Can anybody confirm what this relay does in a 408, please?

[PEU186F]

Conventional uk practise amongst better class cars of the period, including Bristols, was to use a ballast resistor in series with the primary circuit of the coil. So the coil was normally running at less than 12 volts. The ballast relay was short circuited by the ballast relay when the starter solenoid was activated to deliver all volts available in the interests of a bigger and better spark to get the lump turning over. I say all volts available as starter motors of the period placed a tremendous load on the battery and the cabling to the starter, resulting in a significant voltage drop to the coil whilst the starter motor is activated. (If you look carefully at your Bristol you will note that the main feed to all circuits from the battery is actually wired off the starter solenoid - why they did that the lord only knows)

The ballast relay is indeed the tan ceramic looking block that John Simmons points out.

Not that this applies to Bristols but I noted a Chrysler maintenance film on Utube not that many months ago that indicated that Chrysler practise was to have a ballast resistor in series with the coil at all times, so no ballast resistor or relay. This in the interests of reducing arcing across the points and prolonging point life. I don’t claim to understand the principles involved, but there’s another reason for having one, for those who stick with points.

Another plus for a ballast resistor is that if running on points the coil is much less likely to overheat if you inadvertently leave the ignition on whilst the engine isn’t running. I have noticed that the 410s coil barely gets warm in this circumstance whilst the Morris van’s (a great fun car, but not one that one could call better class) gets quite uncomfortable to touch.

I can’t actually swear that the original regulator box for the dynamo on a 408 was fitted above the fuse box but that’s where the alternator control box was fitted by Bristols on the 410 so it seems more than likely.

Roger