Preview the prior page first to understand where the engine ground strap is located and how it should be connected. This page is a review of many odd things that can happen if the ground strap is missing or disconnected or has a "dirty" bad contact.

The most common observation or complaint is the engine does not crank over, or cranks very slow. The starter motor is the highest power draw of any electrical device in the car, drawing as much as 200 amps when cranking the engine in the MGA (much more with larger engines). This is not going to work with small wires. It needs a complete circuit from battery + post to battery - post using VERY BIG Wires (battery cables). Part of this electrical path may pass through the chassis frame. That is, the battery ground cable is connected to the frame, and the engine ground cable is also connected to to frame, so the engine starter cranking current does indeed pass through the chassis frame. So if the engine grounding strap is missing or disconnected, where does the cranking current find an alternate return path to the battery ground terminal (or to the car chassis)?

Well, what other metallic and electrically conductive things are electrically connected to part of the engine?

Heater water valve control cable. Throttle control cable Choke control cable Fuel supply hoses (originally metal braid covered) Clutch control hose (if it has a metal braid cover) Gearbox, propshaft, rear axle (to where?)

If the engine ground strap is disconnected, any of these alternate ground paths may (or may not) be sufficient to allow the ignition system to work, but likely none of them is large or robust enough to carry the required high current for the starter motor. End result is abnormally high electrical current passing through one (or more) of these alternate paths returning to body or chassis ground.

Heater valve, and choke cables may be grounded to the dash panel. Throttle cable may be grounded through the throttle pedal linkages. If one of these cables has a good ground connection back to the chassis, it can turn red hot, possibly melt rubber grommets or rubber securing straps or burn the wiring harness were it might touch.

The clutch slave cylinder hydraulic hose (if braid covered) may be grounded to the chassis bracket, or otherwise may be passing high current through the clutch fluid pipe to the master cylinder. That pipe may be a better conductor than the hose braid, so the braid could get hot enough to burn the rubber hydraulic hose.

One possible ground path that may look robust but usually isn't would be the propshaft from gearbox to rear axle. The rear axle is usually electrically isolated with rubber pads on the leaf springs, and rubber hose for the brake line connection (unless it is a braid covered hose). That leaves a possible (but very shaky) path through the parking brake cable, back to the hand lever and tunnel onto the chassis frame, and those things are not designed to carry electrical current either.

As bad as all that sounds, maybe you just stop trying to crank the engine if it doesn't go, and get lucky and not melt or burn anything. For a quick diagnostic you can grab a test light, ground it on the body or chassis, touch it anywhere on the engine, and see if it lights up when you try to crank the engine. A volt meter can serve the same purpose. There should be no light and no voltage. If you get light or any voltage on the engine block or rear plate or starter motor housing, you are missing the engine ground connection.

As a side point, the test light can also be used to diagnose any electrical disconnect (when power is on). You can connect the test light tail alligator clip to a wire end terminal, and touch the test light probe end to the mating connection terminal or screw or body panel or chassis frame. The two mating connection points should always have the same voltage (or lack of voltage), so if it lights up it means you have a lost connection at the mating joint.