Interior and exterior lights pulsing /flickering

[Jimkounter]

So I'm now the proud owner of an 1981 C3 and that's one of my life goals completed.

However, I have an interesting electrical gremlin that I'm keen to resolve. The electrics are all flickering. Interior and exterior lights, headlights, rear lights all flicker rapidly. The battery meter pulses and the battery warning light flickers on and off. On full beam all four bulbs in the headlights come on fine. Dipped, only one bulb works. Odd. Additionally I can hear a relay in the dash clicking on and off. I'm unable to check the battery with a multimeter when it's connected because there's thick rubber boots covering the entire terminal. I'm guessing that it's a ground issue - does this sound right? Any ideas where I should start looking? I've driven it for about 150 miles so far and other than the lights everything seems fine. Any help is greatly appreciated.

John.

 

[johng]

The inboard headlamp bulbs have 2 filaments (high beam and low beam). If only one headlamp lights up on low beam, then either that filament is blown or it's not getting 12 volts. It shares a ground with the high beam so it won't be that.
Do the lights only flicker with the engine running or do they also flicker with the ignition on but engine not running? If it's only with the engine running it could be a problem with the alternator or voltage regulator.

 

[Jimkounter]

Thanks John, I've just checked and it's only an issue when the engine is running.

 

[teamzr1]

Try to zoom into what the problem could be
when driving check if the radio, HVAC, cruise control, dash gauges, etc to see if they also are affected
Jiggle and move the light switch knob also

Try and twist the battery cables to see if slightly loose,
Check negative battery cable to frame is clean/tight

I have attached below the full wiring diagrams for a 1981 C3 that would help trace wiring down

 

[Jimkounter]

Thanks teamzr1, that looks not dissimilar to the wiring diagram for an electromagnetic pimball machine. That was a fun task finding a wiring issue too!

 

[teamzr1]

You're Welcome Jim

I think if you try what I mentioned in other post and find it is only the lighting is having the problem
that with engine running causing enough vibration to effect a loose wiring connection or something in the light switch

 

[Stingray]

What's the condition of your battery? Weak battery can result in flickering lights. You need to check its voltage with a good voltmeter when the car's been standing overnight and before it's started. 12.4v would indicate a weak battery and 12.2v a knackered battery. (A good battery would be in the range 12.6 - 12.9v). Best battery test of all is a high current drain test at your local battery supplier.

Next most likely culprit - alternator/rectifier.

 

[Jimkounter]

Everything flickers, internal lights, external lights, gauges etc. When there's load such as the headlights on the noisy relay clicking in the dash disappears and the battery light flashing dims considerably. I'm guessing it's an alternator issue, possibly a dodgy diode causing ripple in the current. I'm going to send it off to a specialist to have a look at I think.

 

[Jimkounter]

So I'm getting 12.9v on the battery at rest. With the engine running I'm getting around 14.6v at the battery. The output from the alternator is about 15.5 to 16 which drops to about 14 when headlights are on. I think my alternator is creating the pulses so it sounds like a rectifier problem?

 

[Stingray]

Well yes, but how good is your voltmeter - does it show the flicker? If the voltage appears stable at, say, the battery you need to check it at a flickering bulb. And check the condition of the main ground/chassis connection(s) from the battery to chassis. Composite body cars are very susceptible in this area.

 

[Jimkounter]

Quick update for anyone searching threads in the future - I replaced the alternator and everything is now fixed. The bizarre pulsing of the lights and battery gauge has gone and the battery indicator now shows about 14 volts when running rather than the 17 or so or was showing before. One job off the list and I'm looking forward to my first show at the weekend.