Under the Bonnet – Fall 1994

This “Under the Bonnet” is a potpourri of short topics suggested by our customers, and selected to be of interest to the novice home mechanic. 


You have just finished installing a new set of points, but can’t get the engine to start. Before allowing panic to set in, check the order of assembly at the “eye” end of the point spring. The eyelet connectors on the terminal bush and condenser leads must be installed on top of the point spring, with the upper nylon “top hat” insulating sleeve running through these. The object is to insulate the point spring and the terminal bush and condenser leads from the lower point plate, which is grounded.


The key to figuring out which wire to connect to which terminal on the coil is knowing that the wire from the ignition switch is the “hot” wire. For nega tive ground systems, this wire is positive, and should be connected to the “+” terminal. The low tension lead going to the distributor then connects to the “-” terminal. In a positive ground system, die “hot” wire is negative, and connects to the “-” terminal, with the low tension lead to the distributor being connected to the “+” terminal.

For those of us who want to look at this another way, keep in mind that when the distributor points are closed, they are grounded. Therefore the low tension lead between the distributor and the coil goes to the “-” terminal on negative ground cars, and to the “+” terminal on positive ground cars. The switch wire then goes to the other terminal.

Old style Lucas coils were marked “SW” and “CB”. These coils were almost all marked for positive ground systems, with “SW” being the switch wire terminal, and “CB” indicating “contact breaker” (points). As the newest of these coils are probably about 25 or 30 years old, I would suggest reserving their use for show, rather than daily use.


Don’t waste time looking for the ballast resistor on a late MGB or TR6 – they ate in the form of a resistive wire bound into the wiring harness. What is often thought of as a ballast resistor on electronic ignition equipped MGBs (and mis-identified as such in some older printings of our MGB catalog) is the drive resistor for the electronic ignition system.


While we publish paint color codes in many of our catalogs, many of the color codes listed are obsolete, and do not appear in current paint code listings. Where possible, we have updated the old codes to current ones, but many of them have gone away forever. In this case, if your paint shop docs not have a collection of old obsolete books, try to obtain a sample of the original paint you wish to match. One of the best places to get this is from underneath the dash.

We often get requests for the paint codes for the cars on our catalog covers. Even if we knew, the information would be meaningless because the color printed is usually very different from the actual color of the car. Colors shift from the car to the photograph, and are further changed for artistic reasons in the printing processes. Furthermore, the colors in a photo or printed image are not uniform; dark shadow areas may be printed as brown, while the highlights print as white as the paper, both on a yellow car. Obviously, then, it is impossible to say what color the car really is from the printed image.


When rebuilding a pair of anything, whether seats, carburetors, or front suspension assemblies, work on them one at a time, keeping the other one intact as a reference.


The two most important tools for working on your car arc your brain and the best workshop manual you can find (usually a reprint of the factory manual)! Even though these manuals can be fairly expensive, theit cost would pay for only an hour or so of a professional mechanic’s time; they are almost guaranteed to save you much money and frustration. Shops need good workshop manuals,

too. Can you imagine having your engine or gearbox rebuilt by someone who doesn’t know what the clearances and torque values should be? How would you feel if your newly rebuilt engine leaked oil because you made a guess at which way to install an oil slinger plate (and guessed wrongly), or simply left it out because you didn’t remember that it had to be there? Workshop manual information is essential.

Before tackling a project, study what your manual has to say about not only the particular component, but the related system as well. Figure out what parts and tools you may need for the job. Knowledge and planning are important tools. Workshop manual and brain – don’t work on your car without them.

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