The Stovebolt Site Forums The Shop Area The Electrical Bay Truck Starts - Truck Won't Stop

Got my 49 1/2 ton started after sitting for 6 months of rehab. Fired on the first try but will only shut off by disconnecting the battery. I'm almost positive the wiring is correct. I put a tester on the switch and with the key out, all three terminals are hot, with the key in switched either way, the battery terminal is hot, the accessory terminal is dead and the ignition terminal is hot but the test light is dim. Can I assume that the switch is bad? Also, when you insert the key, should the cut part of the key be up or down? I may have the switch in upside down but it is still wired correctly. When turning the switch, it seems a little rough and crunchy inside.

If you are putting the test leads from one terminal to another on the switch with wires connected, you may be testing hot lead on one side of the switch to ground on the other side of the switch.

I suggest you disconnect the battery (always a good idea), disconnect the wires from the terminals on the switch, and then test the switch with the key off.

When the key is off, you should not have continuity from the battery terminal to the ignition terminal on the switch. With the key on, you should have continuity from the battery terminal on the switch to all other terminals, depending on the key position.

If you have no continuity on the switch with the key off and the wires removed, something else is wrong. The ignition switch may be bad, in that, once you turn it on you can't turn it off, somewhere you have jumpered around the switch in some way, or some wire(s) are bare of insulation and touching.

With the key off and removed from the switch, do you have power to the gauges? Does the fuel gauge deflect? Does the ammeter deflect? Do you drain the battery after a while?

Glenn, When I tested the switch, I was using each terminal and a chassis ground to check, but you are right, I need to check the switch by itself. Another reason why I am suspicious about the switch is because I have converted to 12 volts and that could have pushed the old switch (probably original) over the edge. I haven't installed my gauges yet (after market) so no information there. I have a new wiring harness, new battery and no other apparent problems. I do have a separate fuse panel connected by a lead from the switch accessory terminal for wipers, heater, etc. It only has power when the switch is off which matches what I found when I tested the switch leads.

My 1954 switches turn on by turning the key counter-clockwise; my 1955+ switches that are for non-foot-start vehicles turn on by turning the key clockwise. Maybe the direction of rotation is part of the problem?

In any case, a bench test of the switch (as suggested above) is the best diagnostic.

Do you know the year and application of your switch (car/truck)? There is usually no problem using a 12v switch in a 6v application (unless it is a 12v switch with a built-in ballast resister being uses in a 6v system - not your situation).

Tim

This is a 49 1/2 ton. I have always assumed that the switch is turned to the right for ignition (clockwise) and to the left for accessory (counterclockwise). I can't tell for sure because in it's current operation, the ignition terminal is hot in all three positions. I'll do a bench test tonight. When I bought the truck, I only drove it about 5 miles before it went in the garage for restoration. I keep thinking that the operation of the switch was odd in the beginning with the original 6 volt system but you could shut the engine off with the switch.

Did you replace the generator with an alternator while it was off the road? If you don't wire an alternator in correctly you can get the unstoppable engine problem. I think there are already posts in the archive on how to fix this problem. I just put a new "universal" ignition switch in my truck; $15 at the local parts store.

Gord

Gord,
I did replace the generator with an alternator. The new wiring harness is pretty straightforward on the new connections but I did have that on my list of possibilities. I'm getting ready to bench test the ignition switch. Hopefully that is the culprit. Beats trying to troubleshoot wiring.

Results Of Bench Test - Same as described in my post above. Just to make sure I didn't have the switch wired wrong, I also tried running the hot wire to each of the three terminals, off position, key out; all three times, the other two terminals were also hot.

I think it's confirmed the switch is bad. Someone please tell me if I'm wrong.

So I guess the next question is: how far can you throw a dead ignition switch? The hole in the dash for the switch on my truck is 1". Your truck probably has the same size. The replacement switch I bought required a 3/4" hole. I had to make a bushing so it would fit. I also had to put a pin in the bushing so the switch won't turn when you turn the key. The switch was also fatter than the old switch - I had to trim the reinforcement that runs along the bottom of the dash to make it fit. I think I set a new world record for longest time to install a switch (my fellow government employees bow down to me). Seriously, try and find a switch for a 1" hole that's not too fat. It will save you time. Some stores have a "no return" policy on electrical parts.

Gord

It's not that hard to find an original ignition switch, and they're REALLY easy to take apart and clean. Briggs and Stratton built those things tough. So far I've built one out of two damaged switches, and have a third that needs a key so I can dismantle it. I'm sure some of those 'bolters who live in rust-free areas and have acres of trucks can help with this one.