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502 EFI to HP 500 carb constant alarm need wiring help

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502 EFI to HP 500 carb constant alarm need wiring help

Old 06-07-2021, 09:28 PM
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Default 502 EFI to HP 500 carb constant alarm need wiring help

Sorry guys if this is somewhat easy, but anytime I try to use the search I get 5k unrelated threads to search through.

Removed a 502 Mag MEFI 1 cool fuel II engine and replaced it with a HP 500 carb. Had the local mechanic do the engine swap a few months ago. Didn't have an exhaust at that time, so he never fired it up.

When I started it, I have a constant alarm buzzing. 40 psi of oil pressure at idle, water temp doesn't even reach 120*, and out drive reservoir is full and brand new. (old one leaked after engine swap)

There are a few more sensor/senders on the HP 500 VS. my 502 mag.

The Thunder volt distributor was replaced with a MSD. I'm guessing a few of the wires not attached have to deal with that.


oil temp sender, correct? Wouldn't cause alarm?

New reservoir wires connected. Looks to be tan with blue line and black. Is this correct?

Got 2 purple with white line wires here. One bullet connector and one eyelet. Not hooked to anything

White red line white green line solid gray

These are the ends someone spliced onto the wht/red wht/grn and solid gray

These are coming from the out drive. Maybe something to do with the Mercathode?
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Old 06-07-2021, 09:29 PM
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Also have 2 what looks like water temp senders.

One in the thermostat housing and one in the intake manifold.
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Old 06-07-2021, 09:30 PM
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If anyone can help identify these wires or suggest what might be tripping the alarm, I'd greatly appreciate it. Thank you
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Old 06-07-2021, 09:40 PM
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Obligatory porn pic
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Old 06-08-2021, 01:44 AM
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All the wires for the alarm system are tan and blue. The alarm sensors are separate from the gauge sensors. The only sensors on an HP500 are for low drive lube, low oil pressure and high water temp.
Pull the wire off each alarm sensor one at a time and see if the alarm quits. If it does not quit, then one of the tan and blue wires is grounding out somewhere. I had it happen once and a spliced wire had come apart and the wire was touching my intake manifold and grounding out. This completes the circuit and sets off the alarm.
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Old 06-08-2021, 06:53 AM
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The Thunder volt distributor was replaced with a MSD.
The TBV had one additional Tan/Blue which going to the TBV module. Having ignition replaced with MSD, look for what was done with that connection
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Old 06-08-2021, 07:04 AM
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Perhaps the drive lube level sender was disturbed with engine swap?
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Old 06-08-2021, 06:17 PM
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Originally Posted by Griff View Post
All the wires for the alarm system are tan and blue. The alarm sensors are separate from the gauge sensors. The only sensors on an HP500 are for low drive lube, low oil pressure and high water temp.
Pull the wire off each alarm sensor one at a time and see if the alarm quits. If it does not quit, then one of the tan and blue wires is grounding out somewhere. I had it happen once and a spliced wire had come apart and the wire was touching my intake manifold and grounding out. This completes the circuit and sets off the alarm.
Will do. Thanks for that

Originally Posted by AllDodge View Post
The TBV had one additional Tan/Blue which going to the TBV module. Having ignition replaced with MSD, look for what was done with that connection
Did not know this. Will lokk into it. Thanks

Originally Posted by Revelocity View Post
Perhaps the drive lube level sender was disturbed with engine swap?
reservoir was replaced after the engine swap. Thank you
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Old 06-08-2021, 06:25 PM
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check that the float in the reservoir is not stuck to the bottom. had that happen once, drove me up the wall trying to find it.
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Old 06-09-2021, 03:57 PM
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I wondered about that. I'll try that out too. Thanks
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