Bodywork, Paint, Interior, Trim, & Wiring

discussions about bodywork, paint, interiors, trim, audio, electrical components, wiring, etc.

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rficalora
Rob Ficalora
Cypress, TX
(2332 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

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noticed something today
Posted by: rficalora
Date: May 02, 2016 11:10PM

I can make my engine temp drop by about 4-5 degrees by turning off my headlights. Oil pressure drops slightly too when headlights are turned off too... tells me the headlights are somehow affecting reference voltage or ground.

Will have to do a little investigation to figure out exactly what's going on but thinking it has to be ground related. My headlights run through a relay and the dash switch simply provides ground to the relay switch (85 or 86, don't recall which but don't think it matters)

Other symptom is volt gauge drops from about 14v to 12v when headlights are on (engine running).


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5260 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

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Re: noticed something today
Posted by: BlownMGB-V8
Date: May 03, 2016 10:20AM

Sounds like a compromised connection in the main power circuit (including return side). Did you use 1 ga. for your main battery cables? Also the stock ground attachment to the body is inadequate. Those are the sort of places I'd look.

Jim


mstemp
Mike Stemp
Calgary, Canada
(173 posts)

Registered:
11/25/2009 07:18AM

Main British Car:
1980 MGB Rover 4.6L

Re: noticed something today
Posted by: mstemp
Date: May 03, 2016 01:06PM

Could it not be as simple as a failing regulator? When mine started to go the fan would drop me down to 12 volts. Soon as it switched off, I was back at 14.5v.


rficalora
Rob Ficalora
Cypress, TX
(2332 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: noticed something today
Posted by: rficalora
Date: May 03, 2016 08:52PM

Jim - Battery leads (positive & negative) are either 1/0 or 2/0. Both run from the battery to the engine bay - positive to the starter; negative to the stud on the frame rail near the starter. From there, I have a braided strap to the block and a few 10Ga grounds - one to the dash area where anything in the cabin gets grounded and one each goes to my headlight & fan relays. I also have a braided strap going from my trans tail shaft to the trans cross member. Net, everything is tied to the battery not relying on chassis for ground.

Mike -- Hmmmm... I don't have a voltage regulator at all. Not sure I need one with my autometer gauges, but will check.

I have two other electrical gremlins -- one might be related; other I'm pretty sure isn't.

In addition to my headlights causing volt meter to drop to about 12.5V & slightly raise both water temp & oil pressure gauges,
a) my speedo needle goes whacky sometimes. It quickly bounces up to about 60-85mph (about 2/3 of the dial sweep) & then comes back down just as fast. Sometimes it bounces around a little as it goes up & down. Only happens at idle & have only seen it done after coming to a stop (e.g., haven't seen it do it if I start the car & just idle and never any oddities when moving). I've always assumed this was a ground problem but it never annoyed me enough to chase it.

b) I have an LED wired to the +12v side of my fan relay to let me know when it comes on. But, the LED comes on sometimes when I'm driving even when the fan isn't on. I'm pretty sure this one is simply the fan spinning from air flow & generating enough electricity to backfeed & light up the LED. I've thought about adding a diode but haven't taken the time to figure out what diode specs I'd need or how to wire it up.


MGBV8
Carl Floyd
Kingsport, TN
(3168 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

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Re: noticed something today
Posted by: MGBV8
Date: May 03, 2016 09:50PM

Rob,

You are thinking stabilizer. Mike said regulator. I know you know there is one in your alternator.

If all connections are good & the belt is not too loose, then I'm with Mike. The alternator is suspect. It can't supply what you are asking of it. Possibly bad regulator or bad diode in the rectifier.


rficalora
Rob Ficalora
Cypress, TX
(2332 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

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Re: noticed something today
Posted by: rficalora
Date: May 03, 2016 10:34PM

You're right, I was thinking stabilizer.


Charles
Charles Long
McDonald, TN
(147 posts)

Registered:
09/15/2013 08:54AM

Main British Car:
1966 MGB V6 1994 Camaro 3.4L 60V6

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Re: noticed something today
Posted by: Charles
Date: May 04, 2016 09:50PM

Rob,

What wattage head lights are you running? I just upgraded to 80/100 and am seeing a slow drop in battery voltage. Me thinks it going to call for larger alternator to battery conductor. I am going to increase the wire size for grins

The bouncing gauges could be an indication off loose connection.



DiDueColpi
Fred Key
West coast - Canada
(1199 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

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Re: noticed something today
Posted by: DiDueColpi
Date: May 05, 2016 03:26AM

Hey Rob,
I'm guessing a voltage drop problem somewhere.
Your gauges work on a voltage differential. They don't really care ( within reason ) what the voltage is, they read the difference between the gauge and the sender.
So dig out your volt meter and start checking. I'd start at the battery and work my way forward. Do it with the car running and have someone turning the lights on and off. If you don't have help, wire up a flasher (hd12) to the headlight relay. And if idling for a long period is a problem. Hook up a battery charger to the alternator to mimic a running engine.
Ground and power between the engine block and the dash need to be rock solid. 0 voltage drop is ideal 0.1 would be max for good gauge operation.
Your bouncing speedo is probably a clearance problem at the sensor. If the clearance between the sensor and the reluctor is too great.
You end up with the pickup trying to read two teeth at the same time while stopped. Add in a little engine vibration and you end up with a ghost speed signal at rest. Hall sensor pickups are less likely to suffer but still do from time to time. You could also have an EMF problem but that would manifest itself at any time not just when stopped.
The LED problem very likely is the fan motor powering it up. Why not move it to the 85/86 side of the relay rather than the 30/87 terminals. No diode required.

Live like you mean it.
Fred


tr8todd
Todd Kishbach

(325 posts)

Registered:
12/04/2009 07:42AM

Main British Car:


Re: noticed something today
Posted by: tr8todd
Date: May 05, 2016 04:46PM

I thought all british cars did that.


DiDueColpi
Fred Key
West coast - Canada
(1199 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

authors avatar
Re: noticed something today
Posted by: DiDueColpi
Date: May 06, 2016 01:36AM

Happy Cinco De Mayo!

British vehicles really do have rather eccentric gauges.
But most are adjustable and can be fine tuned to any environment. Even if they shouldn't have to be!
The nice thing is that they are relatively insensitive to electrical interference.
So they end up being more accurate than you would think.
But they are British so you are constantly on edge, which is probably prudent.
So they are doing their job which is making you pay attention to the engine ,Right?

Cheers
Fred


MGBV8
Carl Floyd
Kingsport, TN
(3168 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

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Re: noticed something today
Posted by: MGBV8
Date: May 06, 2016 12:11PM

Fred sez "I'm guessing a voltage drop problem somewhere. "

Remember that clinic that Max Fulton did in the parking lot at Indy last year? He was measuring voltage drop.

[www.fluke.com]

[www.aa1car.com]


rficalora
Rob Ficalora
Cypress, TX
(2332 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: noticed something today
Posted by: rficalora
Date: May 06, 2016 11:42PM

Yeah, I remember. Not looking forward to tracking it down though. With the fuse box mounted behind the dash, there's a lot of wire back there! Verifying the drop will be easy. Finding out where/why probably won't.


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