Glow plug relay "motorboating"

[cseger1]

Sorry if the term motorboating doesn't make sense. I can't think of another way to describe it though. After removing some of the "extra" wiring in my truck (PO had patched around every system with discrete wiring to the battery and inline fuses YAY!) I came out to find my battery dead. Once I got it charged up I turned the key and heard the relay come on for about 10 seconds. Then the relay started oscillating from on to off really fast, resembling the sound of motorboat. Any idea why? Thanks

Christian

[cseger1]

Actually, they're all motorboating. I think the battery is not fully charged despite the reading of 13V on the meter.

[asavage]

When a relay feeds a circuit that drags the relay coils input below latch value, the relay drops out. Immediately, the source voltage rises and the relay re-engages. Lather, Rinse, Repeat. "Motorboating" accurately describes the sound.

Low battery, bad battery, bad connection, or load that is being switched is too much for the circuit (ie a short downstream of the relay). Those are pretty much your only options.