1968 Cutlass Convertible. Switching from carb to fuel injection. There is a 30 amp inline fuse between the positive terminal on the battery and the horn relay (blue wire), but I don't see that in the wiring diagram. Is that supposed to be there?

 

Correction. On a 1968 there is no fuse in the wire from the battery to the horn relay. There is normally a fusible link between the horn relay and the firewall connector. I'm guessing that a prior owner installed the 30A fuse. Note that the wire from battery to horn relay is supposed to be 10 gauge.

 

Thanks for the quick reply. Is 30 amp enough?

 

See my update. Fuse and wire sizing will depend on the electrical load you are adding. 30A is probably enough to get the car started, assuming all other loads are not connected with the key in the START position. 30A is also the limit for that 10 gauge wire. This is why GM used isolation relays on high current loads like power windows and seats that only allow those items to work in the RUN position (presumably with the engine running and the alternator charging).

 

There really is no reason to even have a fuse there. The only thing that wire does normally is charge the battery. If in case of an alternator output failure, then the battery would power the car.

 

The only electrical change made was the change from carb to Holley Sniper, which required an electric fuel pump. That added a red wire from the battery, but that wire doesn't go to the horn relay. Everythinig was fine over the past year, but yesterday the fuse blew twice. I noticed that my voltage guage pegged above 14 volts, so I replaced the voltage regulator to see if the old one bit the dust. The new regulator is only putting out aroind 10 volts. I aked about adjusting it on a seperate post.

 

Actually that wire powers the car when starting, before the alternator is charging. Granted that's normally a very short period of time, but it does power the rest of the car.

 

It only charges the battery? When that fuse blows the car dies - engine and everything.

 

Then your alternator either isn't charging or isn't wired properly. Once the car is running you should be able to pull that fuse and the car should still run.

 

I'll add that clearly your car has had someone mucking with the wiring. Without photos, we're only guessing as to what's been done to it.

 

Following.
I'd test your alternator firstly. Should be delivering >14.0VDC at battery car running - never over 15.0VDC - somewhere between 14.3VDC - 14.7VDC.

 

Sounds like it.

 

Should that wire go to the positive or negative terminal on the battery?

 

So, think about this just for a second. A fuse (or in-line fusible link) is never placed on the negative (ground) side of ANY wiring. Not trying to be a smart a$$ but POWER is fused, ground is not fused.

 

I meant with the engine running.

x2 if the fuse is connected the way you described and not the wire from the horn relay to the bulkhead connector.

On a side note, unless a car is positive ground.

Here is a wiring diagram:

 

...you got me...

 

Looked at the wiring and compared to wiring diagram and everything looks ok. So, will check alternator (which is practically new) and votage regulator

 

Thanks, better than the black and white diagram I have.

 

Phil,
Welcome to CO dot com.
New means suspect nowadays...especially if the country of origin is from our favorite country known for the highest quality of inferior parts guaranteed to last at least two mmm maybe 3 days.

Full disclosure, anti-plagiarism, I forget where this came from it is not entirely mine. I've made some tweaks and have used it for years troubleshooting externally regulated charging systems.

Alternator/ regulator testing:

Check for battery voltage at the stud where the large red or orange wire connects to the alternator. You should have battery volts. If not, repair the wire or circuit.

Disconnect the plugs from the regulator and alternator.

Check the continuity of the blue (field) and the white (relay) wires between the plugs. Repair any wire that does not have continuity.

Reinstall the alternator plug and leave the regulator plug disconnected.

With a voltmeter, check the voltage at the number 3 terminal on the regulator connector, it should read battery voltage. There should not be any voltage at the other three terminals at this time.

If you have voltage at the number 2 terminal, R on the alternator, you have a leaky diode in the alternator, replace the alternator. This will cause a battery drain and the regulator will be hot to the touch with the key off.

Now turn the key "on", you should have voltage at the number 4 terminal, this wire comes from the fuse panel. If you had an “idiot light”, this would be from the bulb.

This is what is called the exciter circuit, without voltage to this terminal the charging system will not begin to charge.

If no faults have been found so far, leave the regulator plug disconnected, make sure all wires are clear of the fan, and start the engine.

With a voltmeter connected to the battery and the RPM at approximately 1000-1200, jump from the F terminal of the regulator plug to the 3 (orange or red wire) terminal.

You should see an increase in voltage at the battery and hear the alternator working. If you hear a growling noise from the alternator you have either a bad diode or a bad stator winding.

Don’t leave the jumper connected too long because you don’t want the voltage to go over 15 volts for an extended period of time.

If you don’t see the voltage go above battery voltage after a few seconds then you have a bad alternator.

If the voltage rose quickly and then decreased this means you have a slipping fan belt.

Now connect a voltmeter to the number ‘2’ terminal (white wire) of the regulator connector and again momentarily jump from ‘F’ to 3. You should see about 8-10 volts.

If not, you have a bad diode in the alternator.

If all is OK up to this point reconnect the regulator connector.

If it is still not charging, run a separate ground wire from a good ground to the base of the regulator. If still not charging, replace the regulator.

If you have an overcharging condition, it is either a bad ground at the regulator base or a bad regulator.



Look into the new solid-state regulators. You can install a vintage Delco lid on these new regs and nobody will know.
Note: I always recommend rebuilding the stock original parts. Never turn in old-school USA parts for the core charge.
Steve

 

Thanks, great info

 

If you don't have the ability to download the wiring diagram Eric provided, you can find it in the Electrical forum:

1968 A body wiring diagram

I'd suggest you buy an original OEM (used paperback) 1968 Oldsmobile Chassis Service Manual (CSM) which contains the color wiring diagram in addition to all the pertinent information pertaining to your vehicle.

Good Luck.