Dome Circuit (Constant 12V) repeatedly blows fuse

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All,

1990 HDJ81, RHD

I recently installed an ATOTO F7E head unit, which replaced a PO installed Kenwood single din. It works for a while, then randomly blows the dome circuit breaker under the hood, has happened twice now. First it was only slightly blown, causing a voltage drop. Next time it was a clean break.

Now, I know logic says if you just installed a new head unit... then that is your problem. If I had replaced stock, I would agree. The PO had a single DIN, old Kenwood h/u, which would randomly go into "protect mode", which as I understand indicates a fault/short either inside the h/u or the speaker system. A hard reset would take care of the error. The PO had also run the constant power input directly from the left battery with an inline 15A fuse, I took that out and used the factory circuit. Could it simply be that the new h/u draws more than the circuit should handle?

The install of the new unit was pretty clean, all unused wires are separated and insulated. Sound is good when it works, no buzzing, ground is solid on the factory location.

Common fault locations that might cause this?

V/r,
Clay
 
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Could it simply be that the new h/u draws more than the circuit should handle?

You're not using any external amplifiers?

The Amazon listing for that head unit clams 4x24 watts RMS. That's 8 amps at 12V. According to the EWD, the dome circuit is only 10 amps. Also, the EWD says that the radio is fed by both the dome and the cigarette lighter circuits. I don't know how sure how the current usage is divided up.

Unless you're using other stuff on the dome circuit at the same time as the head unit, I really doubt that it's drawing too much current, unless it has a short internally.

Personally, I'd be looking at all the other things on the dome circuit, looking for a short.

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Run a new power wire from the battery for your headunit. Factory wiring is already undersized and 30 years of corrosion isn't helping.
 
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If your truck/radio came with an external amplifier, that needs to be removed/unplugged.
 
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If your truck/radio came with an external amplifier, that needs to be removed/unplugged.
+1 I've got an LX that has the Kenwood amp under the dash on the passenger side and I remember reading (not sure where) that replacing the HU may cause problems with the OEM amp.
 
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+1 I've got an LX that has the Kenwood amp under the dash on the passenger side and I remember reading (not sure where) that replacing the HU may cause problems with the OEM amp.
Yep, the problem happens when you bypass the factory amp. The amp stays powered on, and it stays connected to the speakers unless you unplug it. Both amps see each other as a zero-ohm load, which explains the "PROTECT" mode activating.
 

LandLocked93

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The PO had also run the constant power input directly from the left battery with an inline 15A fuse, I took that out and used the factory circuit.
Suggest the original radio and dome light - for which the wiring was designed to power - probably drew equal amounts of current at new. IMO, the separate run that was in place was a better idea (if it was 12ga or larger).
 
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Thanks for everyone’s input.

I’ve disconnected the factory amp, which drastically improved sound quality as well, and I’m running power to it on its own circuit via my new Blue Sea fuse box.

No issues since disconnecting factory amp though.
 

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