# Ignition switch replacement



## jpdriver1 (Jan 6, 2019)

I am replacing the missing ignition switch on the '65 suburban.

Dumb question --- 
the wiring diagram in the manual indicates that the "M" terminal on the switch is connected to the "Primary terminal" on the motor, is the ground bolt on the block? 
If this is the case, where does the battery ground connect? 

Am used to auto systems that use frame grounds and ground straps to firewall. 
thanks 

kevin


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## sixbales (May 18, 2011)

You can connect both battery and switch to a ground bolt on the block. Also connect ground straps to the sheet metal/firewall to ensure grounding.


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## jpdriver1 (Jan 6, 2019)

Great thanks sixbales --- I was leaning that direction, just wanted confirmation.


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## Bob Driver (Nov 1, 2017)

The "M" terminal on the key switch connects to the *MAGNETO* kill circuit on most machines today. I assume a 65 suburban is running a point ignition system (HH80 or HH100 Tecumseh). In that case, the "R" terminal supplies power to the coil (sometimes through a ballast resistor) and the points are on the negative side of the coil and act as switch to ground when the points are closed. The coil fires when the points are opened and the magnetic field in the coil collapses. The condenser acts as an electric "shock absorber" to prevent arching/pitting at the points 

The "M" terminal on a key switch connects to the ground circuit when the key is turned to the off position. Some switches have a separate "G" terminal (ground), if it doesn't, it grounds the through the aluminum housing of the switch case.

I've found the best place to run the main ground is from the battery to the starter mounting bolts if at all possible. It eliminates any ground circuit problems in the start circuit and charge circuit.

Chassis/frame grounds suck on a lawnmower, to much opportunity for rust/corrosion. Everything that needs a good solid ground is attached to the engine, so attaching the main ground cable to the engine is always a better way to go. 

Can't tell you the number of times I've seen bad frame grounds cause problems with a mower. Both Cub Cadet and Troy-Bilt are notorious for being to damn cheap to run a ground cable all the way from the battery box underneath the seat to the actual engine.

When I get a no-crank starting problem with either one the first thing I do is take the black leads on a set of jumper cables and ground battery directly to the engine. About 60% of the time the engine will crank.


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## jpdriver1 (Jan 6, 2019)

Thank you Bob, great info


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## jpdriver1 (Jan 6, 2019)

OK, back again --- 
There are only three terminals on the switch --- no R. 
found the wire for the positive side of coil --- will it hook up to the positive terminal on the switch?


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## Bob Driver (Nov 1, 2017)

So battery voltage in... Battery voltage out.... Ground???

Is it an HH80 (8hp), or HH100 (10hp)? Some of the old HH series Tecumseh were the first to run solid state ignitions (SSI). Be sure you have a round traditional automotive type coil, otherwise it could be an SSI and you DON'T want to screw up that ignition system.... You'll never find the replacement parts

If it has the traditional round automotive style coil, the battery voltage out would go to the (+) side of the coil, or to the ballast resistor if it has one. The points are on the (-) terminal of the coil and act as the switch to ground when the points are closed. Once again, the coil fires when the points OPEN....


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## jpdriver1 (Jan 6, 2019)

HH100, round delco style coil --- 

should the plus side of coil be connected to the battery terminal or the ignition switch? 

sorry to be so dumb


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## Bob Driver (Nov 1, 2017)

Switch... But only if you want to be able to shut the engine off once it starts. Those old HH100's would run forever, but that might be asking a bit much if you wired the coil direct to the battery.


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## jpdriver1 (Jan 6, 2019)

thanks bob


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