This one is curious....Hope there is no Mother-Ship hovering nearby...Those pesky abductions can be trouble......
Could you describe the pulse..? Is it a rapid flicker or slower changing rate ? ...I guess what would be the number of times per second you could estimate and does it change frequency or level according to the electrical load...?
You could try pulling the fuses one at a time while it is running to see if you get to one that changes it.....

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1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)