Constant Power Circuits

Gotta love that wiring . . .
davery
Posts: 780
Joined: Sun Apr 15, 2012 8:51 pm
Your car is a: 1985 Spider
Location: Ohio

Constant Power Circuits

Postby davery » Sun Sep 24, 2017 11:07 am

I have a power leak somewhere in my 85 that I am trying to trace. It looks like there are 3 always on circuits; M, N and B. Here is what I have been able to determine.
Circuit M – Fuel Injection
Stop Light Switch
Turn Signal Switch
Hazard Switch
Seatbelt Timer
Trunk Opener Switch
Circuit N - Ignition Switch
Clock
Heater Fan Switch
Windshield Wiper/Washer Switch
Lambda Sensor Switch
Radio
Circuit B – Ignition Switch
Cigarette Lighter
Trunk Opener Relay

Does this sound right? It looks like the leak in one of these circuits.
Don Avery
Dayton, OH/Sarasota,FL
1985 Pininfarina
2011 Eos
2012 Mercedes E550 Cabriolet

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Hootch
Posts: 5
Joined: Thu Sep 07, 2017 12:28 am
Your car is a: 1978 Fiat 124 Spider 1800

Re: Constant Power Circuits

Postby Hootch » Sun Sep 24, 2017 6:45 pm

Looks like we're having similar afternoons. My turn signals/brake lights/back-up lights are wonky, and I'm trying to chase that down.

Mine's a 78, but it looks like circuit 'L' is the one that's always on. Far left, 25 amp, controlling the lighter, clock, courtesy light, hazard warning flasher and indicator, inspection lamp receptacle, remove key, fasten belt, and radio aerial motor.

Good luck!
Hootch McGee
1978 124 Spider (1592 cc motor)
2012 Mini Cooper Clubman S
2004 Aprilia Mojito
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davery
Posts: 780
Joined: Sun Apr 15, 2012 8:51 pm
Your car is a: 1985 Spider
Location: Ohio

Re: Constant Power Circuits

Postby davery » Sun Sep 24, 2017 8:39 pm

Hootch wrote:Looks like we're having similar afternoons. My turn signals/brake lights/back-up lights are wonky, and I'm trying to chase that down.

Mine's a 78, but it looks like circuit 'L' is the one that's always on. Far left, 25 amp, controlling the lighter, clock, courtesy light, hazard warning flasher and indicator, inspection lamp receptacle, remove key, fasten belt, and radio aerial motor.

Good luck!


I think my leak is one of these circuits. There appears to be no draw from any of the other circuits with the power off. I'm a little confused about fuse N. It appears from my wiring diagrams the heater fan and windshield wipers are on this always on circuit, but of course they do not work without the ignition turned on. My plan is to remove a fuse and let the car sit a couple of days. If it starts then the leak is not on that circuit.

As far as your rear lights, don't forget the grounds. I was having similar issues and it was the ground on a tail light circuit board. I rewired the grounds on the board and everything works.
Don Avery
Dayton, OH/Sarasota,FL
1985 Pininfarina
2011 Eos
2012 Mercedes E550 Cabriolet

kmoses
Posts: 353
Joined: Thu Sep 11, 2014 10:28 pm
Your car is a: 1979 Spider 2000

Re: Constant Power Circuits

Postby kmoses » Sun Sep 24, 2017 9:27 pm

Check the power draw at the electric radio antenna if it retracts when the ignition switch is turned off. Some units will not "shut off" properly when it retracts and continue to draw power.

davery
Posts: 780
Joined: Sun Apr 15, 2012 8:51 pm
Your car is a: 1985 Spider
Location: Ohio

Re: Constant Power Circuits

Postby davery » Mon Sep 25, 2017 11:35 am

kmoses wrote:Check the power draw at the electric radio antenna if it retracts when the ignition switch is turned off. Some units will not "shut off" properly when it retracts and continue to draw power.


I don't have an electric antenna, as i don't have an antenna because I don't have a radio. Which may be the issue. I removed the aftermarket radio last year, when I removed the dash, and did not install another. There was a mess of wires for the aftermarket radio and I did not remove them. t is possible there is a short in this mess of wires.
Don Avery
Dayton, OH/Sarasota,FL
1985 Pininfarina
2011 Eos
2012 Mercedes E550 Cabriolet

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baltobernie
Posts: 3314
Joined: Sun Nov 25, 2007 6:00 pm
Your car is a: 1973 Spider
Location: Highland, MD

Re: Constant Power Circuits

Postby baltobernie » Mon Sep 25, 2017 3:51 pm

Maybe Jimmy Hoffa has the reading lamp on?

The easy way to determine which circuit is drawing power unnecessarily is to use a VOM ($10 H/F one is OK). Pull each of the fuses sequentially, and place the leads of the meter across the two fuse pins. You should see a few milliamps for the circuit running the clock, but none elsewhere. Once you have isolated the offending circuit, it's a matter of finding the specific fault.

davery
Posts: 780
Joined: Sun Apr 15, 2012 8:51 pm
Your car is a: 1985 Spider
Location: Ohio

Re: Constant Power Circuits

Postby davery » Wed Oct 04, 2017 11:50 am

baltobernie wrote:Maybe Jimmy Hoffa has the reading lamp on?

The easy way to determine which circuit is drawing power unnecessarily is to use a VOM ($10 H/F one is OK). Pull each of the fuses sequentially, and place the leads of the meter across the two fuse pins. You should see a few milliamps for the circuit running the clock, but none elsewhere. Once you have isolated the offending circuit, it's a matter of finding the specific fault.


That is how I determined it was one of those three fuses. They were all drawing current. I think I have it isolated to Fuse N. I removed it for a few days and the car fired right up. This would not have happened before. Now I just need to find the short in these items.
Don Avery
Dayton, OH/Sarasota,FL
1985 Pininfarina
2011 Eos
2012 Mercedes E550 Cabriolet

ekstrandt
Posts: 87
Joined: Sat Mar 01, 2014 9:39 am
Your car is a: 1985.5 pininfarina
Location: Fayetteville, NC

Re: Constant Power Circuits

Postby ekstrandt » Fri Oct 06, 2017 8:49 am

I would suspect that o2 sensor switch. It gave my car blown fuse randomly. Disconnected mine.

davery
Posts: 780
Joined: Sun Apr 15, 2012 8:51 pm
Your car is a: 1985 Spider
Location: Ohio

Re: Constant Power Circuits

Postby davery » Fri Oct 06, 2017 11:27 am

ekstrandt wrote:I would suspect that o2 sensor switch. It gave my car blown fuse randomly. Disconnected mine.


It is possible, it is on fuse N. I will try that first. I also suspect the radio wiring. It had an aftermarket radio when I bought it. When I removed the dash the wiring looked like a rat's nest. I could not seem to determine what all these thin, little wires were for and was afraid to remove them. I bundled them all together and stuck them back under the dash. I should have spent the time and just removed the wires.
Don Avery
Dayton, OH/Sarasota,FL
1985 Pininfarina
2011 Eos
2012 Mercedes E550 Cabriolet


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