Bad electrical problem

[Noel B.]

I have a 66 roadster and am having electrical issues. The car seems to run fine and then the engine just suddenly stops just like I turned off the key. It acts like the battery is disconnected - the clock and my stereo both are dead. This can happen when the car is sitting still and while driving down the road. When I get stuck I wiggle the battery cables and sometimes this seems to help. If I see the clock moving after wiggling the wires it will sometimes start. Other times the clock stops when I turn the key and I get silence. The battery is only two months old an seems to be charging while driving. I recently had my mechanic install a new starter because the solenoid was clicking sometimes. The car is a 327/300 with electronic ignition and air conditioning. Any guidance would be appreciated. I have it at my mechanics shop but haven't been able to reproduce the problem.

[John D.]

Re: Bad electrical problem

Hi Noel, Can't help you much except one thing. You say you can wiggle the battery cables. Not a good thing. John

[Noel B.]

Re: Bad electrical problem

The cables aren't obviously loose and I checked the tightness when I was stuck on the road. I just yanked on the wires because I couldn't think of anything else to do. This might have done nothing - maybe it was just luck that I was able to restart. Sometimes the engine would stop immediately after restart. Sometimes I would go maybe a quarter mile before I lost power and had to roll to the side of the road. I only had to go about two miles to get to my mechanics shop - the engine stopped three times to make it there and left me stuck in traffic. It was an adventure that I don't want to repeat.

[Leif A.]

Re: Bad electrical problem

Noel,
Sorry to hear you're having electrical issues...always a PIA. There are several (hundreds)of similar threads on this subject here on the TDB...some listed directly below. If I were to look one place first on a 50 year old Corvette, it would be the bulkhead (firewall) connectors located about six inches directly under your master cylinder. Without me going into detail, please research the numerous threads on electrical issues...you WILL find your answer. Good hunting!!

[Duke W.]

Re: Bad electrical problem

... possible defective battery. Start the car and disconnect the ground cable. The alternator should provide enough energy to maintain voltage with minimum electrical load, but you might want to increase idle speed and slip the clutch enough to no get below about 1000 starting off from a dead stop. If the problem does not occur after sufficient test time, then the battery is probably okay.

It's a good idea to rig up a voltmeter in the cockpit using extension leads to pick up voltage readings from the alternator output stud in order to monitor system voltage during the test drive.

The next step is to disconnect the cowl bulkhead connectors, carefully inspect all pins and receptacles for physical damage and corrosion. Use a magnifying glass. After correcting any problems spray them liberally with electrical contact cleaner, and when dry spray with WD-40. Let the volatile carrier dry, then reconnect.

It would be a good idea to check all connectors on the alternator, voltage regulator, and horn relay in a similar manner. Use the electrical schematic in the CSM as a guide.

The most common cause of these types of intermittent electrical problems on old cars is connectors. Coils and the ignition capacitors have also been reported as the cause.

Put together a plan and follow it. It's not that hard to do, but takes time and can be tedious. Patience and discipline is required. You could get lucky and find the problem in 15 minutes, or it may take hours.

There have been at least a couple of recent threads with similar problems, so search and read them.

Duke

[Charles C.]

Re: Bad electrical problem

I had a similar problem with my 67 B/B A/C Coupe last year. The car ran great, but occasionally while driving down my bouncy road it would just shut down like I turned off the ignition switch. Sometimes it would restart, but sometimes not. No fun to be left sitting on the side of the road.

In my case it turned out to be a problem with the ancient wires connected to the starter solenoid (that provide power to the ignition circuit). I installed short sections of new wire at the end of the OEM harness which eliminated several inches of old brittle burnt wire, as well as installed new terminals and fusible links. To date the car has not experienced that issue again. As a bonus to the repair, my battery gauge now works properly and consistently too.

I wanted to share this tidbit because you mentioned your starter was just replaced, which means the wiring at that location was recently disturbed. Might be worth a quick look at that area as well as the all the other suggestions...

Charles

[Charles C.]

Re: Bad electrical problem

Hello, I would check the ground cable where it bolts to the starter or block to verify it is getting a good ground. That may explain why wiggling the cables seemed to help, it is a loose connection at the starter not the battery. If you do separate any connectors you may want to use "dielectric grease" rather than WD40 as WD40 removes moisture but the dielectric grease is intended for ignition system use and actually seal the connections from water intrusion and protects against corrosion. I use it on ALL electrical connections including even when I replace a light bulb as it is so effective.Your problem is more or less a simple matter of isolating the cause. The post about disconnecting the battery after the engine is running was sound advice as it eliminates a bad battery causing the problem.
Good Luck,

[Charles C.]

Re: Bad electrical problem

OOPS! I may add that you disconnect the POSITIVE cable rather than the negative cable when testing for a bad battery.
Just be EXTREMELY careful you do not allow the wrench to touch any metal objects while doing so.

[Bill L.]

Re: Bad electrical problem

Noel:

(Edit / Note: Duke suggested this as well in his original answer...... so I am seconding his recommendation....)

All of the above suggestions are good to check but I would also suggest adding this: The main wiring harness for mid-years connects to the inside of the car (fuse box) at the firewall just below the driver side hood pin latch. This connection has a tendency to build up moisture, dirt and corrosion over many years and it generally collects near the bottom of the connector(s). The main power source is near the bottom and as such can get corroded. A little vibration and you get a "lights out - dead as a door nail" condition....nothing works and the car will not run.....

I had this happen on my '66 and I removed the connectors, cleaned them with a stiff bristle nylon brush and used some contact cleaner on them.... then blew them clean and dry with some some low pressure compressed air.... re-installed them ---- and no more issues..... see the photo for the location of the connectors....



Hope this helps a bit....

Regards
Bill

[William F.]

Re: Bad electrical problem

Thought main power wire was one in upper inner corner of one of the connector boxes. ??

[Bill L.]

Re: Bad electrical problem

Thought main power wire was one in upper inner corner of one of the connector boxes. ??

The '66 diagram (Doc Rebuild) that I have shows the top two wires in the connectors as circuit breakers, head lamp switch, radio & wipers etc for the AA block and head lamp doors and head lamp warning dash light for the BB block. The wires I am speaking about are the black/white (to Ameter and purple to ignition switch) at the bottom of the AA block .... those were corroded in my situation...... the black / white wire is on the bottom left (inboard) as you look at it and the purple just above it ---

In any case...corrosion / crud / moisture in either of the AA or BB blocks (on any wire) is not a good thing!!
-- and can cause an unintended short - and lights out!!!! :O)

[Rich G.]

Re: Bad electrical problem

Exact symptoms on my 66 327 350. It was the firewall connector. If you haven't yet, I'd look there first. I even changed a starter before I isolated to the connector. The tip off was very low voltage at the new starter. After re seating the connector, all is good. I guess someday I'll take it apart, but it's been good for 2 years.

Rich

[William F.]

Re: Bad electrical problem

There are many threads about how to get around bad connector in junction blocks. In ones that suggest running a jumper through firewall, always thought one of the top inner wires was the most important one and the one that needed jumping. Isn't it a red wire. If connectors are beyond cleaning, would do what a previous thread/post suggested, running a #12 wire from lower lug on headlight motor relay on driver's side kick plate to positive side of horn relay.

[Noel B.]

Re: Bad electrical problem

Thanks everyone for your quick responses. I went over to my mechanics shop and reviewed the guidance you provided with him. I have to work tomorrow but he'll work through these suggestions and hopefully we'll have a solution. I'm a fairly new Corvette owner and very much appreciate the help from this forum.

[Noel B.]

Re: Bad electrical problem

We have checked the items listed in your responses but did not find any obvious trouble spots. The bulkhead connectors looked clean and seemed tight. Of course, we can't really tell if we are fixing anything because when we let the car run in the shop it never stops. Such is the dilemma with intermittent problems. My mechanic suggested changing the key switch so I have ordered one. Any other ideas - fusible link, fuse box, coil (I have Pertronix ignition)? I'd take it for a road test but don't want to get stuck in traffic again.