cause of all lights going dim ?

[JD3426]

I have a stock '72 Chevelle, 350 automatic with a console horshshoe shifter. Recently I noticed that all of the lights, dome, headlight, etc. go dim when I shift from park to drive or any other gear. I have replaced the voltage regulator with no change and am wondering about the neutral safety switch ? Any suggestions ?

[Hank70SS]

I suspect the engine rpm's drop when you put it in gear. Original alts on these cars did not put out a lot of amps so slowing the engine done could very well be the cause.

Dim lights on these cars is pretty common at idle in gear.

[JD3426]

I know what you are talking about with the low idle but this is clearly something different. It continues while driving and has just started recently.

I couldnt find anything here that sounded similar, other than the voltage regulator so I thought I'd ask.

Great site with lots of great info.

[Ms Grumpy]

It could still be the alt. is going bad. Are there any other symptoms ?

[BillsCamino]

Check all the ground connections...especially engine to body...

[JD3426]

The ground at the battery (on the fender) was loose. Fixed that with no change. Other ground locations ?

The only other symptom is the shifter. I can shift out of park and see the lights dim and brighten, they will dim when going down the road also.

I did have a GEN light come on a while back but tightening the belt eliminated that.

[Hank70SS]

Ground to fender handles everything except starter and ignition. The main ground cable from battery to engine handles those 2. AutoZone sells an electronic voltage regulator, direct replacement for the old mechanical one. They use to sell a Wells VR715 now it's sold with Duralast brand name, not sure of the new number but they can look it up.

I would start with checking your ground connections, battery connections then positive feed. Positive feed is from battery to starter. There is a main splice near the starter where positive splits off to feed the rest of the car.

[BillsCamino]

Make sure the ground from the valve cover to firewall are intact. The ENGINE needs a good direct CHASSIS ground.
The Duralast P/N on the electronic voltage regulator is the same ...VR715
I use these on ALL my externally regulated Chevelles. The cover will interchange with the original so it will look completely stock.

[JD3426]

I replaced the voltage regulator yeterday with no change. Will have to wait until tomorrow to check the rest of the suggestions. Thanks for the help.

I will have to double check but I dont remember any ground from valve cover to firewall ?

[Hank70SS]

Bill, you don't need a ground from valve cover to firewall. They were originally installed only if the car was ordered with a radio. No radio, no straps. They were intended to suppress ignition electrical noise.

Engine is grounded by the main negative battery cable. Chassis is grounded by pigtail off negative cable to passenger side front fender. So engine and chassis are tied together at the negative battery post.

I bought a set of those straps years ago just to make it look original but never got around to installing them. Been driving the car for 9 years without them with no electrical issues. If installing them solves a problem then you need to keep looking. They're covering up the fact that you don't have a good ground from the battery to chassis or battery to engine.

[BillsCamino]

Gotta disagree Hank...

Engine sits on rubber mounts...trans mount is rubber too.
I've seen quite a few tranny rear output shaft bushings ATE up trying to provide an electrical ground.
Engine requires a good CHASSIS ground...not just the small one provided indirectly by the neg battery cable.
Found this out years ago....on a '69 Elky. This car would loose power every time the clutch was pushed in. Valve cover ground cured that problem.

[Hank70SS]

Well you can look in the factory assembly manual Bill, U63 Radio-Ground Straps. Two with an AM radio and a 3rd one with an FM radio. What you call the 'small' cable coming off the negative battery cable is 10g, same size as the pigtail coming off the positive battery cable. So if the positive pigtail can supply all the power needed the negative can supply the ground for that power. GM figured that was enough to carry the load for all lights and accessories. The starter is a different story and why the main cables go directly to the starter and engine.

I can show you 10 cars without those braided cables for everyone that has them. Those braided cables were never meant to be current carrying. Their electrical theory was a little messed up but they felt the braided cables would help suppress the electrical interference from the ignition. If they were meant to carry current one regular insulated wire would have been sufficient.

Like I said, if adding those grounds solves a problem then you have a problem with the chassis ground elsewhere.

[BillsCamino]

Respectfully, I guess we'll just have to agree to disagree. ;)

My original BAL built '66 300 DeLuxe, 6 cyl w/PG. has a braided ground from rear most valve cover bolt to firewall. Also has a braided ground from lower pass inner fender to frame.
NEVER had any radio....

[Hank70SS]

Respectfully, I guess we'll just have to agree to disagree. ;)....

Respectfully, no problem Bill.

[JD3426]

Bill & Hank,
I have had no luck finding the problem so far but still looking. As far as the ground in question. My '72 came with an AM radio and has never had one. Never a problem until recently, if adding the additional ground strap solves it I guess I will be happy but also wondering what I am misssing ? I did discover yesterday that the horn is not working, dont regularly use it so am unsure when that issue started or is it is related.

Thank you both for the help.

Jim

[Hank70SS]

There are multiple ground straps on the rad core support. Headlights, voltage regulator, etc. Make sure all those are good clean solid connections. You may also want to invest in a multimeter so you can check voltage. Harbor Freight has one for 6 or 7 bucks. Not the best quality but good enough for occasional use. I would check voltage in interior of car, fuse box is good location, while idling in park then after shifting into gear. If lights dim and voltage stays pretty constant then it would be a grounding issue. If voltage drops significantly, several volts, then more likely a charging system or positive wire issue. I would want to know which one so you know where to start looking

There are 2 sides to the equation. Positive from the battery to fuse box then lights or other accessories. The other side is grounding through the chassis back to the battery. All lights and accessories are grounded to the chassis.

As far as the horn, pull the wire from the horn then take a jumper wire from horn connection and touch to battery positive post. This will at least tell you if the horn works. Have someone push the horn button and listen to the horn relay, you should be able to hear a click in the relay when the button is pushed. This is another good place to use a multimeter. Meter between wire from horn relay going to horn and a good ground. When the button is pushed you should read over 12v on the wire.

Let us know what you find out then we can give you more ideas on where to move to next. It's a process of elimination when troubleshooting electrical problems.

[JD3426]

Hank, thanks for all the help. I have to be out of town for a while but will report back as soon as I have tried your suggestions.
Thanks again, Jim

[Hank70SS]

Wish you were a little closer, I'd be glad to help out. Don't think we have any other members close to you. Good luck, let us know what you find and maybe we can provide some help.

[JD3426]

I finally found time to dig into this again. The horn relay connections just needed cleaning, there are 12v + at the fuse box, drops to 10v when moving from one gear to another @ idle. Any ideas where to look next ?

[Hank70SS]

Where does the voltage drop occur? Does it also drop at the horn relay? How about at the junction block by the battery. If you know where it starts it makes it easier to find the problem. Could be corrosion where the the forward light harness plugs into the bulk head connector, or at the main splice near the horn relay or the horn relay or the junction block.

[JD3426]

Thanks Hank, will check tonight after work & let you know. Any chance you have replaced your horn relay ? Mine looks nothing like the ones offered at NPD or my local parts store.

[Hank70SS]

No I haven't changed mine. Disregard my previous post. I forgot this is a 72 and the wiring is different than previous years. Power for interior should come from a lead down at the starter, not off a pigtail from the positive battery cable. I don't recall exactly how it runs but hopefully you can follow it back to the bulkhead connector.

[JD3426]

Followed power across the fire wall to a spot in front of the fuse box. No drop in power anywhere under the hood that I can find. When checking the fuse box and moving the shifter it drops to just over 10v when the lights are on. I will keep looking.

[Hank70SS]

I would pull the bulkhead connectors and look for corrosion on those contacts. They plug directly into the back side of the fuse block through the firewall.