hicrop10 Posted 16 hours ago Share Posted 16 hours ago Looking for a wire chart for my 1979 r model.The alternator is not charging the battery.There is just 2 wires coming out of it.One is a ground wire going to the engine block,the other one is another one going to the frame as a ground.There’s no hot wire going back to the starter to charge the batteries. Quote Link to comment https://www.bigmacktrucks.com/topic/75806-r-model-wire-chart/ Share on other sites More sharing options...
Geoff Weeks Posted 15 hours ago Share Posted 15 hours ago Well, that is a new one on me "both positive and negative ground on the same vehicle! Quote Link to comment https://www.bigmacktrucks.com/topic/75806-r-model-wire-chart/#findComment-579873 Share on other sites More sharing options...
mechohaulic Posted 15 hours ago Share Posted 15 hours ago How is the truck set up with the batteries? ==positive post to ground or negative post? did you check wires from the starter looking for a possible burnt wire which may have been power source alt/starter chafed through was thought to be a ground then connected to chassis. alternator have a terminal marked + ? run temp new wire from alt to starter? Quote Link to comment https://www.bigmacktrucks.com/topic/75806-r-model-wire-chart/#findComment-579875 Share on other sites More sharing options...
mechohaulic Posted 15 hours ago Share Posted 15 hours ago 1 hour ago, hicrop10 said: Looking for a wire chart for my 1979 r model.The alternator is not charging the battery.There is just 2 wires coming out of it.One is a ground wire going to the engine block,the other one is another one going to the frame as a ground.There’s no hot wire going back to the starter to charge the batteries. when you say "just two wires coming out" both to ground ; are they both on same terminal or on two separate post ? same term ok. missing power wire to alt. two wires on separate terminals - back to following wires. Quote Link to comment https://www.bigmacktrucks.com/topic/75806-r-model-wire-chart/#findComment-579877 Share on other sites More sharing options...
Geoff Weeks Posted 15 hours ago Share Posted 15 hours ago Photo is worth 1000 words Quote Link to comment https://www.bigmacktrucks.com/topic/75806-r-model-wire-chart/#findComment-579878 Share on other sites More sharing options...
hicrop10 Posted 14 hours ago Author Share Posted 14 hours ago 12 minutes ago, mechohaulic said: when you say "just two wires coming out" both to ground ; are they both on same terminal or on two separate post ? same term ok. missing power wire to alt. two wires on separate terminals - back to following wires. Two separate post.One is a ground to the frame,the other is a ground going to engine block then to frame.I checked the circuit breakers and the 7 in the middle are hot on both sides,with the key off.I throught the power went from the accessory relay to the breakers,mine is the opposite. Quote Link to comment https://www.bigmacktrucks.com/topic/75806-r-model-wire-chart/#findComment-579881 Share on other sites More sharing options...
hicrop10 Posted 14 hours ago Author Share Posted 14 hours ago 13 minutes ago, Geoff Weeks said: Photo is worth 1000 words I will get them in morning.I will say this the truck has 4 12volt batteries.The 2 on driver side the positive post are on the front side,passenger side they are on the backside. Quote Link to comment https://www.bigmacktrucks.com/topic/75806-r-model-wire-chart/#findComment-579883 Share on other sites More sharing options...
mechohaulic Posted 14 hours ago Share Posted 14 hours ago 2 minutes ago, hicrop10 said: I will get them in morning.I will say this the truck has 4 12volt batteries.The 2 on driver side the positive post are on the front side,passenger side they are on the backside. far as the post being opposite in box left vs right could be just how they were installed. important issue is they are HOOKED up the SAME ! negative ground all neg post are ground , grounds from alt to block to frame should be correct. the other ground wire to frame I go with idea it's wrong. do you know history of this unit terms of who did what and when, ? new alternator ? this just started or been since ??? was worked on . 2 Quote Link to comment https://www.bigmacktrucks.com/topic/75806-r-model-wire-chart/#findComment-579885 Share on other sites More sharing options...
hicrop10 Posted 14 hours ago Author Share Posted 14 hours ago It been in the family since new.My problem is all of our mechanics have passed onto Mack heaven. Quote Link to comment https://www.bigmacktrucks.com/topic/75806-r-model-wire-chart/#findComment-579886 Share on other sites More sharing options...
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