Starts then dies help

[Mmoodd]

Al I have done is fit new battery
Engine fires then dies ie won’t idle
If I keep key turned ie starter circuit engaged it revs ok then as soon as key released it dies
Cursory checks all seems ok ie fuel at in line filter near carbs nothing obviously come adrift or disconnected
Any comments ideas welcome to start my faultfinding process
Everything worked fine before battery change which may just be a coincidence

1981 tr7 convertible su carbs no modifications other than electronic ignition petronix

[seven]

Al I have done is fit new battery
Engine fires then dies ie won’t idle
If I keep key turned ie starter circuit engaged it revs ok then as soon as key released it dies
Cursory checks all seems ok ie fuel at in line filter near carbs nothing obviously come adrift or disconnected
Any comments ideas welcome to start my faultfinding process
Everything worked fine before battery change which may just be a coincidence

1981 tr7 convertible su carbs no modifications other than electronic ignition petronix

If you have a ballast resistor this could be at fault?

[Cobber]

Yeah this has a dead ballast resistor written all over it!

[seven]

Yeah this has a dead ballast resistor written all over it!

Great minds think alike Cobber

[Mmoodd]

Thanks for that
How do I locate the resistor to check it/ replace ?
Is it behind the dash

[Beans]

I'd start with a thorough check of the ignition switch.

[saabfast]

Assume the 'ballast resistor' noted is the 'eureka (resistance) wire' which drops the voltage to the coil to around 8V? The car starts on 12v from a start ignition switch contact and the drops to 8V for the 6V coil when it is released. However, I would agree with Beans to check the switch as they have a reputation for contact failure. If the 'running' contact is bad it will not put power through the eureka wire to the coil.

[Mmoodd]

Thanks for all your advice checked through and located fault to starter relay
The relay was changed a month ago for new from Rimmers inter motor part
With nothing to loose I opened up the old Lucus relay and found solder to coil adrift resoldered and it worked
Refitted old relay and she fires ok
Fault returns when new intermotor relay refitted
Rimmers sending another one
Once again thanks until the next time

[seven]

Thanks for all your advice checked through and located fault to starter relay
The relay was changed a month ago for new from Rimmers inter motor part
With nothing to loose I opened up the old Lucus relay and found solder to coil adrift resoldered and it worked
Refitted old relay and she fires ok
Fault returns when new intermotor relay refitted
Rimmers sending another one
Once again thanks until the next time

Glad to hear you got it sorted, I'd never have guess a relay

[Mmoodd]

Yea my interpretation looking at the wiring diagram tho I may be wrong is that the feed to the eureka wire is thro the relay
When the start key is engaged the start coil pulls in and then fires the starter motor
On release the normally closed contact then feeds the coil
Presume those contacts have failed