Mike Pappy Congleton Posted November 20, 2015 Share Posted November 20, 2015 1999 RD688S turn headlight switch on everything comes on but headlights they do come on when working intermittent switch on top of dash ????? Replaced dimmer switch on floor & light switch still no headlights Not sure which relay is for headlights but moved relays around no luck can't find any bad fuses CAN ANYONE HELP !!!!!! Quote Link to comment Share on other sites More sharing options...
Back In Black Pulling Posted November 20, 2015 Share Posted November 20, 2015 Don't know if wired the same as the old ones but maybe this will help u find problem .http://www.bigmacktrucks.com/index.php?/tutorials/article/55-r-model-wiring-diagram/Did you check back of switch? one side marker lights other side head lights. Quote Link to comment Share on other sites More sharing options...
Mike Pappy Congleton Posted November 21, 2015 Author Share Posted November 21, 2015 Thanks for wiring diagram info not sure if same I will study Yes it is a 2 sided switch but installed new one did not help I assume both side are fed with the same hot wire ????? Quote Link to comment Share on other sites More sharing options...
41chevy Posted November 21, 2015 Share Posted November 21, 2015 My R has a circut breaker for the headlights I think your RD should also. Quote "OPERTUNITY IS MISSED BY MOST PEOPLE BECAUSE IT IS DRESSED IN OVERALLS AND LOOKS LIKE WORK" Thomas Edison “Life’s journey is not to arrive at the grave safely, in a well preserved body, but rather to skid in sideways, totally worn out, shouting ‘Holy shit, what a ride!’” P.T.CHESHIRE Link to comment Share on other sites More sharing options...
Mike Pappy Congleton Posted November 21, 2015 Author Share Posted November 21, 2015 Yes it does but breaker is ok Quote Link to comment Share on other sites More sharing options...
Mike Pappy Congleton Posted November 21, 2015 Author Share Posted November 21, 2015 there is no 12V TO THE DIMMER SWITCH I think I will run a jumper wire to dimmer switch and see if lights work then ??? Quote Link to comment Share on other sites More sharing options...
41chevy Posted November 21, 2015 Share Posted November 21, 2015 First see if you have power to the dimmer at the Head light switch connector. I've seen the connectors heat up an no longer make contact. Quote "OPERTUNITY IS MISSED BY MOST PEOPLE BECAUSE IT IS DRESSED IN OVERALLS AND LOOKS LIKE WORK" Thomas Edison “Life’s journey is not to arrive at the grave safely, in a well preserved body, but rather to skid in sideways, totally worn out, shouting ‘Holy shit, what a ride!’” P.T.CHESHIRE Link to comment Share on other sites More sharing options...
68MackR Posted November 21, 2015 Share Posted November 21, 2015 Power comes from the circuit breaker to the courtesy switch then to headlight switch then the foot switch.If you have power at the breaker and no power at the light switch or foot switch check the dash mounted courtesy switch.This is not a standard two pole switch, I had to get one from the Mack dealer.One set of poles are normaly closed when the switch is in the center position, when operated this opens the circuit to turn off the headlights and clearance lights.The other set of poles are open, when operated this closes the circuit to turn on high beam and clearance lights.This is a little complicated, let me know if more information is needed. Quote Link to comment Share on other sites More sharing options...
Mike Pappy Congleton Posted November 21, 2015 Author Share Posted November 21, 2015 Thanks that may be my problem I have low voltage to the power side of light switch when I turn it on voltage goes to 0 going to check feed wire at plug first as 41chevy suggested I do maintain full voltage at the fuse when I turn it on I replaced auto reset breaker with fuse to make sure that wasn't the problem Quote Link to comment Share on other sites More sharing options...
Mike Pappy Congleton Posted November 21, 2015 Author Share Posted November 21, 2015 OK Thanks for the help Don't know how it could've happened but the wire feeding the switch was actually disconnected at the courtesy switch Hooked it back up everything seems to work fine !!! 2 Quote Link to comment Share on other sites More sharing options...
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