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Electrical trouble
Posted by: LesH ()
Date: August 02, 2018 01:03PM

'65 Corsa 140/4 convertible.

No taillights, brake lights, dash, or interior lights (all the same fuse). Fuse blows instantly when installed (key off, car not running).

So I figured it has to be a circuit that normally has power with key off - interior lights or glovebox.

Looks like the left hand interior light (under dash, on a coupe/sedan this would be the dome light circuit) has power on the ground wire.

Circuit goes through headlight switch so I removed/unplugged the headlight switch (my arm has almost healed already). No change so it's not that switch.

Any hints before I start removing the instrument panel and accessing the wiring harness back there?

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Re: Electrical trouble
Posted by: TerribleTed ()
Date: August 02, 2018 01:25PM

You have a direct short to ground somewhere. I would start with the easiest thing. Remove the light bulbs in the circuit one at a time and check to see if one of them is causing the short. After that you pretty much have to go step by step thru the wiring from the fuse box out to find where there is a direct connection to ground from power.

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Avid Corvair hobbiest since 1984.
I have personally performed ground up restoration on over 20 Corvairs.
I currently work full time at restoring and repairing Corvairs.
Located in the Atlanta Georgia area.
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Re: Electrical trouble
Posted by: MattNall ()
Date: August 02, 2018 01:28PM

Lee.....most likely in the rear...

Unplug rear taillight sockets. then license plate light for starters.





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Electrical trouble
Posted by: moomba32 ()
Date: August 02, 2018 01:44PM

No taillights, brake lights, dash, or interior lights

Taillights wouldn't be a problem until after the switch is pulled so shouldn't be those, same with dash lights plus he unplugged the switch.
That leaves the brake lights, interior lights and circuit to light switch.
Can unplug brake light switch to eliminate, those.
I'm betting it's interior lights.
Seeing as it blows instantly it's a pretty firm ground/short, rig you up a light, 12V with two wires wrapped around the ends of a blown fuse and reinstall that fuse, the light should burn until you find the problem, now wiggle wires everywhere and what for your light to flicker.
Good luck.

Don Marlowe
66 Monza 2Dr 140/pg
64 Spyder convertible now, 110/pg
Eutawville SC

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Re: Electrical trouble
Posted by: Murphy ()
Date: August 03, 2018 05:50AM

Check the wire that feeds the dome light. In two different cars I found the wire going to the dome light inside of the left "A" pillar had all the insulation chewed off by Rodents. It was an area about two inches long, certainly enough to short it out.

Of course, they could have chewed anywhere.

65 Monza Coupe
61 500 Coupe (under Construction) Getting REALclose.

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Re: Electrical trouble
Posted by: Lane66m ()
Date: August 03, 2018 06:07AM

Pull dome light bulb. Then put another fuse in. That eliminates wires from bulb to switches.

Open up tunnel panel and check in there for chafed wires. Also check connector in engine compartment. Make a jumper to connect red wire pins together without putting connector together. That will split front from rear. Then put a fuse in.

Al Lane
Ellabell GA

1966 Monza Coupe, 110 hp, 4 Spd
1968 Camaro SS Coupe 350 CI 295+ HP PG
1964 Greenbrier Deluxe, 6 dr, 80 hp car engine, PG
2015 Chevrolet Malibu 2LT
2018 Chevrolet Silverado LTZ Z71 Centennial Edition
1947 Farmall A tractor 15 hp


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Re: Electrical trouble
Posted by: BobV66Vair ()
Date: August 03, 2018 06:40AM

Has any other work been done to the car recently? Maybe something got pinched during other work? Rodents would be the alternate answer. Follow some of the other tips for testing for shorts in the constantly powered systems.

Bob Vinnacombe
Sandy, Oregon
1965 Corsa 140 stock
1966 Monza Soon to be race car
1968 Monza Parts for now

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Re: Electrical trouble
Posted by: joelsplace ()
Date: August 03, 2018 08:19AM

"Pull dome light bulb. Then put another fuse in. That eliminates wires from bulb to switches."
No, that only eliminates the bulb.

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Re: Electrical trouble
Posted by: LesH ()
Date: August 03, 2018 09:56AM

Thanks guys for the hints. More troubleshooting this weekend.

Convert - so no dome light.

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Re: Electrical trouble
Posted by: Frank DuVal ()
Date: August 03, 2018 11:20AM

Dome lights and courtesy lamps under dash all have HOT wires going to them. This is typically an orange wire. Always hot. Should be, not a symptom of something wrong.

Door switches and CCW switch on headlamp knob GROUND the lamp circuit to make the dome and courtesy lamps light.

Courtesy lamps have insulated sockets, so there is no "ground" terminal of that bulb until a switch closes, so hot on the bulb shell is OK! Since bulb shell of the socket IS NOT grounded, but goes through the harness.

Frank DuVal

Fredericksburg, VA

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Re: Electrical trouble
Posted by: Lane66m ()
Date: August 03, 2018 12:18PM

So pulling the bulb only tells you if one side of the wire is good.

Al Lane
Ellabell GA

1966 Monza Coupe, 110 hp, 4 Spd
1968 Camaro SS Coupe 350 CI 295+ HP PG
1964 Greenbrier Deluxe, 6 dr, 80 hp car engine, PG
2015 Chevrolet Malibu 2LT
2018 Chevrolet Silverado LTZ Z71 Centennial Edition
1947 Farmall A tractor 15 hp


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Re: Electrical trouble
Posted by: MattNall ()
Date: August 03, 2018 12:31PM

Actually tells you nothing until you use a DVM and check for 12 v + on the orange.... and test continuity to ground on the white, as you open / close doors and turn the rheostat





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Electrical trouble
Posted by: Tom Z ()
Date: August 03, 2018 12:49PM

I've taken many '65 wiring harnesses apart, only way for me to learn! A diagram and a volt meter are all I needed

Tom Z,,Rochester NY

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Re: Electrical trouble
Posted by: LesH ()
Date: August 03, 2018 01:03PM

when I pull the bulbs, there is power on the ground side of the driver's side lamp - I don't think there should be any power there

Frank DuVal Wrote:
-------------------------------------------------------
> Dome lights and courtesy lamps under dash all have
> HOT wires going to them. This is typically an
> orange wire. Always hot. Should be, not a symptom
> of something wrong.
>
> Door switches and CCW switch on headlamp knob
> GROUND the lamp circuit to make the dome and
> courtesy lamps light.
>
> Courtesy lamps have insulated sockets, so there is
> no "ground" terminal of that bulb until a switch
> closes, so hot on the bulb shell is OK! Since bulb
> shell of the socket IS NOT grounded, but goes
> through the harness.

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Re: Electrical trouble
Posted by: Frank DuVal ()
Date: August 03, 2018 08:57PM

Les, what do you mean by "ground side"? The shell of the bulb or the white wire?

The shell of the bulb can be hot, as the shell of the socket does not internally connect to the screw holding the socket to the dash.

Also, with the dome lamps off, both sides if the bulb can be hot, as nothing in the circuit is grounded (attached back to the negative terminal of the battery) so the white wire of one courtesy lamp socket will read to +12 volts through the other courtesy lamp! With both bulbs out (and the dome if a hardtop vehicle with all three "dome" lamps) then only one terminal of the socket should read back to +12 volts.

With the door open (dome lamps lit if installed) then one terminal of the courtesy lamp will read +12 and the other terminal should be ground. It does not matter to the bulb which terminal is hot and which is ground.

Frank DuVal

Fredericksburg, VA

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Re: Electrical trouble
Posted by: LesH ()
Date: August 04, 2018 08:21AM

The white wire, driver's side, is hot. Both door switches are removed, both bulbs removed, sockets removed from holders and hanging loose.

Back to garage shortly.

Frank DuVal Wrote:
-------------------------------------------------------
> Les, what do you mean by "ground side"? The shell
> of the bulb or the white wire?

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Re: Electrical trouble
Posted by: joelsplace ()
Date: August 04, 2018 08:58AM

Sounds like the driver's side socket may have a short.

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Re: Electrical trouble
Posted by: Frank DuVal ()
Date: August 04, 2018 09:36AM

No, sounds normal if there is still one bulb in the dome lamp circuit.

Do you have one dome lamp, typical hardtop, or two courtesy lamps, typical convertible, or three lamps, an option on hardtops with a dome lamp and two courtesy lamps.

And do you suspect a prior owner did other lamp modifications?

Frank DuVal

Fredericksburg, VA

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Re: Electrical trouble
Posted by: joelsplace ()
Date: August 04, 2018 10:43AM

Convertible. No dome light.

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Re: Electrical trouble
Posted by: LesH ()
Date: August 04, 2018 01:31PM

Thanks, you pointed me in the right direction.

The behavior I was seeing in convert. courtesy lights was normal (hot on the ground on one side) because I had the bulb installed on the other side.

Removed that bulb and everything looked good... slowly put it back together (I was as far in as having the headlight switch in my hand) while checking from the fuse to ground... circuit stayed open to ground until I activated a switch somewhere.

So it is all back together and working now.

But I have no idea what the actual problem was... I expect it to come back.


Frank DuVal Wrote:
-------------------------------------------------------
> No, sounds normal if there is still one bulb in
> the dome lamp circuit.

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