Excellent! Thanks for that. I replaced the battery cables with some generic ones until I can get some replacement Dodge ones. Shortly after I had those in I found the battery was also dead (hah). I replaced the battery. Everything worked much better, for a bit...
This morning I started the engine, and the grid heater cycled much faster than it used to (1-2 seconds on, 1-2 seconds off, repeating steady). My voltmeter appears to be nonfunctional but I could notice the dimming of the interior courtesy lamps and the headlamps. When I was driving down the interstate, the headlamps continued to cycle just the same - except after a while the headlights dimmed and just started to get dimmer and dimmer.
The truck is parked at home while I drive my other car. It's such a simple wiring system so I suspect the problem is something equally simple, but could my grid heater be pulling the voltage down like this? Should I hear a sound like a large capacitor charging when I turn the key? What is the control mechanism for the grid heater, a thermister or something similarly simple? I need a wiring diagram, is it something I should seek from Dodge, Cummins, Chilton book, etc?
1989 Dodge D250 LE, Cummins Turbodiesel, 2WD A727 Transmission, 370k Miles
TRE A727 | One-Pc. DS | BHAF | Fuel Heat Del. | Torza Tonneau Cover