Anyone know what the AP switch does?

[Speedbird]

Having problems with an 89 carbed. Haynes manual shows "AP" switch in the engine electrical schematic. It's tied in to the coil I believe. Buddy's car quit stone dead. Diagnostics show that this switch is not fully operating right. Already changed the ignition module. That made the engine run, but only for a few minutes. Coil has been checked too. Searching for AP switch brings up all post with switch in it(500). Anyone have any ideas?

[kartracer46]

Does it crank and just not getting spark?

[zoe60]

I think the AP means atmospheric pressure switch. It's the 3rd wire going to the distributor. You can just unplug it. I don't think it is going to be the problem. It just makes the timing advance or retard or something like that when you are at high altitude. Mine's been unhooked for years. Check for 12 volts at side of coil with black/white wire. If low could be ignition switch. New Ignition module could be bad too. Check for spark at plug wires. could be something fuel related.

[Speedbird]

Does it crank and just not getting spark?

It was not getting any spark. I had an extra disty, Put it on and it cranked and ran fine.
OK-Bad module. Problem solved.
Leave car running, wash hands for supper. Engine dies.
Now it has a very weak spark and will not crank.

[Speedbird]

I think the AP means atmospheric pressure switch. It's the 3rd wire going to the distributor. You can just unplug it. I don't think it is going to be the problem. It just makes the timing advance or retard or something like that when you are at high altitude. Mine's been unhooked for years. Check for 12 volts at side of coil with black/white wire. If low could be ignition switch. New Ignition module could be bad too. Check for spark at plug wires. could be something fuel related.

We will be trying again tonight.

[kartracer46]

Check the coil for 12V, If it's not there replace the main fuse. Then if you have 12V check to be sure your ignition switch wire at the plug to see if there is 12V coming in, Then you can check the connection at the leaving with the key held in the start position to see if the switch contact is allowing current to pass to the starter. You may just have a sticky or failing ignition switch.

[boydg1]

.... If it was running and didn't blow any fuses and stopped. I would also check the battery and terminals. You could have HIGH resistance there. :pale:

[FB71]

main relay and fuse link. Sounds like excessive resistance in the power circuit to the coil.

[Speedbird]

fixed

Changed the disty again and left off the wire for the tach at the coil. Runs fine now. Seems to be a ground problem either in the wiring or in the ecu. This mostly means that the shift light doesn't work now, no big deal.