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weird and alarming electrical issue
Went out to start the car after it sitting for about 2 weeks and was greeted by a dead battery. Opened the hood and noticed very heavy corrosion on the + battery terminal, which was just cleaned/installed about a month ago. Also was shocked to see white corrosion on all alum components on the engine,( Eldebrock intake, alternator, new compressor, and brand new shiny Ford Racing finned valve covers put on 2 weeks ago) Almost looked as if alum parts were acting as sacrificial metal like they use on boats in salt water. When I tried to start the car, the ignition switch was very stiff and actually stuck in the "start" position. Had to quickly pull the battery cables to  stop it trying to turn over. I had replaced the original AC system with a Classic Auto Air unit a month or so ago but I thought the wiring for it was pretty straight forward and I tried not to mess with anything that I didn't have to. Car has started and run fine since then and the new AC/Heat worked properly. After working the key back and forth several times, charged the battery and it started right up as if nothing is wrong. Now I can hear an intermittent "click" sound coming from under the dash with the car/switch turned off. This is the second time the battery has gone dead since the AC install but the first time I wrote it off a due to the car just sitting. Never have I seen any evidence of corrosion or electrolysis of the alum parts like this. Thinking now that I must have screwed something up when I did the A/C install but have no idea what or where to begin looking. Any suggestions?
Could it be a grounding issue in combination with an electic leak from the A/C system? Bad ground wire from the battery and/or to the engine.
Can you check with an ampmeter to see if tou have current flow when the car is off? Then disconnect the A/C wires and recheck current.

Sent from my SAMSUNG-SM-G930A using Tapatalk

        [Image: 20160929_171923_edit2_small.jpg]

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump
Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes
Here's my standard instructions for finding unwanted currents and shorts:

First, always install electrical wiring with the battery disconnected.

Physically install the underdash harness with fuses. Connect all underhood and taillight harnesses.

When ready to check out the harness, close all doors, turn off all lights, ignition key in the OFF position, accessories off, etc. Make sure both battery connectors are disconnected. Connect the positive battery cable to the starter solenoid. Leave the negative terminal disconnected from the battery. Then use a digital volt meter to measure the current draw across the battery. Place one probe of the DVM on the negative battery cable terminal, and the other probe on the negative battery post. Be sure that the DVM is set to amps, DC. If there are no shorts in the wiring connections, the reading should be on the order of 30 milliamps or less. Anything above 1 amp indicates some accessory is on; readings above 10 amps (may blow the fuse on the DVM) indicates a dead short.

If you have a short, disconnect all other wiring from the starter solenoid post where the battery connects and re-measure the current. If current drops, the source is the underdash wiring harness or the harness from the starter solenoid to the firewall. Reconnect the wiring to the starter post and then disconnect the underhood harness from the firewall and test again to isolate the source of the short.

If the short is not in the underhood or underdash harness, the problem lies in the alternator or voltage regulator. Disconnect each of these in turn to isolate the source.

If the short or high current comes from the underdash region, keep the battery negative side disconnected and remove one fuse at a time. Measure the current as above. If you now see low current, there is either a short or an item on that particular fuse circuit is on. Turn off that item and continue checking.

Eventually, you’ll have low current readings with all fuses installed and all wiring connected. This series of tests checks all of the battery directly powered systems. To check the Accessory systems, now repeat all of the tests above with the ignition key in the ACC position. The current with the key in the ACC position may be up to 1 amp or so. When all of the tests are done and no anomalous current is noted, at that time, and only at that time, is it safe to connect the negative battery cable to the battery.

Let me check your shorts!

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[+] 4 users Like midlife's post
That's a great write up midlife.
I'm actually gonna print that out and tack it on the wall in my garage so I have it there if need be.

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"If I were you...... I´d rather be me."  Tongue

Check out my video:

Midlife is da man for electric, tho, a you mentioned AC, and said this.
[Now I can hear an intermittent "click" sound coming from under the dash]
I got on my long time gone T-bird 91 different issue but yours sounded similar on the "click" to mine.
All was fine, except batt was dead in no time. A faulty relay was causing the compressor to get under tension on regular intervals, while not "on".
I don't know how the AC unit you bought gets its juice, but if its a directly connected to positive, following Randy's advises,
i'd take a closer look at this install...

73 modified Grandé 351C. Almost done. 
71 429CJ. In progress
jebus midlife, you spend a whole day testing on a harness don't you. Not that that isn't totally the right thing to do, test it all before it blows but its one thing to do it once, quite another if you do it all the time, you must be quite the patient man.
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