SCOTTC COATES wrote:
> Your suggestions are very helpful. I am still wondering
> if there is a diagnostics procedure manual for
> automotive electrical systems that someone can
> recommend since this will be my first foray into
> automotive electrical systems.
I don't have a specific recommendation for a book on this. There
must be some available, but I learned what I know from applying EE
principles to automotive circuits...
> Ken wrote #If your engine is not grounded properly ...# I
> wasn#t clear on grounding of the engine other than the
> battery strap to the negative terminal. I wonder if you
> could elaborate.
Automotive electrical systems are a little different from most
other electrical circuits, in that additional wiring is not
generally used for the "negative terminal" connections, but rather
the engine, body, and frame of the car are used for making the
"ground" portion of most circuits. Accordingly, all electrical
components need to have their "negative" terminal connected to
ground, whether this be the engine, body, or frame. Many
automotive components do this through the casing of the electrical
component. (This typically includes the tail and side marker
lights, horn, various dashboard switches, etc.) To add to the
confusion, these ground connections are not listed on automotive
electrical wiring diagrams, but are assumed.
As you mentioned, the negative battery terminal (at least on
"negative ground" cars, which includes all TR6s) should be
connected to the engine via a ground strap. The engine itself,
however, is electrically isolated from the body and frame, since
all of the engine mountings are made out of rubber. Thus, there
needs to be a ground connection from the engine to the body, in
order to get ground to the body-mounted electrical components. I
am not entirely sure which connection is used for this, but believe
it is a connection from the wiring harness to the body on the right
side of the battery box, near where the heater hoses pass through
the firewall. (I speculate this is located somewhere different on
RHD cars, since the brake/clutch master cylinders would be in that
space...) I have no idea where this wire connects to the engine
itself -- does anybody else know? Or, is there an entirely
different wire somewhere for grounding the engine to the body of
the car?
The other ground connections that are important to the electrical
system are those for the column-mounted components. The steering
column is electrically isolated from the frame and body, so there
is a connection from the wiring harness to the steering rack. (On
LHD cars, this connection is found in the wiring harness to the
headlights/marker lights in the engine compartment at the front
side of the left front wheel arch.) Also, there are wires bridging
the rubber steering column coupling in the engine compartment where
the steering column emerges from the firewall. These wires are
needed for proper functioning of the horn.
In summary, I speculate that your engine to body ground connection
either is corroded, has a bad wire, or is disconnected. Thus, you
are getting a bad ground connection to all components not directly
connected to the engine. Your car still runs fine, however, since
this connection is not needed for the engine-mounted electricals.
--ken
'74 TR6 Daily Driver
Kenneth B. Streeter | EMAIL: streeter@sanders.com
Sanders, PTP2-A001 |
PO Box 868 | Voice: (603) 885-9604
Nashua, NH 03061 | Fax: (603) 885-0631
|