Extra crispy / Tach cable related.

[Wind dog]

Hi guys & gals
Attatched is a picture of what happens when a tach cable shorts out.

This is on a 95 Honda BF25 with tiller steering. The tach is a Tiny Tach self contained unit. I want to stress this was an installlation mistake. The tach has 2 leads, one wrappes around one of the spark plug wires, the other to engine ground. The Tach it's self operated perfectly.
So 71 hours of run time ago, I installed the cable by making another hole in the grommett were the cables pass into the engine. I passed the Tach cable through this hole and tie wrapped the coaxle cable from the tach to the throttle cables to keep it out of the way, bad move, my guess is the tach cable insulation got crushed at the tie wrappes & either shorted internally or to the throttle cables themselves.
Looks like about $100.00 in parts so I guess it could have been worse.

 

[glenn property of pam]

Re: Extra crispy / Tach cable related.

90% sure theres no way a tiny tack did that. The energy required to melt plastic like that would be in the hundreds of amps for a few seconds or a few amps over a long period and the tack only has a tiny battery. I would check your ground cable connection is clean and tight.

 

[Silvertip]

Re: Extra crispy / Tach cable related.

I agree that the tiny tach had nothing to do with this. The metal in the throttle cables has apparently been acting as electrical conductor for the engine electrical system. They got hot and since the tiny tach harness was tied to them, they "took the heat." Check the battery cable connections (both ends of each cable). Bet one of them is loose.

 

[Wind dog]

Re: Extra crispy / Tach cable related.

I don't believe the Tach did it, I believe that the voltage coming down the cable from the spark plug wire (it is an inductive pickup) did it. I don't see how the throttle cables would be carrying any voltage, the only electrical component anywhere near the cables is the kill switch which is very well insulated. I will be checking all connections & the new tach cable will have its own grommetted hole.
Hope I do not come off as arguing with you guys, I respect both of you, just trying to understand the failure.

 

[Silvertip]

Re: Extra crispy / Tach cable related.

Spark voltage is high but current is very low so it would not be the cause either. Any metal can act as a conductor and current will seek a path back to ground anywhere it can.

 

[glenn property of pam]

Re: Extra crispy / Tach cable related.

I don't believe the Tach did it, I believe that the voltage coming down the cable from the spark plug wire (it is an inductive pickup) did it. I don't see how the throttle cables would be carrying any voltage, the only electrical component anywhere near the cables is the kill switch which is very well insulated. I will be checking all connections & the new tach cable will have its own grommetted hole.
Hope I do not come off as arguing with you guys, I respect both of you, just trying to understand the failure.

my "guess" would be that the negative cable is loose or has a bad connection but that would really depend on if the boat was a tinny. A bad cable will cause the negative to hunt a path and if the tiller was a better connection to the hull then it might try to use the cable. Its amazing how poor of a conductor steel is and how fast it will heat up when used as a electrical wire. Its also amazing how electricity seeks the path of least resistance and it what looks like the best path to us is not always the path of least resistance. A simple nylon bushing between the motor and the transom mount can cause the flow to find a easier path.
As for arguing please don't fell put off about speaking your mind as my post starts with "im guessing" or "90% sure" that's code for wow that's odd so we might all learn something new on this one.

 

[Silvertip]

Re: Extra crispy / Tach cable related.

The minute you strap an outboard onto a tin boat the boat and the engine block becomes a current path -- assuming the clamps/bolts manage to get through the paint (and they usually do). This is why a loose negative battery cable can cause an issue like this.

 

[glenn property of pam]

Re: Extra crispy / Tach cable related.

just a quick question. theres nothing that the tiller can touch when the outboard is tilted like a battery terminal?

 

[Wind dog]

Re: Extra crispy / Tach cable related.

I found another clue, on the lower unit at the lower motor mount I found another burnt wire (see picture item#8) I believe this wires purpose is to bond the motor to the mount for corrosion protection? But I should deduce that alot of amps went from boat to the outboard through this wire & the throttle cables. That means, crap I don't know what that means. ;-(

Maybe I should just dust off the Yaks.

 

[Wind dog]

Re: Extra crispy / Tach cable related.

just a quick question. theres nothing that the tiller can touch when the outboard is tilted like a battery terminal?

No chance of that, the batteries are up in the middle of the boat. This is a Tin boat.


I just noticed I never explained what happened leading up to the BBQ.

Was returning to the dock after a half day of trolling in a local lake. Was running at WOT when she started looseing power. I looked back and saw the cable's smoking. I hit the kill button & the engine died, it seems that the sizzling continued for maybe 5/10seconds after shut down. I pulled the cover, looked for anything shorted ( LOL besides the throttle cable) restarted the motor & got back to the dock.

 

[glenn property of pam]

Re: Extra crispy / Tach cable related.

ok that leads to more questions

its happened fast so it means that it required a high amp load and it happened while the motor was running so it probably wasn't the starter. The motor also restarted so even less chance it was the starter on a bad ground.

does the trolling motor have a breaker or fuse with in 6" of the battery terminal
does the boat aux have a breaker or fuse with in 6" of the battery terminal (main feed to fuse panel)
do all batteries have box's to protect the terminals
if all positive wires are fused except for the main starter motor cables then have you checked them for damage

A fuse/breaker should have popped if a wire touched the hull but it sounds like a wire shorted then found a path to negative using the hull and the motor. Check all the wiring as something is wrong. Also check the engine ground just in case

 

[Silvertip]

Re: Extra crispy / Tach cable related.

Bonding wires are used on outboards to electrically bond the powerhead, transom bracket, and the lower unit together. since the power head is mounted on rubber mounts there would be a bonding wire between them. Since the lower unit pivots on the transom bracket that also gets a bonding wire. If one of those bonding wires was burned off or has been obviously heated, that says there is grounding issue somewhere. Current wants to get back to the battery and it is pretty sneaky at how it does that with things aren't right. It "toasts" stuff.

 

[Wind dog]

Re: Extra crispy / Tach cable related.

I found that the connection at the neg battery post was loose last night. ( Duh! It's first thing I should have checked.:facepalm However I saw no signs of arcing?? I'm also confused about the fact that the battery is in a box totally isolated from the hull, so if this loose connection was the cause why would the power jump to the hull if there was no continuity between the hull & battery ground???
Like I said I looked at her a bit last night, all I found was the loose ground, no other chaffed or bare spots, no signs of arcing in any of the battery cables. I also did some testing with the Fluke, I found that with the engine harness disconnected I had no continuity between the ground post & the hull. So that clears all my wiring (?) Once I plug the engine in I do have continuity. This stands to reason since the ground cable on the motor attaches to the block, which is not isolated from the hull.

All my circuit protection is about 3' away from the battery, right now the battery cables to the OB have no protection.:facepalm: I will correct this.Would this http://www.iboats.com/Blue-Sea-ANL-...16324415--session_id.976328784--view_id.37822 in w/ 60amp fuse be suitable for this? The batteries are each in their own box, located mid ship one to port one to starboard.
Tomorrow I'm taking her to my fishing buddies shop,(It's a independent Benz repair shop) he & is boss are going to take a look at her & maybe see what I'm not.
Attached is a wiring diagram.

 

[glenn property of pam]

Re: Extra crispy / Tach cable related.

your battery ground is connected to the motor block and not the transom mount? I have seen some crazy ideas when the cable was not long enough to reach the motor.

 

[Silvertip]

Re: Extra crispy / Tach cable related.

You do not install a breaker or fuse in the large positive battery cable going to the engine on an outboard. One is not needed.

 

[UncleWillie]

Re: Extra crispy / Tach cable related.

...Was returning to the dock after a half day of trolling in a local lake. Was running at WOT when she started loosing power...

...I'm also confused about the fact that the battery is in a box totally isolated from the hull, so if this loose connection was the cause why would the power jump to the hull if there was no continuity between the hull & battery ground??? ...

With the Battery ground intermittent, your primary power source became the Alternator.
Intermittent connections cause the ignition to miss and loose power.
The bonding wires and the throttle cable became temporary (and poor) Ground Paths for the Alternator.

Check both ends of ALL ground wires. There may be more issues.

 

[Wind dog]

Re: Extra crispy / Tach cable related.

Well my fishing buddy & boss checked her out on Friday. They determined that the failure actually happened at start up. It was the only time that there was any current flowing from engine to batteries. The loose cable seems to be the culprit. If my mechanic weren?t me he'd be fired for the loose ground,:facepalm: as it is he got a good talking to.

As was stated before the Tach was collateral damage, the failure was a loose connection at the battery ground. I'd like to stress that the cable was loose in that I could wiggle it side to side, there was no movement up & down so it doesn?t take much to be a bad connection.
I also did not realize that the power would use EITHER battery ground or the water, which ever it can get to.

She's all put back together & ready to go rock fishing this weekend.:joyous: I'm thankful for the new knowledge I've gained, & parts weren't that much so all?s well, I guess.

Thanks to all who responded with their knowledge & advice.