'78 800 won't shut off with the key

[1970Thunderbird]

Hey all,

First of all, thanks to all who helped with my issues regarding my new trigger and stator. I've got it timed right and it fires right up on the first try.

But I now have a new problem: my key no longer shuts off the motor. Everything else seems to work fine, but the key won't kill the motor. I have to choke it out to stop.

Any thoughts? I replaced the internal harness and connected the orange wire to proper place on the switch box. The motor has a mercury switch, and I've done many different wiring combos: orange to mercury switch with a jumper to the switch box, bypassing the mercury switch completely, as well as orange to switch box with a jumper to the mercury switch.

My old harness had the orange wire spliced in two, with one connection leading to the switch box and the other going to the mercury switch. I haven't tried this, as I don't want to splice my new harness unless I have to.

Thoughts?

Thanks!

 

[PHE]

Re: '78 800 won't shut off with the key

You need to check the wire going to the kill switch from the key switch to ground with an ohm meter. The key switch is supposed to ground the kill wire to stop the motor.

 

[1970Thunderbird]

Re: '78 800 won't shut off with the key

Do you mean from the switch box to the harness points? I've done that and it checks ok. I can't timagine there's a problem from the key to the harness connector, as the key worked perfectly until I installed the new internal harness

 

[PHE]

Re: '78 800 won't shut off with the key

Remove the kill wire from the switchbox. Check the wire to ground on the engine using an ohm meter. It should read a short to ground, i.e. zero or close to zero ohms, with the keyswitch off. It should read open, i.e. infinity with the keyswitch in the on position.

 

[1970Thunderbird]

Re: '78 800 won't shut off with the key

PHE,

I tested with battery hooked up. I got ~25ohms with the switch off. I had "overload" or infinity with the switch on.

I take it that means I have either a cut in the line or something else wrong with the wiring?

Thanks

 

[1970Thunderbird]

Re: '78 800 won't shut off with the key

I've tested again. All relevant wires were disconnected during the tests. I tested from the end of the orange wire, all the way up to the switch. It shows 0.5ohms, meaning it's good. I tested the switch ground all the way to the starter solenoid, with the wire disconnected from the solenoid. It, too, shows 0.5ohms. I tested the switch itself, touching the black and orange terminals. When off, it shows 0.0ohms. When the switch is turned on, it shows overload, which is also good.

I'm flabbergasted. The wiring all checks out. The switch checks out. I even ran a jumper wire from the kill terminal, got the motor running, and then touched the jumper to ground, and it killed the motor. And the grounds to the switch box are good.

Could there be anything I'm overlooking? A coworker suggested just splicing in a toggle switch in the orange wire, but I hate to have it look junky.

Thanks for the help.

 

[1970Thunderbird]

Re: '78 800 won't shut off with the key

SOLVED!

The simplest explanation is often the correct one. My switchbox has several wires coming from it that I assumed to be ground wires. Wrong. I connected a jumper from a ground spot on the switchbox to the negative ground on the starter, as I was positive that would ground it.

The key works perfectly know. I also know to never assume. Thanks for all the help. With all the new wiring, the motor cranks on the first try, chokes electrically, runs beautifully, and shuts off when commanded. I'm very much looking forward to really putting it through the paces this weekend.

Thanks so much for all the help. I really appreciate it.

 

[matth121]

Re: '78 800 won't shut off with the key

glad to hear you got it solved, be sure to let us know how it is out on the water.have fun