hicrop10 Posted October 20, 2023 Share Posted October 20, 2023 My r model volt meter has a reading with the with the key switch either on or off, is this normal?Or should I be looking for a short? Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/ Share on other sites More sharing options...
Joey Mack Posted October 20, 2023 Share Posted October 20, 2023 If it was built like later models, there should be an accessory relay under the ash tray behind the center dash panel. That is what sends out all elec. power with the key ON. Key OFF, all power is cut off.. ( Headlights and Brake lights will work though). Has any electrical work been done recently by someone else? other than headlights and brake lights, does anything else turn on? A shorted wire to power, can cause this too.. Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540728 Share on other sites More sharing options...
hicrop10 Posted October 21, 2023 Author Share Posted October 21, 2023 Joey,no there has not had any electrical work.I will check the switch you are talking about tomorrow.With the key off should there be any power coming out of the switch?My electric guy tells me that the alternator has a slight draw on it.He is going to replace it on Monday.Any other throughts? Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540729 Share on other sites More sharing options...
Joey Mack Posted October 21, 2023 Share Posted October 21, 2023 the large wire on the alt, is likely coming from the starter post, which is directly connected to the batteries, therefore, that wire will have power on it. Gauges should not have power until the key is on, and then you will see the volt meter jump to 12.6 volts.. Is this a repair that you feel comfy trying to do? Maybe you could remove the wires from the alt. gauge and see which one has power on it, and then follow it to the next connection. and so-on till you find the source of the power.? There are several ways to do this, but I would have to see the truck and behind the dash.. if you un hook the wires from the alternator, does the gauge drop to zero? Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540730 Share on other sites More sharing options...
hicrop10 Posted October 21, 2023 Author Share Posted October 21, 2023 That’s what I was thinking to disconnect the wires from the alternator,will do this tomorrow,will let you know what I come up with.Tks for the help. Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540731 Share on other sites More sharing options...
Joey Mack Posted October 21, 2023 Share Posted October 21, 2023 Your welcome.. There are many ways this issue can occur.. I expect some more good suggestions will come along.. When you turn the key on, do you hear a loud click inside the dash? Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540732 Share on other sites More sharing options...
hicrop10 Posted October 21, 2023 Author Share Posted October 21, 2023 No on the click from the dash. Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540734 Share on other sites More sharing options...
Joey Mack Posted October 21, 2023 Share Posted October 21, 2023 ok,, I wish I knew your model better.. I would expect a relay to activate with the key.. I guess you will test some things tomorrow, and get back to us.. Jojo 1 Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540735 Share on other sites More sharing options...
hicrop10 Posted October 21, 2023 Author Share Posted October 21, 2023 There is a starter solenoid under the glove box. Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540736 Share on other sites More sharing options...
Joey Mack Posted October 21, 2023 Share Posted October 21, 2023 bingo!!! Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540737 Share on other sites More sharing options...
hicrop10 Posted October 21, 2023 Author Share Posted October 21, 2023 With the key off there should be no power going through it? Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540739 Share on other sites More sharing options...
Joey Mack Posted October 21, 2023 Share Posted October 21, 2023 If it is the acc relay, that would be correct.. on the big wire leaving it. The other is hot, that's the input side.. so... One hot and one not, with the key off... Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540740 Share on other sites More sharing options...
Hayseed Posted October 21, 2023 Share Posted October 21, 2023 1 hour ago, hicrop10 said: My electric guy tells me that the alternator has a slight draw on it. My 2 cents worth. is; You've got a leak (short) somewhere.....! 1 Quote "Be who you are and say what you feel...Because those that matter...don't mind...And those that mind....don't matter." - Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540745 Share on other sites More sharing options...
mrsmackpaul Posted October 21, 2023 Share Posted October 21, 2023 This is standard for R and FR models I have ever seen Paul Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540753 Share on other sites More sharing options...
hicrop10 Posted October 22, 2023 Author Share Posted October 22, 2023 No updates,I moved some trailers today and found my fuel supply pump had a cracked housing,so my electric problem is on the back burner.Going to try to do some checking tomorrow. Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540781 Share on other sites More sharing options...
Joey Mack Posted October 22, 2023 Share Posted October 22, 2023 If it's got 'Tit's or Tires' ....... It's trouble.. Good luck Bud.. Do what can do... Jojo Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540782 Share on other sites More sharing options...
blackdog2 Posted October 22, 2023 Share Posted October 22, 2023 Bad ground .......Take jumper's clamp cab & Frame common problem ......Ive seen people keep changing alt .......? 1 Quote Ed Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540787 Share on other sites More sharing options...
70mackMB Posted October 22, 2023 Share Posted October 22, 2023 Drove an Ottawa yard horse/dog/donkey/spotter/etc. that had a bad cab to frame ground. Back under a trailer and the air ride cab would bounce. The computer (for trailer moves, door numbers, yard positions) would go off just long enough so it had to be restarted. As blackdog2 said, used a jumper cable from the cab to frame and no more problems. Had the mechanic add a ground strap on at the next PM service. .....Hippy 1 Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540794 Share on other sites More sharing options...
hicrop10 Posted October 22, 2023 Author Share Posted October 22, 2023 Joey,I checked the solenoid under the glove box.It does have power to it on one post with key off like it should,key on both sides have power.Then I took the wires off the alternator volt meter still shows a reading,Then tried the jumper cable from cab to frame nothing. Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540817 Share on other sites More sharing options...
Joey Mack Posted October 22, 2023 Share Posted October 22, 2023 I really dont know why you have power to anything but the C.B. Headlights and brake light switch... I also do not remember how that truck is wired, due to not working on that era in Many years.. I guess I would check to see what else is 'live' with the key off, and decide if you want to connect then to the acc. relay on the output side.. I did see where a couple guys said that it is normal to see the gauge reading voltage with the key off... sorry that I dont have a 90+ % answer for you.. Jojo Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540819 Share on other sites More sharing options...
hicrop10 Posted October 22, 2023 Author Share Posted October 22, 2023 Going to replace the alternator since it does show a slight drain.I’m thinking taking the wires off the volt meter and trace it back to the source of power like some one else suggested.Hopefully after replacing the alternator this will fix it. Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540823 Share on other sites More sharing options...
Joey Mack Posted October 22, 2023 Share Posted October 22, 2023 keep in mind,, the big wire on the alt. is always 'Hot' hopefully you are not throwing money away... I do understand that you need to be up and running.. good luck my friend.. Jojo Quote Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540824 Share on other sites More sharing options...
doubleclutchinweasel Posted October 23, 2023 Share Posted October 23, 2023 Don't know about the 79. But, on my 70, the volt, temp, and fuel gauges were dead until the key was turned on. The schematic shows power coming off the key switch, to the low air pressure switch, and then daisy-chained to the fuel, volt, and temp gauges. Does not show a relay in that particular circuit (low amperage draw). But, that is nearly a decade older than yours. 1 Quote "Eagles may soar, but weasels don't get sucked into jet engines." Link to comment https://www.bigmacktrucks.com/topic/73450-79-r-model-volt-meter/#findComment-540855 Share on other sites More sharing options...
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