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Falcon6

91 Ls400 Won't Hold A Charge

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Hello All,

I have a 91 LS400 and I have been dealing with electrical issues for some time now. Here's what happened:

1. Driving to work one night, all dash lights came on and car coasted into parking lot.

2. I replaced alternator and battery and lights still didn't go out but "flickered" off and on randomly.

3. I then added an additional alternator wire in case the original's fusible link was burnt. The car ran with the flickering

dash lights for about 2 months.

4. Car died again.

5. Had the batt and alt tested and both were bad. Due to the alt not being able to charge the batt sufficiently, the batt died

and i'm not sure how the remanufactured alt went bad.

6. Replaced both again. This time I followed up on a post I read about the ground wire going through the left trunk hinge. I

found it and replaced a section in it and several other of the wires there that were brittle and stiff.

7. Result? Dash lights still on. car still died.

Now My Questions:

Can anyone tell me where all the ground wire locations are? I was putting the alternator in and noticed a grounding strap on the passenger

side of the engine bay. Are there any others? Has anyone had this problem before? How did you fix it?

Thanks

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Before doing anything else please check the 120A fuse in the engine bay fusebox and see if it has blown if it has replace it ( fuse box out to do it as it is hardwired to the fuse carrier)

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If you have a DVM you can make a couple of measurements to test integrity of the ground and charging wires.

  • Measure from the -ve battery terminal post (the post not the connector attached to the post) to a good clean ground on the frame or engine. Take a voltage read in running an loaded state (see below). If the voltage is < 0.3 V in both cases you have a good ground.
  • Now measure from the alternator power output point the the +ve of the battery. Measure running and loaded conditions again. If the voltage at loaded is significantly higher than running then the link from alterntor to battery may be corroded, loose, or some of the wire strands in the cable broken.

If you see voltage drop under load that indicates a problem in the link. Often just a loose wire or a corroded connection. A wire brush and retorquing can go a long way.

Running, engine running but everything electrical switched off except those you can't switch off.

Loaded, engine running and everything that can be switched on (high beam headlamps, audio, bun warmers, rear defrost, AC, AC blower motors high, and so on)

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Thank you sooooo much! That's great info and I will try it soon. I'll check back to let you know what happened.

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