There are other problems that can cause the same (on briefly and then off) glow malfunction, one I can name right off would be lack of power to the relay(s). Have you checked the heavy-gauge power wiring and fusible links yet? This particular issue has been discussed here before, there may be more to it but that is my recollection.

Additionally, the plugs are not 6V, they are 12V units. The 'cold' glow supplies them with full battery voltage, while the 'warm' mode runs the current through the large resistor first. I imagine this resistor's presence in the system is where the rumor started.