Audi 90 7A won't start unless battery is disconnected and then re-connected

[T Bo]

Hi again, Tom here from South Australia (T Bo), I posted in the Introductions area first time yesterday. My project is a 1989 Audi 90 Quattro 7A. It's coming along OK, slowly of course. The car starts and runs quite well, although it will only start if I disconnect the battery (and then re-connect it of course). Have to do this every time I want to start it. The car is completely stock. I assume something is re-setting ? Anyone got any ideas ?

[Lago Blue]

Hi Tom,

Welcome sir. When it doesn't start, what do you not have, rotation, spark or fuel?

[T Bo]

It certainly turns over. Will have to check and get back to you about fuel and spark. I find it very odd that all is OK after removing and reconnecting the battery lead.

[Ian Simmonds]

Is there something hooky going on with an old after market alarm? My old GT went through a spell of randomly cutting out at the most in opportune times like powering up a motorway slip road then almost immediately restart. It’d wait 4 or 5 months then do it again. I lived in terror of it. Turned out to be a redundant alarm system.

[Mikes2]

My 7A has a small attachment on the + battery terminal - it's a short loom with a fuse. If it's not fitted, the car will not start.