6368 Posted March 16, 2020 Share Posted March 16, 2020 i'am working on a 1975 dm685sx . The volt gauge is always on. i checked the wiring diagram i have and it does not showthe gauge to be wired through the relay that comes on with the key. This doesn't seam right to me..is it? Quote Link to comment Share on other sites More sharing options...
Lmackattack Posted March 16, 2020 Share Posted March 16, 2020 My Truck was wired so it only comes on with the switch. how ever as the truck was old I decided to run a wire down to the battery as the gauge was reading lower than what the Alternator was putting out. I think the old wireing has to much resistance it it to read correctly. I was seeing a full volt lower without the new wire added. Quote Link to comment Share on other sites More sharing options...
Rob Posted March 16, 2020 Share Posted March 16, 2020 All trucks I've been around using a voltmeter are not wired through any relay and B+ is applied at all times. Easily changed to suit but I've never seen one originally like that myself in the now antique trucks. Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
6368 Posted March 17, 2020 Author Share Posted March 17, 2020 21 hours ago, Rob said: All trucks I've been around using a voltmeter are not wired through any relay and B+ is applied at all times. Easily changed to suit but I've never seen one originally like that myself in the now antique trucks. My 81 RD and any newer macks i have been in it activates only with the key on. I was only concerned about the small current draw ... not much i know but the truck may sit for extended periods of time. If i don't wire it through the relay i will probable just install a master disconnect ( probably a better option anyway). Quote Link to comment Share on other sites More sharing options...
Rob Posted March 17, 2020 Share Posted March 17, 2020 5 minutes ago, 6368 said: My 81 RD and any newer macks i have been in it activates only with the key on. I was only concerned about the small current draw ... not much i know but the truck may sit for extended periods of time. If i don't wire it through the relay i will probable just install a master disconnect ( probably a better option anyway). I can believe it. I ceased with trucking in early 1984 and everything I worked on was used and older then. Being lowest on the totem pole got me in that position time and time again with the order to not talk about wages as I made more than the other two but got things done faster. A master disconnect is a good idea as parasitic draw through leaky alternator diodes, memory retention in electronics, keep alive circuits, etc. are all an electrical draw although it should be in the milliamperes at most, but as things age, the draw can increase. Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
eddeere Posted March 17, 2020 Share Posted March 17, 2020 I installed a new wiring harness in My B 61. The voltage meter was on all the time. I changed it to the key switch. Later I installed a master disconnect switch. Quote Link to comment Share on other sites More sharing options...
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