15 replies to this topic

[bikenutmart]

Have a 1972 850 auto, that ive had for some time, but never started, put a freshly charged battery on it yesterday, and I had all he electrics working, all lights, indicators, horn, wipers and heater motor, also had red ignition and orange oil light on when I turned the key to ignition on, I pulled the plugs to give it a spin over and when I turned the key to the start position I lost all the electrics straight away! everything, I checked both fuses and they are fine( new fusebox) I have 12.5v at the solenoid from the main battery cable but only when I disconnect the brown wire that goes to the fusebox, with this left connected I get a weird reading on my meter like 0.6 I think, I'm really confused by this. Could it be the starter solenoid at fault?  Any electrical gurus out there to help? Cheers Mart.

[Wim Fournier]

Clean out the eyelet of the earth cable to the battery and the negative pole on the battery and disconnect the earth cable from the bottom of the trunck. Make the spot on the bottom bright blank and the eyelet of the cable also and connect it again. May be your sorrows are over without spending a dime.

[bikenutmart]

Hi, All the earth cables are new, as is the battery and the earthing points are bright and shiney! Mart.

[Ethel]

It could be the ignition switch itself. Do some hot wiring at its connector instead. Alternatively, you could bridge the solenoid terminal to spin the starter so you don't need to turn the key as far.

[bikenutmart]

Ethel, I could bridge the solinoid terminals to run the starter, but i would still have no ignition to start the car? Mart.

[dklawson]

You said you lost all electrics when you turned the key to the start position.  Does that include the headlights, horn, and courtesy dome light?

 

When you said turning the key to the run position drops to 0.6V, where was that measured between?

[Ethel]

I meant bridge the solenoid while the ignition is on (but not in gear!). It'd only be a work around though, Doug's advice to see if stuff that isn't fed through the ign switch is affected is more useful in finding out if it's the switch or a vicious current drain through the starter.

[gazza82]

... or a jammed starter ...

[bikenutmart]

Doug, Yes, everything including headlights horn and courtesy light, I didn't say turning the key drops the voltage, if you put a voltmeter on the main battery cable at the solenoid it measures 12.8v but only if you disconnect the brown cable to the fuse box, if you leave this attached it goes to 0.6 that is measured between the battery live at solenoid and earth. Cheers Mart.

[bikenutmart]

Gazza, Nope starter is fine as I took it out to check, and it spins nicely, also hooked up a spare battery and jump leads to it and it turns the engine over perfect. Mart.

[gazza82]

But haven't you got other concerns about how it's wired up ie alternator to solenoid? ..

[dklawson]

... disconnect the brown cable to the fuse box,

if you leave this attached it goes to 0.6

that is measured between the battery live at solenoid and earth.

 

There has to be a problem with the main battery cable, its connections, or the engine earth strap.

 

Succinctly, the main battery feed from the boot should attach to one of the threaded solenoid terminals.  (See pic below)

The same solenoid terminal with the battery cable receives ALL the brown wires (and the wire you mentioned coming from the alternator).

The remaining threaded solenoid terminal receives the short, heavy wire going to the starter motor.

 

The brown wires should be "hot" all the time since they connect to the battery cable at the solenoid.

Plugging and unplugging any of the brown wires should NOT make the voltage change much at all.  Consider for a moment that when you crank the engine on the starter motor hundreds of Amps flow through that battery cable and there is still at least 9V on it at the solenoid end.  

 

The solenoid used with the inertia starter is shown on the right in the picture below.  All the brown wires should connect to the terminal marked "battery in".  Obviously the battery cable connects there.  Your solenoid may not have 2 spade terminals (maybe not the white/yellow wire terminal) and the wire on the terminal marked "brown and red" may in fact be white/red.  (Note that in the picture the solenoid mounting foot happens to be pointed "up").

 

You said all the earthing points, battery cables, etc. were new and clean.  With all that said... is there a chance you did not install or the previous owner removed the earth cable from the car body to the engine?  I'm not sure where that would be located on a '72.  It could be a cable between the right inner wing and clutch cover or perhaps from the top engine steady bracket and the engine block.  If the engine earth cable is missing, broken, or making poor contact, the only path for power is through the choke and/or throttle cable.  As you might expect, trying to crank the engine without the engine earth cable in place can ruin both choke and throttle cables.

 

Please confirm what the solenoid wiring and engine earth wiring looks like and post back.

 

Edited by dklawson, 04 March 2016 - 06:47 PM.

[bikenutmart]

Doug, Many thanks for that very detailed reply, haven't had a chance to get in the garage today, but did buy a new engine to body earth strap, will fit this tomorrow and post back with hopefully good news!! Once again many thanks for all the replies. Mart.

[bikenutmart]

Right I fitted the new engine to inner wing earth strap, still the same, checked the earth strap in the boot, the joint to the floor was good and tight, I had checked it, but when I undid it there was paint under the bolt, scraped it away a bit then finished off with some emery cloth, used new bolt done up good and tight and everything works as it should!!! I feel a right numpty for not checking this earlier, goes to show the importance of a good earth!!!! Many thanks for all the help guys. Mart.

[dklawson]

Hi, All the earth cables are new, as is the battery and the earthing points are bright and shiney! Mart.

 

 

....earth strap in the boot,... I had checked it, but when I undid it there was paint under the bolt, scraped it away a bit then finished off with some emery cloth, used new bolt done up good and tight and everything works as it should!!! 

 

It's a good thing you checked this.  Based on your earlier post about the earth points I don't think anyone would have recommended again that you check them.  You may benefit from applying a smear of Vaseline or dielectric grease on the terminals and place you scraped paint off the sheet metal.  It will protect the joint from corrosion for a while.

 

I'm glad you got this sorted and thanks for posting your conclusions.  Now on to the other tasks to get the car back on the road.