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MG MGB Technical - MGB Dying Out

My 1978 MGB dies out as soon as I move the shifter to the left of 1st and 3rd but not yet placed in reverse (down). The tach immediately drops to zero and the car dies when I do this. The car idles just fine and I can engage it in other gears but dies out once placed in the other gears too. This happens whether cold or at normal operating temperature. Even after the car dies out, I still have current and does restart right away. Any help would be appreciated for this unusual problem.
Joe

Joe,
Your car has the overdrive switch in the top of the gear shift lever - right? I bet the wires that run down the lever to the switch in the gearbox are worn through and shorting. You should unscrew the gaiter around the lever and lift it up so you can inspect the wiring. This damage to the cables is very common and needs to be fixed before you start blowing fuses or worse.
Mike
Mike Howlett

I would think that the reverse light switch might be somehow involved. It could be shorting out the ignition thorugh some round about way.

Electrical problems are always such fun on the MGB. I have found many odd problems over the years with them.

Good Luck
John in Music City
John Lifsey

No overdrive, but I'll check the reverse light wiring. Maybe by removing the center console and re-installing it, I might have disturbed something. I'll keep everyone informed of my progress since this may be useful to others upon resolution.

Cheers.
Joe

A problem with the reverse light circuit *should* blow the fuse if anything, and won't stop the engine. The exception is if there is a bad connection at the ignition relay and instead of the green fuse blowing the bad connection at the relay is acting like a self-repairing circuit breaker which *will* affect the engine and everything else off the relay. If the overdrive wiring is at fault this is unfused and will normally cook the loom, but a bad connection as above will do the same thing.

Measure the voltage at the green and brown/white wires on the fusebox and see if the 12v drops right down on either or both as the lever is pushed across. If on both do the same at the brown/white and brown wires at the relay. Some where along the way you should find a point where the voltage drops and one where it doesn't, the problem lies between the two. Check the spades *and* the wire connectors that are on them.
Paul Hunt

Mike, the "or worse" on that one is correct. The overdrive circuit is unfused and this "feature" once caused me to let all of the smoke out of my electrical system at once :-(
Rewired engine bay and inexpensive in-line fuse holder to fix. Permanently.
Tim Cuthill

Very easy to retro-fit a fuse to the OD, get an inline and solder two bullets to its tails, and an extra single connector. For cars with the manual switch on the dash or column locate where the yellow wire in the main loom joins the yellow/red in the gearbox loom at the mass of connectors where the firewall joins the right-hand inner wing. You can put another one in the white between the main loom and the rear loom to protect the fuel pump circuit, this is another cause of loom damage. For cars with the manual switch on the gear lever you are looking for a double connector where a white/brown from the main loom feeds a white to the fuel pump in the rear loom and another white/brown in the gearbox loom. Here you can either use one fuse for both circuits or have one fuse for each as you prefer. All are easily accessible and in a relativey 'clean' area of the engine compartment, and easily removable if one should wish.
Paul Hunt

Somehow this thread got off track. As stated above, the car does not have overdrive, and never did. I will try Paul Hunt's suggestion this weekend and send another thread on the outcome. Thanks to all for your suggestions.
Joe

Funny the tangents that we go off on, here is another, try starting it in reverse with clutch in, and move the gear stick to neutral
Tatty

Joe. All of the late model, NA spec, gearboxes had the "overdrive" lock out switch on them. It was used for part of the emissions control equipment on cars not equipped with OD and for the emissions control and OD on cars with overdrive. The statement "the tach immediately drops to zero and the car dies..." tends to indicate some form of low tension circuit problem. Running a jumper wire from the white wire fuse box connection, back into the cockpit, then hooking up a volt meter to the wire and a ground would allow you to see if the current is dying when you operate the shifter and/or clutch. Les
Les Bengtson

Yet another tangent - Haynes shows *two* gearbox switches for late model NA cars, the second being a microswitch controlling the TCSA *in series* with the OD switch (4th only by this time). This is definitely wrong, but there is a possibility that 1980 gearboxes did have a seperate microswitch controlling the TCSA independantly to the OD switch, which would only make sense if OD was put back to being on 3rd and 4th again. Hopefully I will get chapter and verse from a 1981-issue workshop manual soon.
Paul Hunt

This thread was discussed between 06/01/2003 and 11/01/2003

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