Lmackattack Posted December 28, 2010 Share Posted December 28, 2010 Chasing a wireing problem on my RS.I have Hi beams but no low beams. I flip the dash switch up and my center cab lights go on but I have no low beams. Step on the Dimmer switch and the hi beams come on.. Power is at the dash and at the floor dimmer switch, when I step on the dimmer switch it does move the power to both terminals for hi beam and then back to just one terminal for low beams. I think I lost power between the dimmer or the dash switch. I say this because I cant locate the low beam power at the terminal strip on the fire wall.Hi beam power is there.. Im Not sure how the the wires run between the dash,dimmer and fire wall... any hints..... Quote Link to comment https://www.bigmacktrucks.com/topic/17033-r-model-headlight-wiring/ Share on other sites More sharing options...
David Posted December 28, 2010 Share Posted December 28, 2010 Trent,The R Wiring Diagram I have shows 14BN-Y going from the dimmer switch to the headlamps. It does not go through the block on the firewall. Power to the dimmer switch comes from the dash switch via 14BN-G. It looks like you lost power between the dimmer switch and the headlamps. Hope this helps. Quote Link to comment https://www.bigmacktrucks.com/topic/17033-r-model-headlight-wiring/#findComment-69328 Share on other sites More sharing options...
Lmackattack Posted December 29, 2010 Author Share Posted December 29, 2010 thanks David I will chase the dimmer-headlamp wires.... Quote Link to comment https://www.bigmacktrucks.com/topic/17033-r-model-headlight-wiring/#findComment-69351 Share on other sites More sharing options...
fifth wheel Posted December 29, 2010 Share Posted December 29, 2010 The circuit for the round B/R lamps is, ground to low filiment (low beam), ground to high filiment (high beam).Power up a lamp on the bench with both filiments and see how hot it gets. Seems to be a switch problem, the R model headlamp switchs don't have a long life, and I have to change them often.FW Quote Link to comment https://www.bigmacktrucks.com/topic/17033-r-model-headlight-wiring/#findComment-69360 Share on other sites More sharing options...
David Posted December 29, 2010 Share Posted December 29, 2010 The circuit for the round B/R lamps is, ground to low filiment (low beam), ground to high filiment (high beam).Power up a lamp on the bench with both filiments and see how hot it gets. Seems to be a switch problem, the R model headlamp switchs don't have a long life, and I have to change them often.FWIt's not the switch because his hi-beams work. Quote Link to comment https://www.bigmacktrucks.com/topic/17033-r-model-headlight-wiring/#findComment-69361 Share on other sites More sharing options...
fifth wheel Posted December 29, 2010 Share Posted December 29, 2010 The buddy/Thank you switch is part of the headlamp circuit,but as stated earlier it is not a switch issue.No further comments your Honor.FW Quote Link to comment https://www.bigmacktrucks.com/topic/17033-r-model-headlight-wiring/#findComment-69363 Share on other sites More sharing options...
redington Posted April 11, 2011 Share Posted April 11, 2011 If you do not have the problem solved by now this may help, There is a good chance that your stranded wires have broken but the insulation is still intact. Try a jumper from the dimmer switch to the low beam tab on the light. Also make sure that the terminal on the firewall is hot. You can use a meter or a test light to find this problem. It sounds like it is in the wire that runs from the dimmer to the left headlight. If you have a proper meter you can follow the wires and find the break. Corrosion within the wire can cause a dim light or none at all. On the RS model the wires go to the left light and then over to the right. If the left wiring fails then the right does not work so that will help isolate the problem. Quote Link to comment https://www.bigmacktrucks.com/topic/17033-r-model-headlight-wiring/#findComment-75940 Share on other sites More sharing options...
Rob Posted April 11, 2011 Share Posted April 11, 2011 I've changed all four of my dimmer switches on the floor on R models for the similar problem you are experiencing. That switch uses the upper spade terminal for voltage input through the toggle switch and circuit breaker in the dash. It then swaps terminal lugs which are left and right on the lower part for high, and low beams. I don't have power applied to both filaments at the same time. The ground for the bulbs is obtained back at the terminal strip just to the left of the steering column on the firewall. As Fifth Wheel mentioned all the switches seem to have a short service life. There is a lot of current that passes through them.If you are having problems my suggestion would be to remove the wiring harness complete and rebuild it. Vibration kills wire at connections over time as does corrosion. These old trucks have plenty of both.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/17033-r-model-headlight-wiring/#findComment-75942 Share on other sites More sharing options...
Paulie Posted August 27, 2022 Share Posted August 27, 2022 Do you have a copy of the wiring diagram? I have a 1985 mack R688T and dash lights do not work Quote Link to comment https://www.bigmacktrucks.com/topic/17033-r-model-headlight-wiring/#findComment-507647 Share on other sites More sharing options...
mrsmackpaul Posted August 27, 2022 Share Posted August 27, 2022 The dimmer knob beside the headlight toggle switch is crook by the sounds of it Paul 1 Quote Link to comment https://www.bigmacktrucks.com/topic/17033-r-model-headlight-wiring/#findComment-507719 Share on other sites More sharing options...
mowerman Posted August 27, 2022 Share Posted August 27, 2022 Years ago some tweaker lifted all my brass cables off of my DM years in years later I am trying to figure out how to hook up lights generator and heater don’t know where to start sets this cocksucker took all the wires I am lost I do have a wire diagram but I don’t know if this truck was ever switched over to negative ground now I’ll never know Quote Link to comment https://www.bigmacktrucks.com/topic/17033-r-model-headlight-wiring/#findComment-507733 Share on other sites More sharing options...
mowerman Posted August 27, 2022 Share Posted August 27, 2022 Well I’ve got plenty of time to figure it out truck is not going anywhere for a while I am just still furious Wife was bringing me to the hospital for back surgery I saw this asshole walking around the street this prick even took some thing off the sprinkler system and flooded the entire backyard at the same time my wife was freaking out and there was nothing I could do coming out of surgery the world will never run out of idiots….. bob Quote Link to comment https://www.bigmacktrucks.com/topic/17033-r-model-headlight-wiring/#findComment-507734 Share on other sites More sharing options...
mowerman Posted August 27, 2022 Share Posted August 27, 2022 Forgot to mention luckily my neighbor was home and he knew what to do with it to get it turned off Quote Link to comment https://www.bigmacktrucks.com/topic/17033-r-model-headlight-wiring/#findComment-507735 Share on other sites More sharing options...
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