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MG MGB Technical - Lost some gauges and lights tonight...

Hello all,
My '79 B had some electrical items quit tonight:
*gas guage
*tach
*water temp
*turn signals
*stop lights

Clock still working, other lights OK. I checked (and moved around) the 4 fuses on the fender well. Also some connections. No difference.

Any ideas??

Thanks in advance. David
David Steverson

The common wire that all of these share is a green wire, check to see if you have an inline fuse on a green that blew, or at least check to make sure you have 12V when the car is on at the fuse terminal where the green wires push on. They are fed via white w/ brown tracer from the ignition relay on the inner fender and that gets its power from the brown when the ignition is on. If the relay is not working, make sure the white wire to the relay has 12V when the ignition is on. Hope this helps.
Jake

I had exactly this problem on my 72 GT. Everything would come back on again and sometimes run for weeks ok. The main problem was the bullet connector for the white wires in the bunch below the fuse holder. When I twiddled with it everything started working again but when I took out the connectors the whole thing disintegrated. When that was fixed I discovered that the fuse holder although appearing ok was only making good contact at the the end of its possible movement. Hence occasional fiddling seemed to correct the problem when in fact it was both things giving trouble. No further problems since cleaning the fuse holder and changing the bullet connector.

Paul
PK Flush

Similar problem: '80 LE. Corroded fuse box. R & R fixed.
R. L Carleen

Speaking of gauges, my clock does not work, nor am I able to adjust it using the set knob. Obviously the unit is NG. Rather than a clock, I'd rather have an ammeter gauge in its place. Any thoughts on this idea

cheers

Gary
gary n.hansen

Thanks to one and all for the tips. I hope to look at it this afternoon.

I almost went cross-eyed looking at that wiring diagram in the Bentley's manual, so I'm buying one of those larger color-coded ones I saw on EBay.

Dave
David Steverson

Gary - if you need an extra gauge get a voltmeter rather than an ammeter. The voltmeter gives a far clearer indication of correct running voltage and early warning of alternator low voltage and current. The ammeter can still show a small charge even when the alternator is on its way out and only just maintaining the system votage above battery voltage, only indicating a problem when the car is running on the battery. The ammeter also introduces several additional points of catastrophic failure, including wiring burn-out, and introduces undesirable resistance and voltage drops. But as John Twist says "Neither tells you much more than the ignition warning light, so buy a nice pair of driving gloves instead." To which I would add "And none of them will tell you whether your car is going to start in the morning".
Paul Hunt

David,
Be sure to compare the one you get on Ebay to the correct one for your car. I just about went batty this weekend installing a new dash harness because I was using a generic 67-70 chart. Turns out it was not correct for my car. The correct chart is #8 in Bentley and is for 68-69 cars "in certain jurisdictions". The color one I have works most of the time but the "drive you blind" one in Bentley appears to be correct for my car....there are nuances when you get into details like the color of the wire going from the stabiliser to the fuel gauge, etc. Wish I could find that one in color.

The two in-line fuses in the engine compartment go to the tail lights and to the front running lights. Gauges are also on the green circuit but aren't fused via inline fuses (at least on my 69, not sure about yours). Check the Hazard Switch that the green circuit runs through. Try operating your Hazard Switch a few times then check lights. If not, pull it out and connect the two green (plain green) wires together (bypass the switch) and see if your lights work.
J.T. Bamford

Late UK-spec cars have two in-line fuses for various green circuits plus the fusebox green circuit, under the fusebox. Late North American cars have one in-line for an additional green circuit but it only feeds the electric cooling fan. Some earlier models had inlines for the accessories circuit (70 to 73) and parking lights (67 to 69). North American cars had one for the anti-runon valve from about 73 on. The hazard switch can affect the turn (and hazard of course) signals, but not any other lights.
Paul Hunt

My problem is (apparently) the starter relay. Following Jakes posting, I had power that far, but not out to the white/brown wire.
I did a temporary jump from brown to white/brown and my blinkers worked. Hope that jump didn't hose something else....

Dave
David Steverson

Starter relay or ignition relay? Rubber bumper cars have both, and to confuse things on cars *with* a starter relay but *without* an ignition relay the wire from the starter relay to the solenoid was usually white/brown. But on cars with *both* relays the wire from the starter relay to the solenoid changed to brown/white and that from the ignition relay to the fusebox, coil and cooling fan fuse is white/brown.

The starter relay only affects cranking, it is the ignition relay that affects the turn signals and all the other ignition circuits. The starter relay is operated by a white/red wire, the ignition relay by a white wire. The other two wires on the relays are brown and black in both cases.

The relays are functionally identical even though originally the Lucas starter relay was of a rectangular design, and the subsequent ignition relay was usually round. And to complicate things even further the starter relay was of a 'short-operation' design to give low contact resistance in high-current circuits that can overheat if it is used in a 'long operation' function like an ignition, lighting, or heated back-light relay. Relays for these functions are designed to be operated for long periods without overheating. But aftermarket 40amp relays will be fine in both applications.
Paul Hunt

Paul,
Must be the ignition relay. I had already ordered a replacement from Victoria British, but I ordered the only relay I could find in the catalog, listed as a starter relay.
Either I overlooked finding an ignition relay or maybe they are the same?
I hope what I ordered is right. It would be typical for me to have gotten the wrong thing.
Dave
David Steverson

Paul, your closing line hit it right on the head. Yes it is true:

To which I would add "And none of them will tell you whether your car is going to start in the morning".

LOL, thanx

cheers,

Gary

gary n.hansen

This thread was discussed between 28/08/2004 and 02/09/2004

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