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MG MGB Technical - Fuse Panel Inquiry

While test driving my 72B to see if fuel economy or performance are changing I developed a new problem. My electrical system decided to act up. The Prince of Darkness has arrived.

While driving I noticed my tach, fuel gauge and temp gauge starting to malfunciton. The tach fell to 0 rpm, while the fuel and temp gauges went to the far left and proceeded to bounce against their left edges. The gauges eventually stopped bouncing and just sat with needles to the far left. I pulled over and realized my turn signals didn't work and my break lights were out.

Since car seemed to be running fine, and their was no noticeable smell of burning wiring I headed back home.

Looking over vehicle I could find nothing wrong until I noticed the the 3rd fuse down from top(30A)on a 4 fuse panel was burned out. I found a 20A to replace it to see what would happen. Everything came back on.

I headed to the autoparts store to buy 30A fuses, only to have the 20A blown by the time I rounded the first corner. I bought fuses and drove home.

I started looking for bare wires (of which there are plenty behind the center counsel as the lighter, radio and light are not connected since my recent purchase. I found no wire problems and replaced fuse again. Everything again came on.

All has been fine up to now. I can think of nothing I've done to change anything electrically. I must add that I am not sure if the turn signals were included in the blown fuse problem, but brake lights are for sure.

So I have three main questions:
1. Is the 4 fuse panel proper for this vehicle?
2. Is it normal to so many unrelated things on one fuse (tach, fuel gauge, temp gauge, break lights)?
3. Any immediate thoughts for a source for fuses blowing?

My heater fan quit at this time too, but I think that is unrelated to the fuse problem, as the wire going inside the motor did respond to wiggling, for awhile.

Again, all your responses are Very Much Appreciated. Who knows in a year or so I may offer advise.

BobA
Stillwater, MN
R.W Anderson

1. Yes the 4 fuse panel is correct.
2. Yes, with only four fuses there are a lot of things on the same fuse.
3. Not one particular item, there are so many to chose from. I suggest checking the wiring diagram and see what items are on the fuse in question, then carefully inspect the wiring to each one or unplug it if it is easy to do and try again with a new fuse. As fuses can get expensive doing this type of troubleshooting, I usually buy an automatic resetting circuit breaker of the correct rating and use that until I have the problem isolated. They run around $6, but usually pay for themselves in fuse savings quickly.
Poor connections are a leading cause of intermittant electrical problems such as the wipers. Clean all contacts you can and I advise cleaning and soldering the rear of the fuse block contacts. They tend to loosen around the rivits and cause problems.
Bill Young

Bob - You've located probably THE most important fuse in your car - unfortunately, many circuits (as you've found) are wired through it, making troubleshooting troublesome.

First, a 30 Ampere fuse is a little bit large for this application. An "American" 20 amp fast-blo (plain filament) fuse is much closer to the one you need. It's very likely that you have a Green wire somewhere that's intermittently touching ground. The trick is to find out where. Ypu'll need to look for places that the wires go over sharp edges of bodywork, or where they may have been pinched by other components. In the midgets, the right side footwell "kickpanel" is a good place to start, as this is where the wires split to go to the back of the car. In an MGB, your mileage may vary <grin>.

You can disconnect some of the green wires coming from the fuse block to help isolate the problem (divide and conquer), but driving without signals and/or brake lights is not very advisable. That's what make intermittents so much fun to find. The only good recompense is that they're very satisfying when you finally DO find them!

I had an old mentor who advised against ever even trying to fix intermittent problems (obviously not an option for you). He said, "With an intermittent problem, there's only three things that can happen: It can get worse, which makes it easier to find; It can get better, in which case you don't have to fix it at all; Or, it can stay the same. Now, if it stays the same, there's only three things that can happen....."

Best of luck - - Alec
Alec Darnall

Wiring diagrams are available at http://www.advanceautowire.com

Make youself a couple of enlarged copies, one for reference and one to make notes on as you check the circuit. While checking the circuit, inspect and clean each connector and use dielectric grease.

When I had a problem with the green circuit, it seemed like the fuse would imediately blow. After I found the short, it became clear as to why it would blow. My problem was a pinched wire going to the brake lights after the brake light switch. Every time I went to start the car, I would put my foot on the brake pedal. The wire had been pinched during a repair a year earlier and took awhile for the insulation to wear through.

Connectors are available at the usual suppliers,
Victoria British
Moss Motors (find a local distributer, this may save you on shipping and you will most likely get someone with experience working on cars.)
britishwiring.com (they charge less for shipping on small orders than the other two.)
Kimberly

Bob - I had EXACTLY this sypmtom on my MGB last summer. It turned out to be the green wire that connects to the gearbox switch that operates the "fasten seat belts" light and buzzer. I had long ago disconnected the buzzer, so did not realize that the gearbox connection was undone. The green wire would dangle down beside the gearbox, and would swing side to side, and ground out against the gearbox, causing many fuses to be blown, and the guages and the signals to stop working. This happened when I rounded a corner at enough speed to swing the wire against the gearbox. The rubber cover over the terminal at the end of the wire had actually worn itself down, likely from years of rubbing against the gearbox!
Since your symptoms seem related to rounding corners, the first thing I'd do if I were you is put the car on jack stands and climb under to look for the connections to the gearbox.

Cheers,

Erick
Erick Vesterback

Hi Bob,
I believe your car has an ignition relay (located close to fuse panel) original was a round type. If so, then I believe your trouble may be that. You can replace it with any 30amp 4 connection relay, paid $5.99 for the Bosch one I used.
Cheers'Ric
R.A Willis

If you haven't replaced the entire wiring harness just skip 150 hours of future aggravation and go ahead and do it. Most of us that have done it don't spend any more time doing electrical stuff. After the aforementioned 150 hours or so I haven't touched electrical once in two years. It's a wonderful feeling and allows you to do other things and much safer...not leaving you at roadside some night. It's these kind of aggravating test, test , trace, trace problems that eat up time. I've rebuilt whole sections of the harness to cure problems and it's simply age not a problem with design or inherent quality.

Might sound like taking a cannon to a squirrel problem but believe that you won't regret it. British Wiring in Chicago area is great..little more expensive but worth it and VERY knowledgeable. Oh...and put in a battery cutoff switch behind the passenger seat to save many headaches and provide additional theft protection
J.T. Bamford

Bob,

Is the heater is on that fuse? If so, I'd start with fixing the problem existing there and see if a new fuse lasts. If so, good. If not then plenty of good advice above.

Regards
Roger
Roger T

Fuse Panel - Electrical Problem Update

After doing a lot of wire tracing and disconnecting wires from fuse panel I've learned the following, but still have a problem.

First I have ordered the circuit breaker style fuses (20A & 30A - $6 ea. @ NAPA). Upon cooling they re-set themselves. Yes, at $6 I could have bought a lot of fuses (10), but I've gone through 5 fuses so far.

If my 3rd fuse from top blows the following items do not work: temp gauge, gas gauge, tach, backup lights, brake lights and turn signals. I think my heater fan is a separate problem.

By replacing fuse the gauges and break lights would come on. I didn't know the turn signals weren't working, so this problem may have been there all along. I also didn't know the backup lights had stopped working.

With car setting still fuse doesn't blow. So with gauges and brake lights working I started looking at turn signal wires & contacts as well as back up lights.

This got me to removing the steering column cover because the turn signals came on by chance when I was playing with signal lever and touching ignition key on&off. So I used elec. cleaner on signal assembly and turn signals came on. Upon further checking the back up lights came on. So I used elec contact cleaner on ignition too.

So here we are with everything working, various bare spots on wires covered with elec. tape, various loose connections with new ends on them and secure, and engine running & me - I'm turning things on and off, on and off trying to blow a fuse. All appears fine - but I don't know why. So what next - another test drive!

After going around one block and after another and hitting as many holes in the road as I can, nothing - everything still works. But then Prince Lucas must have seen my confidence rising, so the fuse blew while just driving along.

I'm letting it set for now until circuit breaker fuses come in on Tuesday.

Any more ideas!!!! Does anyone make sense of this and see it pointing to a likely suspect? I think I'm back to the drawing board. I'm wondering if spraying the turnsignal lever assembly and ignition are really associated with all this.

Thanks again for any assistance. Other than that the car is running fine. Probably getting better gas mileage now too, with the alternator not having to produce as much energy with half the electrical system in blown phase!
R.W Anderson

R.W Anderson-

30A is too much and will not provide the correct protection for the circuit.

The original fuses are 17/35A. Any continuos load over 17A would cause the fuse to blow or a spike over 35A would cause the fuse to blow.

I see the advantage of using the circuit breakers for trouble shooting, but I wouldn't want to use them all the time due to the fact they would just cover up the fault and allow the wiring to burn up more than a fuse would.

Four years ago I spent a weekend with a wiring diagram going over the wiring in my car, cleaning, or replacing, most of the connectors. I used dielectric grease on all the connections I serviced to prevent future corrosion. I also replaced a couple of wires where the insulation was brittle. I haven't had any trouble since then and I spent less than $20-. It was less work than replacing the harness.

Connectors and wire are available from many sources. I like britishwiring.com because their shipping charges are lower than Moss or Victoria British.

-Kimberly
Kimberly

This thread was discussed between 15/09/2006 and 18/09/2006

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