Spitfire Starter Has a Life of Its Own
by Barry Adams, firstname.lastname@example.org Below is the problem, diagnosis and solution to a problem I asked for help from the "email@example.com" mailing list a few days ago. Hopefully, this will help someone else if they encounter this unusual problem.
Starter on 74 Spitfire turns over constantly regardless of rather the key is in the start position or not.
Reference Page 258 Haynes Workshop Manual. A WR wire runs from the starter switch to the Interlock Module (which I think is only found on the 74's). From this module a WO wire runs to post W2 on the starter relay. The above two wires should only carry current when the starter switch is in the start position. This line tested out ok.
A small gauge WR wire runs from post C1 on the starter relay to the starter solenoid. Since this is a small ga. wire I assume that the starter solenoid also has another relay in it. Like the WO wire this WR wire should only carry current when the start switch is in the start position. This line was constantly carrying current!!
Also connected to the starter relay are: A N (brown wire) connected to post C2. This wire comes from a fuse and therefore should always be hot; and a black wire connected to post W1 which goes to ground.
To verify that starter solenoid and motor were good (I'd already eliminated the starter switch, see above) I bypassed the relay with a remote starter button and everything worked.
While testing for continuity and current in the circuits I noted that the N wire and WR wire on the starter relay had been switched.
Replaced starter relay and everything works fine. I took apart the old relay and found that a set of points in it, which are controlled by an electromagnet, were fused together. Apparently, over time the reversed connection of the N and WR wires on the relay had caused this. But, I still don't understand why the car would have started normally during this period.
Hope this helps someone, someday.
I want to thank Charlie Brown, Andy Mace and Chris Pugh for holding my hand while solving this problem!
Barry H. Adams