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Old 03-28-2021, 06:02 PM   #1
drj434343
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Default Flickering interior lights/gauges/engine after driving; 93' 240

I'm troubleshooting an electrical issue on my 1993 240 wagon. With the engine running, I see fast voltage drops in the cabin on my VDO volt gage, my interior lights (dimming), and a separate voltmeter hooked up to confirm the issue. The drops are fast and recover fast, like a flicker.

The problem is always there, but gets really bad after driving the car for a long time, and when loading the electrical system. Turn signal relays are especially bad, and can drop voltage to the bottom of the VDO gauge every click.

Putting a voltmeter on my battery and on the alternator terminals while this is happening shows a nice steady voltage of between 14 and 13.5. I don't see the flickering symptoms like I see inside. Also note that I've tried two known working alternators (both Delco 100A units), and have also replaced my battery, but the issue remained unchanged.

I've been through and cleaned the major 12V connections under the hood, including both ends of the ground cable, the engine ground to chassis, and the 12V connections to the alternator and starter.

Today, it got so bad, that the car actually totally died while driving for a split second, like I pulled the keys out.

I'm thinking corrosion somewhere on the 12V feed into he cabin fuse panel? I've been through the fuses themselves and nothing stuck out as a real issue. I also checked and cleaned the 12V distribution box on the drivers sidewall, but that also looked pretty clean and didn't affect my issue.

On my Vanagon, there is a common 12 V ground tree that can cause systemic issues like this, but my experience with the 240 is that everything has a local ground, so a system wide issue is more likely on the 12V side?

Looking for advice on where to look next.

Last edited by drj434343; 03-28-2021 at 06:11 PM..
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Old 03-28-2021, 06:14 PM   #2
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Today, it got so bad, that the car actually totally died while driving for a split second, like I pulled the keys out.
check igition switch
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Old 03-28-2021, 07:26 PM   #3
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Awesome suggestion. I just pulled the switch and bench tested it. Position II and III connections all show low resistance, but because this problem appears to be heat and load related, I'm guessing bench top testing is not going to show a smoking gun.

I'm going to throw a new one in and see what that does for me.
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Old 03-29-2021, 06:17 PM   #4
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A bad voltage regulator or worn out brushes can cause flickering in the lights. Looking at it with one of those 52mm vdo volt gauges won't see the flicker because the gauge movement is dampened.

The ignition switch can also cause this kind of weirdness as apache suggested.
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Old 03-30-2021, 12:31 PM   #5
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Yeah, the first thing I suspected was the alternator. I even had an oscilloscope on the battery, alternator, and then on a 12V source inside the cabin. I could really only see the flickering/voltage drops on the in cabin stuff. Despite that, I still changed the alternator and then the battery to no effect.

I don't know why the ignition switch didn't occur to me, but I'm hopeful that's the fix. I've never had one go bad on any 240 I've owned, but this one has 300K miles and the switch looked to be original when I removed it.
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Old 03-31-2021, 03:47 PM   #6
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Do you have the fuse box on the +battery terminal? That terminal can corrode and cause electrical issues. I replaced the battery terminal part with a gold plated marine terminal and cleaned the rest of it. Also when was the last time the stock fuse box was cleaned? Volvo started using the pot metal fuses which corrode much faster than the copper and brass versions.
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Old 04-06-2021, 01:20 AM   #7
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Well, after a week of waiting for IPD to ship me the switch across town, it hasn't effected the issue. Still getting flickering even with a new switch.
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Old 04-06-2021, 05:35 AM   #8
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Quote:
Originally Posted by dl242gt View Post
Do you have the fuse box on the +battery terminal? That terminal can corrode and cause electrical issues. I replaced the battery terminal part with a gold plated marine terminal and cleaned the rest of it. Also when was the last time the stock fuse box was cleaned? Volvo started using the pot metal fuses which corrode much faster than the copper and brass versions.
I'm wondering if a compromised stim wire could also cause the same effect ?
Reckon it couldn't hurt to do voltage drop tests on the batt/starter/alternator wires, in case of internal corrosion ?

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Old 04-06-2021, 08:52 AM   #9
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My guess here is the exciter circuit high resistance/not working. IME denso alternator will 'work fine' without it but when engine RPM dips it will cut out and back in charging which was noticeable to the driver as a light flicker & sometimes large engine stutter.

the turn signal thing is odd though, no idea about that. make sure you measure voltage drop between components as well.

Did you rebuild your denso? I am also dealing with a slight constant flicker through 2 different 100 amp alternators and internet-sourced regulators (and one old OE one) at idle. I think we can no longer get quality rebuild parts for em that can take the heat under the exhaust manifold in a 240. Unless something else is wrong with my car which is quite possible.
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Old 04-06-2021, 09:49 AM   #10
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During my initial troubleshooting, I went through all the battery leads under the hood, including cleaning and measuring resistance. I ended up replacing the negative battery stud clamp in the process. I also made sure to clean all the grounds under the hood, as well as the 12+ distribution box on the driver's side wall in front of the strut. I didn't find any smoking guns, or affect the problem. It was during those steps I also put in another Denso as well as a new battery.

The flickering happens 100% of the time, but at least initially upon cold start, it is relatively minor. You can just see the VDO gauge needle slightly flick around randomly, less that 0.5 V back and forth. The flicker is also just barely noticeable out of the corner of your eye on gauge lights. As I drive the car, it gets progressively worse, either based on engine temp or time. As it gets worse, increased loads will cause more and more drastic voltage dips.

If it were just the Denso, wouldn't my battery at least prevent drops below 12V? That's why I thought the ignition switch suggestion was so spot on.

Does anyone know where the main lead to the fuse box goes? I'm wondering if there is a 12+ junction somewhere under the dash I haven't touched yet?

Both Denso units I put in were known working but used. I just rebuilt the second Denso with all new parts, and could swap it in, but my gut says that won't fix the problem.
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Old 04-06-2021, 09:53 AM   #11
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Originally Posted by Otto Mattik View Post
I'm wondering if a compromised stim wire could also cause the same effect ?
Reckon it couldn't hurt to do voltage drop tests on the batt/starter/alternator wires, in case of internal corrosion ?

Otto, what's a stim wire?
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Old 04-06-2021, 01:43 PM   #12
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On the left inner fender is a black covered junction block. That is where one of the smaller red wires on the batter go to. It provides the key off power to the fuse box and to the ignition key. You could be getting some flicker due to corroded connections inside the junction.
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Old 04-09-2021, 02:59 AM   #13
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Originally Posted by drj434343 View Post
Otto, what's a stim wire?
the smaller red wire, it runs to the dash & off when alternatr charges. Without being there in person I'm only guessing, ...a continuity check never hurts(not saying this is your problem but k.i.s.s..) * alternator foto

https://imgur.com/QyaUSDT




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Old 04-09-2021, 03:22 AM   #14
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Did you replace the fuses or just check them? I saw a similar issue with a cheap fuse cracking and vibrating, the connectivity got worse as it warmed. It didn't last as long as your issue has though.
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Old 04-09-2021, 08:40 AM   #15
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do you have a volt meter that can measure the RMS AC voltage? the cheap ones unfortunately cannot. After reading this thread i have been hyper focusing on the lighting flicker at idle and measuring the AC volt i have about 0.175 at the cigarette lighter. Reving it up, it calms down to 0.050 AC volt. All at the seemingly normal 13.8VDC.
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