A friend of mine has a '90 V6 Toyota engine in his RV that just won't turn off! He has to get out and pull the EFI relay in order to get the truck to shut down. If he puts the relay back in, within 6 hours the battery is dead. without the relay the battery stays good. Could this be ignition switch related, or EFI related. I am not too clear on all the electronics of the EFI. Please help!
On Toyota cars, it appears the ignition switch powers an engine main relay, ignition system and a few other circuits. I would start at this switch, check for power output with it off. Also check for crossed wires in the ignition switch wiring.
Did you test the relay yet? See if there's voltage on the relay coil (to pull it closed) that shouldn't be there? Poke around with a multimeter.
The EFI Relay contacts may be welded closed, or the coil melted and it's stuck on. Or there's a bad ignition switch that isn't turning off.
If it is a Motorhome conversion as you hinted at, another thing that is quite possible is they wired up the power tap wrong for the coach battery charge line contactor, and they tapped in to get the charge contactor coil power on the coil side of the EFI relay. And the power is backfeeding somehow to hold the EFI relay on.
The above paragraph is hopelessly confusing, I know - It'll be easier to trace out than to explain.
Motorhome builders don't expend much engineering effort on design, and they are built by semi-skilled carpenters, not a car mechanic. A short between the battery line and the contactor coil line, and it would cause exactly what you are seeing.
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The LINKAGE in my ignition switch recently broke and caused nearly the exact same symptom. I had to disconnedt the coil wire from the distributor to stop the motor, then disconnect the battery to shut down the electrics.
To start the engine again, I had to reconnect the battery and start "normally" with the key.
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