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MGB 72 MGB Roadster Electrical Woes

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Deadeye

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Somewhat suddenly, my temp guage, fuel guage, tach, turn signals, and brake lights don’t work. They all worked a few weeks ago when I had the car in for its yearly safety check. Can someone help me determine the cause of these failures?

Thanks,
Chris
The mentally challenged MGB owner.
 
~hums Twilight Zone music and mutters something about Lucas~
/ubbthreads/images/graemlins/devilgrin.gif
 
First thing I would check are the fuses. If they are OK, check the connections on either side of the fuse box. Sometimes the connections need cleaning. If the fuses are OK, clean the contacts before putting them back. DO NOT use steel wool. It will catch fire if you touch both contacts at the same time. Also be a good idea to clean the wire connections at the fuse box as well.

Let us know how you solved the problem.
 
[ QUOTE ]
......... DO NOT use steel wool. It will catch fire if you touch both contacts at the same time..........

[/ QUOTE ]

I Wonders how you know that?

mark
 
/ubbthreads/images/graemlins/blush.gif KNEW someone would pick up on that, Mark!!! /ubbthreads/images/graemlins/laugh.gif /ubbthreads/images/graemlins/laugh.gif /ubbthreads/images/graemlins/laugh.gif

Good thing God looks after us, especially when we do not think about what we are doing.
 
It'll almost certainly be your #2 fuse blown (that's the one 2nd from the bottom of your fuse box with the white wire and green wire). Your fusebox will be under the bonnet (hood to you Americans) on the inner right fender.

Now, replace the glass fuse with a new glass fuse of the same amperage as was originally in there (should be a 17Amp continuous/35Amp blow rated or you could go with a 20Amp slow-blow fuse).

If it blows again, you'll need to go searching for a cause (such as a live wire shorting to ground etc.) - or take it to your friendly autoelectrician.
 
If you keep blowing that fuse, I would the the following in this order:
1- brake light switch, an easy one to check for short
2-turn signal switch, not so easy, but a likely suspect
3-Hazzard light switch, don't ask- it is just prone to fail

Good luck!

Bruce /ubbthreads/images/graemlins/cheers.gif
 
Update. All fuses are OK. After reviewing the wiring diagram, it looks like I'm supposed to be getting juice out of the white wire, while the ignition is on. I'm not. What's next?
Thanks again.
Chris
 
Trace the wire back to its source....
 
I know you said the fuses look fine and this might sound redundant – but did you actually measure voltage across them?

I only ask because I had a similar problem and it turned out to be corrosion on the fuse block terminals causing high resistance. Likewise it never hurts to actually measure the resistance across a fuse just to be sure.

If you have a volt meter turn on the ignition and measure from the terminals to ground on both sides of the fuses. If the voltage is the same then indeed your fuses are alright. However if they are more than a volt off form each other, turn off the ignition remove the fuses and recheck them with an ohm meter. The should read about 0 ohms.

Sorry if this sounds elementary just trying to help out.

Good luck,
Bret
 
Did you check the white wire for power with the key "on" in the run position...not just the "acc" position???

Stupid question I know, but we all do stupid things and no offence in intended.

If so, have someone jingle the key and see if you get any juice from the white wire while doing that...Lucas style!

Bruce
 
All I have is a simple 'light' tester, no voltmeter. I checked the white wire for juice with the car running. When tracing the wire back to the ignition, are there any connections between the fusebox and ignition that I'll have access to or just 'point A and point B?
 
Remove your centre console - the ignition switch/barrel should be obvious. Check for power at the 'hot' brown wire inputting into the ignition. Turn the key to the "acc" position - the car doesn't need to be running to check the accessory circuits! You should now also have power at the other ignition barrel terminals, with white wires attached. If not - suspect the ignition switch/barrel is faulty. To check, disconnect the battery and hook up a bypass wire between the hot brown and the white wire. Reconnect the battery. You should now have juice at the No. 2 fuse. If not, the problem lies between the ignition switch and the fusebox. Check any and all connections you can find - OUTSIDE the loom. There is an old saying, that you dn't need to cut into the loom - wires fail where they connect and at the ends - NOT in the loom (of course you could be REALLY unlucky, I guess...).

Hope this helps some.
 
Does the motor run. I am assuming so since you said the tach doesn't work. The Coil voltage comes from the same voltage (switched 12v) that comes from the ignition switch pin 3. If it does not run and the 12 volts is not present on the ignition coil or pin 3 of the ignition switch then the ignition switch must be the problem. Make sure the always 12 volts is good on pin 2 of the ignition switch before you order it. If that is gone, then make sure your connections back to the battery are good including the connection at the starter because the 12v from the battery goes to the starter connection before going up to the ignition switch.
Bob
 
check out "the mgb experience" under technical info, DIY. This site is very comprehensive yet easy to understand.
 
Thanks for the photo...if that is the flasher unit, it's some aftermarket part, it's in the wrong place, and it's obviously disconnected.

In fact, the dash loom shouldn't be in front of the console like that, especially not with unconnected terminals. Given this situation and your relative inexperience, it could be a time to visit your local mechanic, if you're wanting to get her going again without doing some homework! /ubbthreads/images/graemlins/smile.gif
 
Here's an update. Problem solved. I wiggled every connector I could get my hands on, under the dash, under the hood, and under the console. Still don't know which one was the problem but I guess it was one of the two (8 pin?) connectors behind the dash.

thanks again for the help.
Chris
 
I have exactly the same problem...intermittently !!!It happened a few times last fall, and now, this season, after a few thousand miles, problem free, it came back this week. Driving on a dry, clear day, all of a sudden, no gas gauge, tack etc...I stopped and looked at the fuses, pushed and tuggged at the wires, but nothing happened. I continued on my way with no change. I stopped for about one hour and attended to the business at hand, and started on my trip back home...approximately 30 miles. I stopped near the house to pick up a few things...when I restarted the car...everything was back to normal !!!
That was two days ago. Today, a rainey morning, I just started the car, and everything is working well !
P.S. My car is 1977 MGB
 
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