Hello all, I've been fighting an odd charging issue in my 87 XJ6. Old Lucas alternator diodes failed, so I replaced it with a Bosch AL193X... been working great till now. Alternator and voltage will be fine for a few minute first thing in the morning, but will spontaneously go to a no charge state. So 12V vs 13.8 or so.

What's really odd, is when everything is working, I get a normal battery'ignition light when I key the car on. When it's not working, I get no batt/ign light with key on.

Wires to alternator good, battery wires & ground good. 12V to brown black excite wire at alt. and full battery voltage to big wire on alt.

I know the bulb is good.

I'm suspecting a ground issue in the dash? Or maybe an ignition switch issue? Appreciate any ideas.

Thanks!

 

Off the cuff it sounds like an alternator problem and not a car problem, if you get what I mean.

However…

Charging oddities have occurred if the connection to the “+” junction post in the firewall is dirty or loose. The alternator output goes directly to this post. If you have a LHD car it’ll be sorta below the brake booster.

Also check resistance of the heavy alternator output wire. They can pack-up with corrosion under the insulation.

Cheers
DD

 

Thanks. Wire resistance looks good and post on firewall below brake booster is clean and dry. Took it apart and checked that early on in the hunt. Odd that I get no ignition lamp? Looking at the diagrams, it looks like that lamp is fed power from the ignition switch... maybe ignition switch or instrument grounds related?

 

Ignition switches on these cars do give trouble over time. Sometimes giving the wires at the back of the switch a simple jiggle test gives a clue.

Same with the bulb fixture itself. The warning light cluster is not overly robust. Remove the lens from the warning light cluster and give the bulb a little jiggle.

As for grounds, the ground for the warning lamp comes from the alternator itself via the exciter wire. This changes to "+" voltage when the alternator begins charging.

And the alternator itself must be grounded

Cheers
DD

 

Interesting... didn't realize the bulb was grounding through the excite wire at the alternator. Maybe I've got a grounding issue at the alternator.
When the car is cold, it works. Batt light in dash with key on and charging 13.8v. As soon as it heats up, no batt light no charging.

I'll investigate the alternator grounding and update.

Thanks!

 

the firewall Alternator Post that Doug mentions, crosses into the interior side of the firewall, where a thick Brown, always hot + wire connects to, and branches to ignition switch, and headlight switch.

Difficult to see and reach, (you have to lay on your back with a lamp), but this Main Brown wire with a ring terminal at the firewall end connecting to the Hot Alternator Post, is also tightened by a nut. 12 or 13mm if I recall.

if the nut is loose, you get strange symptoms.

if you decide to check the nut's tightness, disconnect the Battery FIRST, otherwise putting a metal wrench to the Post nut can cause a short circuit.

 

Quick update... Solved my charging issue. The voltage regulator in my new Bosch alternator failed. Was able to replace it without having to pull the alternator back out thankfully.

Appreciate all the help.

The telltale sign in my case was the batt light not lighting with the key on. So if you know the bulb/circuit is good, but the alternator won't ground with the key off, suspect voltage regulator!

Thanks everyone