Electrical issue please help


New Member
Jan 8, 2020
I have a 2001 mustang GT 5 spd that I bought in rough condition that I’ve been restoring, car currently has 99k miles. I rebuilt the motor and put a new ECU in it because I was told it had a v6 ecu in it by a local ford dealership (I think the guy was lying to me) when I was diagnosing a misfire issue. (Timing was off, that was the actual reason) had the new ecu flashed to my car by a different dealership. Car ran and drove great, ever since I’ve owned the car, even with the bad engine and odd ball ecu the car has has had a parasitic draw and has now ruined 2 batteries from boiling them (overcharging I assume) so I put a new alternator on and the problem stopped for a couple days. Now it does it again. Haven’t driven the car much in many months because I don’t want to keep ruining 100$ batteries. I’ve owned the car for 3 years now and I just want to drive it. Also sometimes the cluster will do some weird things. Odometer will temporarily shut off while driving then randomly come back on. Any tips would be amazing!
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SN Certified Technician
Aug 14, 2009
Houston Texas
If this were my car I would focus on the battery negative ground and the grounds to the radiator core support and the motor ground. Make DOUBLE certain that all of the grounds are solid, clean, and tight. Need to be capable of carrying heavy currents with little (or no) voltage drop.

Double check that the motor grounding strap between the left hand motor mount and the car's frame rail is in place.

What is the voltage at the battery? It shouldn't be a mystery if the battery is being over charged or under charged.

Here's some information that should help.

Howto perform charging system voltage drop test

My odometer goes on and off?
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The first widely accepted Tranny
15 Year Member
Dec 24, 2003
30 Mins from a Ragged GT
^^ Agree ^^ I had a constant draw on my 95v6 and if i didnt drive it 2x a week the battery would be dead in 4 days. So I chased the demon down to the ground wire to the body, rust and debris formed in between the semi loose connection and once I cleaned it and tightened it up, the issue was gone.
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New Member
Jan 8, 2020
Thank you guys so much for the quick replies, sure enough I checked my ground and it was corroded on the connection to the chassis. I never had it off when I pulled the motor. Put a different known good battery in it and it didn’t drain over night and I’ve put ~100 miles on it between yesterday and today and it didn’t boil the battery yet. Charging at idle about 14.5-14.7 When I first got the ground fixed and fired it up
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