01 ram 3500 turn lights on engine quits. remove park light fuse, no problem. when turn on park lights trailer relay energises. remove relay truck no start. heater fan not working. hit panic button on fob and horn + heater fan cycle. cleaned all grounds. Pretty sure maybe alarm is causing issues but cannot have engine run and lights on at same time? 

Main ground points...

 

• Interior and headlights are in the driver side kick panel.
• Some exterior stuff is grounded at the driver side headlight there is a ground stud.
• Main ground for ECM, PCM and VP44 are on the passenger side battery terminal. 

Double check all fuses. Like @pepsi71ocean had his brother do some wire work and misunderstood the directions and cut the power to the PCM. Then wired up the voltage regulator for the transmission. This created a weird case where if you turned on the blower the odometer would display CCD Bus and the PCM would die and voltage regulator too. limp mode the transmission if I remember right. 

 

Use the wiring diagrams and make sure ground and power are present at the PCM and the Central Timer. 

On 2/16/2019 at 9:52 PM, Mopar1973Man said:

Main ground points...

 

• Interior and headlights are in the driver side kick panel.
• Some exterior stuff is grounded at the driver side headlight there is a ground stud.
• Main ground for ECM, PCM and VP44 are on the passenger side battery terminal. 

Double check all fuses. Like @pepsi71ocean had his brother do some wire work and misunderstood the directions and cut the power to the PCM. Then wired up the voltage regulator for the transmission. This created a weird case where if you turned on the blower the odometer would display CCD Bus and the PCM would die and voltage regulator too. limp mode the transmission if I remember right. 

 

Use the wiring diagrams and make sure ground and power are present at the PCM and the Central Timer. 

This is correct. It was back feeding the power needed to run the PCM from blower motor relay. 

 

I suspect that the OP is having a ground or a power lead chaffing together somewhere. I would start ohm testing, but I would suspect the headlight switch. Or the wiring that goes to it.