78 308 GTS - Engine won't turn off

There have been quite a few similar posts on the FChat forums with similar issues (not only the 308). I suspect during the radio installation, you have spliced (or shorted) a live battery wire to an ignition key power wire.

Hopefully all the key powered systems on the car haven't tried to run through the radio wiring. Any burning smells or super hot wiring?

 

Disconnect the radio and try it.

 

Maybe there is some relay that is kept alive by the radio, a back EMF if you will. As stated above remove the spliced wire and if all goes back to normal perhaps putting in line a proper capacity diode in the radio supply wire might solve this problem. Just a WAG.

 

Start over with the hot wire for the radio and find a different existing wire to make the connection. On my vintage Ferrari I made the connection to the cigarette lighter which is fused and always on. That way I can listen to the radio without having to turn on the ignition switch.

 

Are there any in the Owners Manual?

Sounds like a clue. I found a much later model diagram online, and the compressor clutch power seems to come directly off the ignition key. I'm still trying to figure out the blower circuit. It's the first time I've looked at a 308 wiring diagram. It's like looking for a needle in a haystack.

Maybe check behind the left hand fusebox (if the early cars have them)? That seems to have fuel pump, engine and blower fan power and lots of live wires running next to key power wires. The A, B, C fuse wiring may have issues (wild guess).

Have you updated your fusepanels?

 

Interesting. What stops when the engine stops turning? The alternator stops when the engine stops turning, but that is wired up to the battery, so I guess the phantom power source would still be there. On later Ferraris, the engine ECU(s) enable the fuel pump relay(s) when engine rpms are detected above a certain value. The 308 just needs key power as far as I can see.

Do you have an aftermarket engine management system? Also, do you have an aftermarket engine immobiliser fitted?

That's what I was hinting at in my earlier posts, but the fuel pump behaviour (EDIT) may be giving us something extra to work with.

 

Correction. Looking at the wiring diagram I have for the later 308, there is something called an airflow switch which controls power to the coil of a "start valve" relay. This "start valve" relay supplies power to the pump relay coil.

See this thread:

https://www.ferrarichat.com/forum/posts/143140742/

@Steve Magnusson if you're out there? Does airflow (induced by cranking of the engine) enable the pump?

 

He's got a carbed 308 = no "start valve" relay at all, and the fuel pump always runs with just the key "on" (if the Driver seat safety switch has been bypassed). The bottom line would be to measure the voltage at the top of fuses #1, 2, 3 = should be +12V with key "on", and 0V with key "off". If it is still +12V with the key "off", unplug the A (light blue) wire from the top of fuse #2 -- if the engine shuts off = strong sign the ignition switch is bad. If the engine doesn't shut off with the A (light blue) wire unplugged = I'd suspect something wacky with the alternator.

 

Might be a worn ignition switch. I had an airplane once that would not respond to the ignition switch, and when replaced, it solved the problem. Is there any way of testing it? Jumper it with some test cables and then disconnect each lead sequentially like the switch would do, if that is possible. Perhaps the switch can be rebuilt or repaired if it will disassemble.

 

I assume this fuse gets power directly from the ignition switch.

@jurkoj If you want to stop guessing, follow Steve's instructions... He's the guru

 

No. I was only able to find a later model diagram:

https://www.dropbox.com/t/uUU5y5YRctzcEPq5

It may help with some circuits, but, as Steve says, there are differences.

 

Exactly -- the large A (light blue) wire connects terminal 15 (+12V key "on") of the ignition switch to the top of fuse #2 (which is then bridged over to the tops of fuses #1 and #3).

Most have been bypassed by now ("jumped" to be in the always closed state). It's kind of a flaky switch design that detects the seat bottom deflection of the Driver's weight in the seat with the idea being, if the car goes upside down after a bad accident, the fuel pump shuts off even if the key is still "on". Number of people stranded when this flaky switch goes bad = many; number of people actually saved by this feature after an accident = probably zero . It's only on the later carbed US 308s, not the euro 308s.

The wiring diagram is in the back of your 150/78 OM -- you should get one (either an original or a good reprint) as some of the printed detail is quite small (especially on the schematic). This link will get you a (not great resolution) pdf scan of 150/78:
https://www.dropbox.com/scl/fi/spuk1t6hvllibxfi79uxk/MUM_308GtbGtsNorthAmerican-150_78.pdf?rlkey=p7fbhikcv5317sjyionlo4wj0&st=ooqpzsf1&dl=0

You can't contact them now (being August), but you could try MCP:
https://www.ferrariparts.co.uk
as they are the official older F part supplier, and used to have the Marparts OM reprints available at a very reasonable prices.