66 coupe - need help w/ electrical problem

[Dale S.]

Re: 66 coupe - need help w/ electrical problem

Remember, All rebuilt alternators are not equal, I have sold many brands, from Kimco in the early 1960 to Clutch exchange, Delco, Metro and many other brands. Some were good, some started out good and some were never any good. John Pirkle has been in business for a long time for a reason. Did you store test your rebuilt alternator before it left the store? We always did. Dale

[Bill F.]

Re: 66 coupe - need help w/ electrical problem

Dale,
I purchased the alternator (came in a AC Delco box, M-2907, D-08-09) from Zip Corvette Products in VA, so no, it was not tested in my presence. I am planning to take it to a local auto electric shop this week to be tested.

Since my last post I have stripped most of the cover off the wiring harness from the alternator to the firewall plug, and from the starter to the other firewall plug:
1.
2.
3.

Also checked the back of the battery gauge - the wires there look OK, don't look like they got hot.

Anyone replaced their engine harness recently? Any pointers? Recommendations on who to buy the harness from?

Thanks for all the help so far!

[Thomas P.]

Re: 66 coupe - need help w/ electrical problem

My suggestion is to very carefully check the connections and wire that runs between the starter solenoid "B" terminal and the horn relay center terminal -- in my 1964 shop manual, it is marked as "12R."
Make sure all terminals and the wire have good connections.

The reason I say to check this wire is because the ammeter is "shunted" across this wire -- if that wire or connections fail, for any reason, all current (except starter current) will flow directly through the ammeter and the small wiring to the ammeter, which will cause it to burn up.
The ammeter should normally see only a small percentage of the current.
But, if that "12R" wire I mention has a poor connection much more current flows through the ammeter.
To prove my point, disconnect the ammeter at the ammeter terminals and tape them off -- this way, no current will flow through the "shunt" ammeter. The vehicle should still function normally, except the ammeter will not register anything.

Keep in mind: a shunt ammeter only measures a small amount of the actual current (but is calibrated to read as though it sees all the current) -- if the shunted wire becomes an open circuit, all of the currrent goes through the ammeter and wire to the ammeter, which it should normally never see.

Edit:
John Hinckley, in his post above, is saying you have a 10 guage red wire.
My '64 shop manual is stating "12R" which tells me that my '64 has a 12 guage red wire and you probably have a 10 guage red wire.
I think my alternator is 36 amp and yours is higher, so you probably have a heavier guage wire -- most likely marked "10R."

[Bill F.]

Re: 66 coupe - need help w/ electrical problem

Will check, thanks.

[John H.]

Re: 66 coupe - need help w/ electrical problem

Edit:
John Hinckley, in his post above, is saying you have a 10 guage red wire.
My '64 shop manual is stating "12R" which tells me that my '64 has a 12 guage red wire and you probably have a 10 guage red wire.
I think my alternator is 36 amp and yours is higher, so you probably have a heavier guage wire -- most likely marked "10R."

Tom -

Bill's car is a '66 (10-ga. main feed), not a '64; the '64 used a 12-ga. main feed.

[Thomas P.]

Re: 66 coupe - need help w/ electrical problem

Read this:
--------------------------------------------------------------------
An ammeter is used in series to measure the current flow in a particular
circuit. It must provide a path for the entire current. It would be difficult to develop a meter that would handle significant amounts of current. With that in mind, the ammeter uses a shunt to allow some of the current to travel
through a course parallel to the meter. If the shunt malfunctions, it is
likely the meter will not be able to handle the current.
--------------------------------------------------------------------

From this webpage:

http://www.newton.dep.anl.gov/askasci/phy05/phy05159.htm

What it doesn't say is: "the wiring to the meter will not be able to handle the current either."

This is your answer.
If a '66 is like a '64, the shunt, in your case, is the 10 gauge red wire from the starter solenoid to the horn relay.