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1994 MACK ch 613 headlights stay on all time

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Removed dash cover where light switch is and checked voltage on female plug behind switch. Voltage  and wire number in picture . These readings were with key switch off. Headlights are on even with lights switch unplugged. Only way to lights off is to remove drl relay. This relay came out of my 1991 MACK ch613. Is there a difference between 1991 and 1994 drl relay.Everything is fine with 1991 when I put drl relay back in 1991.

I guess that 7.44 voltage  on wire 7b2.0 is what is causing problem?


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further investigating wire diagram this is what I believe I have traced. Fuse 16 gets electricity from accessory relay. Output on fuse 16 is is wire 16a20 which goes to drl. Drl output is wires 7d20 and 7e20 and 7g08.

7g08 goes to park brake drl switch.  Cannot find this switch. Maybe option???

7d20 and 7e20 goes to tilt ray relay. One of the wires on tilt Ray relay is wire 7b20 which goes to headlamp switch. This is wire with 7.44 volts which I think is causing headlamps to stay on.

when I pull fuse 16 headlamps go off. When I pull drl headlamps go off.

i am thinking tilt ray relay is not unlatching when key is off. What is the purpose of tilt ray  relay?

Other wires on tilt ray relay :

be08 which goes to directional signal switch dimmer

bb10 which goes to trailer tail Lp relay


thanks in advance


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The purpose of the Tilt Relay is to use smaller gauge wires to the headlight switch, and therefore less amperage on switch contacts.

If the DRL relay works correctly in the '91, that proves the relay is NOT sticking/defective. If the '94 uses the same p/n relay, then it is being energized by the '94 wiring. Verify the relay is correct for the '94, and that the terminal locations match the diagram. I can't read the diagram on my small screen. 

My guess (I don't warranty guess-work troubleshooting) is the switch is designed to supply a ground for the tilt relay, which then closes and powers the headlights. If this is verified by the diagram, I'd check for a "Grounded" ground wire from the relay.

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Will check with Mack on drl relay on 91 vs 94.

Drl is grounded directly to ground. Now the tilt Ray gets its ground from the trailer tail lamp relay. This relay goes directly to ground.

are daytime running lights suppose to only come when you release the brakes?

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