ok my marker lights keep tripping breaker! pulled every light out and checked found some corrision on some cleaned and replaced all side marker light then they worked. Left 2 miles down road lost again any ideas or commn issues? most marker lights are led i replaced cab switch and checked connections under back step

Thanks in advance

Refitt the pump to a real truck before wasting any more $$$$$

Yes I check the boom marker lights and flasher even unhooked them still no luck. 

The hot wire to the lights is grounded to the body/ frame somewhere. Had the issue many times on mr688s Mack's ..follow the wire and replace the whole circuit, or find where it's rubbed to the truck and fix..could also be pinched behind the marker light

We've had to change out the pigtail that holds the turn signal light below the headlight on a couple trucks to make the problem go away.  Funny thing is that light appears to work fine.  I haven't had the time to look at the wiring schematic to make sense of it, but it's solved the problem on 3 or 4 trucks.   Get the entire bulb socket and 3 pin connector from mack. You may have to install the connector and pins yourself and they often come loose in the bag.  

The wiring often gets damaged to the liscense plate light inside the conduit. Also, check the connection behind the right front turn signal lamp. this is usually where the circuit is spliced into, to run the rear marker lights.

thanks prefconc, the wire rubbed through right behind license plate light easy fix

Glad to help