By Norman Nock
Originally published in the Austin-Healey Magazine
The following are the operating principles of the Lucas DB 10 relay #33117 as fitted to Austin-Healeys, except the late model BJ8 with double lamps.
The DBIO relay is located inside the engine compartment, bolted to the left inner fender panel. Turning the direction indicator switch on the column will allow electricity to flow to terminal #4 (left turn) or #8 (right turn). That will energize the solenoid; the magnetic field of the solenoid will attract the armature, and pulling it down sets up electrical contacts #1, #2, #3 for a left turn; #1, #6, #7 for a right turn.
Current then flows from the flasher unit through terminal #1, across the armature and to the front indicator lamp via terminal #2 or #6. The rear indicator lamp is fed via terminal #3 (or #7). This rear indicator lamp can no longer act as a stop light because the current supply from terminal #5 is broken. The other armature that has not been energized will be at rest and you will notice that the feed from the brake switch remains intact to the one stop lamp). This means that only one stopping signal can be given when the directional indicators are in use.
With both armatures at rest, the brake light circuit is via terminal #5, along connecting bridge via terminals #3 and #7 to both rear brake lamps.
Diagnosing Problems
1. Operation of the trafficator switch will cause a small click inside the relay box indicating the switch is working.
2. Locate the flasher unit and join all three BPL wires together (two wires on a BNI flasher) using a suitable connecting wire and clips. Check the #1 terminal of the relay box with a test light. This will show if electricity is available to the relay box.
3. Remove the cover of the relay box by gently prying with a screw driver at the base of the over. Caution. Some late model relay box covers cannot be removed this way and the relay box must be removed from the vehicle to remove the cover. Ground relay box to continue testing.
4. Manually operating an armature should cause electricity to be at terminals #2 & #3 or #6 & #7. If no electricity is available visual inspection of the contacts should reveal the cause. Any required adjustments should be performed with the relay removed from the vehicle. By moving the armature, you should notice that the upper contact is separated and contact is now made with the two lower contacts. Refer to diagram and align contacts as required.
Inside a DB-IO relay
Armatures normally rest against contacts at end of brake switch circuit, allowing current to flowthrough both armatures and out to rear lamps via terminals #3 and #7 when brake lamp switch is closed.
Moving trafficator switch left or right energizes appropriate armature so current flows into relay through flasher via terminal #1, activating front and rear directionals on one side only. All power to relay comes through fuse A4.
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