1974 450SEL - Electrical quirk...
 

Hey all.

So I've been driving my '74 450SEL and lately, I started to develop an electrical issue.

When cruising at town speeds (below 50MPH), sometimes, when letting off the throttle and letting the engine drop to idle speed, the gauge cluster would flicker out. It doesn't happen often, but only when there are short trips to the store or something. On the highway and at speed, it's fine.

Details:

- Tachometer would dance or die and so would Fuel/Temp/Oil pressure gauge, but speedometer remains unaffected and working
- There would be a relay click noise behind the gauge cluster every time it happens.
- It all happens like there's a lose connection or a bad ground.

- Drivability and engine performance seem unaffected

- When the gauge cluster flicks, I noticed the reverse lights also kicked in and out

- When it goes out, it goes out for a few second but all comes immediately back.


Steps to resolve:

I haven't checked the gauge cluster bulb for the battery yet (it could be out and not telling me that there's a charging system problem).

But some preliminary research suggests either voltage regulator (on the alternator or on the body) or the need for a new alternator...

I'm also thinking a relay could be going.

Any suggestions? I plan to replace both voltage regulators and just getting a new alternator since they're pretty cheap and easy to replace.

" It all happens like there's a lose connection or a bad ground." Go with your instincts.

Before you start throwing parts at your car change all the fuses to the copper/brass coloured ones if they are still the aluminum ones. Pay particular attention to fuse number 4.

Don't be too quick to change the alternator. Check to see if it is charging properly with a voltmeter. The regulator can be removed to check how much the brushes are worn. Rebuilt alternators may be cheap but most of them in my opinion are garbage unless rebuilt by Bosch. Your symptoms do not sound like an alternator problem.

Thanks for the words guys. Just needed some reaffirmation on my thought process.

I replaced all the fuses when I bought the car as part of getting it back on the road but I will double check along with everything else.

Do either of you know where the ground would be for this circuit?

This is why I love you guys....

You all help me realizing sometimes I'm over thinking stuff--ended up being dirty contacts on fuse #4

Thanks Rick for the pointer--sometimes I default to thinking it could be bigger things since I've had to deal with a few worst-case scenarios with my car hehe

ch:

Please satisfy my curiosity; while driving the car you would be able to see the flickering of the instruments, but how did you simultaneously see the reverse (aka, "back-up") lights?

Found a large empty parking lot with an office building with really reflective windows at a local corporate park on a Sunday :)

for potential issues down the road, the dash pod is grounded by its rim in the dash, sometimes overlooked but the cause of all sorts of gauge and light gremlins