 1, 2014 (edited) the number represents the wire size...and the amperage you run across it is relational to the distance of the total run also...there are many charts on the internet that list the wiring not only by AWG but in low voltage DC for automotive application and the max amperage it will carry and for max length you should run this wire for that sustained load...do a few internet searches and download a chart that will suit your project...print it out and keep it with your build sheet.. just one of a number of charts you can find on the internet that maybe of use to you http://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html Edited December 1, 2014 by Plymouthy Adams 1 Quote Link to comment Share on other sites More sharing options...
likaleica Posted December 2, 2014 Author Report Share Posted December 2, 2014 Thanks Plymouthy. I did the internet search and I found this really useful wire calculator that allows you to input voltage from 6v upwards, length of cable run and the amp load - to give you the recommended wire sizes. For my 30 amp fused headlamp light switch it calculates a minimum No12 wire. So my electrical retailer was WRONG in suggesting No 16 ! http://www.gtsparkplugs.com/WireSizeCalc.html Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted December 2, 2014 Report Share Posted December 2, 2014 Very good..glad it worked out for you...maybe folks here will ear mark this page as a favorite for their needs down the road... Quote Link to comment Share on other sites More sharing options...
Dave72dt Posted December 3, 2014 Report Share Posted December 3, 2014 I earmarked the calculator, even though I have no use for it at the moment. I will take advantage of it when I get to that point. Quote Link to comment Share on other sites More sharing options...
likaleica Posted December 13, 2014 Author Report Share Posted December 13, 2014 I've now fitted the new 6 volt switch with 30 amp onboard fuse but while the side and tail lamps now work, the headlamps still don't. I'm beginning to suspect the headlamp relay is at fault..... With the old switch, I got the headlamps working fine - but after operating the switch a few times, the headlamps stayed on even with the switch in the "off" position. Assuming the switch had failed, I sourced the new one - and it was a good idea to replace a 70 year old switch in any event. Now with the new switch, the headlamps will come on only when I manually press the relay contacts under the bonnet. So I clearly have power through the switch to the relay - is the relay itself faulty ? Can I fit a modern relay to replace it while retaining the side lights relay? All advice will be gratefully received as you will have gathered that electrics are not my strong point! Quote Link to comment Share on other sites More sharing options...
Ulu Posted December 13, 2014 Report Share Posted December 13, 2014 "...after operating the switch a few times, the headlamps stayed on even with the switch in the "off" position..." This sounds like the relay was overloaded, and the contacts welded themselves together a bit. If the contact faces are burned or pitted, or you smell the lacquer burned off the coil, this will tell the story. Quote Link to comment Share on other sites More sharing options...
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