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Oldcarmechanic

Engine shuts down when the head lights are turned on

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I am working on my brothers 1999 Dodge doollie, 3500 extended cab with the 24 valve Cummins Turbo Diesel. When you turn the headlights on it kills the engine. The problem is sporadic and will come and go. I pull the ASD relay and the engine will run with the headlights on, after a while, maybe five minutes it will kill the engine, when you turn the headlights back on. I have replaced both the ASD and Fuel pump relays. I also have .5 amp discharge from the battery, which I tried to track down by pulling circuit fuses, one at a time. I did not find it. I believe I have a bad ground somewhere but can't find the link between killing the fuel pump (engine dies) and the headlights being turned on. Any help!

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Double check all fuse with a ohm meter not by looking at them... Being the ASD relay only connects to the PCM I would start over there checking grounds and cables. Remember the negative cable actually connects to the PCM directly. Pepsi71ocean just got done with a wiring issue which turn out to be a mechanic that couldn't read direction properly and cut a wire when he was suppose to tap the wire. Which just happen to be the +12V supply for the PCM. It happen to do really weird things. Turn on the heater and the gauges would die.So in the same thing double check all connectors on both the ECM and PCM for problems (debris, corrosion, etc.)Might pull error code it might give a clue to what might be happening.Being that when the headlight are turn off the ground is disconnected and the headlight lead is +12V hot. So when the the headlights are turned on the ground could be flooded with 12V (weak connection) so the engine dies. So my thought on it I would chase grounds first thing... :smart:

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I agree about the grounding. So many problems with electrical systems in auto's are because of poor grounding systems. On the other hand I think there may be a defect or problem with the multi switch in the Dodge's that controls the headlights. If I change the tilt of my steering wheel I will lose the low beam headlights.

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I would also look at the wires on the bottom side of the steering column. On my 02 I recently sold I had to repair several wires that broke from years of bending back and forth. A couple wires were for the horn and cruise and one was the main power feed for the key switch.

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Finally got back to working on my brother's 1999 24 valve turbo diesel doolie with the headlights that shut down the engine. I checked all the grounds, cleaned and reassembled. I also checked wiring of multifunction switch and headlight harness. I found G102 which I believe is the ground for the PDC located on left front fender side shield under the battery box cleaned and reassembled. Testing resistance from battery ground to G102 I get 0 Ohms. I then tested from terminal 85 of the fuel pump relay socket in the PDC to the negative of the battery and I got a value of between 62 -65 Ohms. This the ground terminal for the fuel pump relay, which connects through the relay to the ECM at terminal 86 of the fuel pump relay socket.I jumpered from terminal 30 (battery) to terminal 87 (fuel injection pump) at the fuel pump relay socket and the headlights being turned on do not kill the engine. I have installed new relay which did not help. I believe that I have too much resistance from terminal 85 to ground. I wanted to run a new ground to achieve 0 Ohms resistance but did not since I was afraid of frying some other component.If anyone has 1999 - 2002 with the VP44 pump and could check the resistance between Terminal 85 of the fuel pump socket and battery ground and let me know the Ohms reading they get it would be greatly appreciated.

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I think you are all looking at this far too in depth.. His truck is just scared of the dark :smart:

It didn't answer my question but it sure did make me laugh out loud!:lol:

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Have you tried to remove the light switch from the connector and try to jump just the connections to turn on the lights?

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Finally got back to working on my brother's 1999 24 valve turbo diesel doolie with the headlights that shut down the engine. I checked all the grounds, cleaned and reassembled. I also checked wiring of multifunction switch and headlight harness. I found G102 which I believe is the ground for the PDC located on left front fender side shield under the battery box cleaned and reassembled. Testing resistance from battery ground to G102 I get 0 Ohms. I then tested from terminal 85 of the fuel pump relay socket in the PDC to the negative of the battery and I got a value of between 62 -65 Ohms. This the ground terminal for the fuel pump relay, which connects through the relay to the ECM at terminal 86 of the fuel pump relay socket.

I jumpered from terminal 30 (battery) to terminal 87 (fuel injection pump) at the fuel pump relay socket and the headlights being turned on do not kill the engine. I have installed new relay which did not help. I believe that I have too much resistance from terminal 85 to ground. I wanted to run a new ground to achieve 0 Ohms resistance but did not since I was afraid of frying some other component.

If anyone has 1999 - 2002 with the VP44 pump and could check the resistance between Terminal 85 of the fuel pump socket and battery ground and let me know the Ohms reading they get it would be greatly appreciated.

Where is the fuel pump socket? ide Ohm test for you.

Im not sure what the fuel pump socket is.

ALso the wiring is different between 98-99 trucks and 2000 and up.

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Where is the fuel pump socket? ide Ohm test for you.

Im not sure what the fuel pump socket is.

ALso the wiring is different between 98-99 trucks and 2000 and up.

The fuel pump relay socket socket that I am talking about is in the PDC under the removeable plastic cover on the left front fender well. When you take the cover and turn it over it shows what all the relays and fuses are. The fuel pump relay is the one farthest to the left. If you pull the fuel relay out, there are three terminals next to each other toward the engine. The left terminal is #85. I would like to know what the OHMs reading is between terminal 85 and battery ground (negative terminal at the battery). The truck is a 1999 3500 doolie. Thank you for your help.

--- Update to the previous post...

Have you tried to remove the light switch from the connector and try to jump just the connections to turn on the lights?

Haven't removed and jumpered the headlight switch yet. Good idea. Thank you.

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The fuel pump relay socket socket that I am talking about is in the PDC under the removeable plastic cover on the left front fender well. When you take the cover and turn it over it shows what all the relays and fuses are. The fuel pump relay is the one farthest to the left. If you pull the fuel relay out, there are three terminals next to each other toward the engine. The left terminal is #85. I would like to know what the OHMs reading is between terminal 85 and battery ground (negative terminal at the battery). The truck is a 1999 3500 doolie. Thank you for your help.

--- Update to the previous post...

Haven't removed and jumpered the headlight switch yet. Good idea. Thank you.

on my relay there are two prongs in one direction, and 3 facing the opposite on a paralell. The only one that gave me an Ohm reading is the very center prong, in this relay (im assuming its 85, but the relay diagram on the relay wasn't much help.

The reading was 3.95@2000k.

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on my relay there are two prongs in one direction, and 3 facing the opposite on a paralell. The only one that gave me an Ohm reading is the very center prong, in this relay (im assuming its 85, but the relay diagram on the relay wasn't much help. The reading was 3.95@2000k.

As you said, after you pull the fuel pump relay you see the three openings are that parallel to each other and perpendicular to the engine. Terminal 85 is the opening farthest to the left, towards the front of truck, of the three that are perpendicular to the engine. I tried to attach a picture of the PDC from the shop manual, but I wasn't able to get the attachment to go through. Thanks for your help,

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hmmm, i don't think i got much out of that terminal, the only one that gave me any real readings was in the middle.it looked like this| | |----1----2The 1 is the one i got the reading of 3.95.

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