Logo
FULL SITE MENU

Merc 50 starts and runs but stops when I let go of the key

B

bfoker

New member
"I have a 1988-87 mercruiser 5

"I have a 1988-87 mercruiser 5.0 inboard motor that I just purchased used. I was a running take out that I heard run fine. Once I hooked it up in my boat, I turned the key and it started fine, but as soon as I let go of the key, it would shut down. There is a single cut wire that is coming off of one of the posts on the coil. I know it should go somewhere, but where? The previous motor had the Thunderbolt Ignition system but this one does not. I used the existing key switch and motor plug/harness. Any ideas?? Thanks"
 
what color is the wire?
you s

what color is the wire?
you should have power to the coil with the key in the "run " position.
 
"thanks for the reply. the wi

"thanks for the reply. the wire coming off the coil is red, but it was an "after market" so to speak. Looking thru the manual for my other motor, it has it as a white wire going to the 5 hole on the harness. if this is in fact supposed to be in that hole, where can I run it to in order to get my power?"
 
Did you check for 12 vdc at th

Did you check for 12 vdc at the + terminal like the Boat Dr. said? It usually comes off of the elec. choke wire. Look around for the other wire.
 
"i am not familiar with your i

"i am not familiar with your ing. system. however if it is a points system,they typically run a ballast resister and they are usually wired with a FULL voltage startup feature. that is typically run off the starter solonoid (the other small terminal/ not the engine crank terminal). so if your solonoid is providing voltage while cranking it would go away as soon as you let the key return to the run position.

1) run a jumper from battery hot (+) to your coil hot (+) see if its runs correctly. (dont run it like this for long though, your coil will get real hot.

2) if it runs as directed above look for a ballast resister and check continuity. it may be bad or you may have no voltage inn to the resister itself (start chasing wiring)."
 
"could be the ignition switch,

"could be the ignition switch, use a 12v tester at the switch, there should be a post that feeds the switch (B) and the (S) post should have 12v with the key in the ON/RUN position. (usually only 3 wires on the switch)."
 
"Brian is correct

when poin

"Brian is correct

when points were used there was one wire that came from the starter solenoid to the coil + and one wire that came from the wire harness and also went to the coil +.

One wire was for the cranking power to the ignition and the other was for the run power.

With the thunderbolt electronic ignition this "dual" power that is needed when in the "cranking" position at the KEY SWITCH and the "run" position at the KEY SWITCH is all done at the switch.

If you have the know how and a high quality switch you can dissasemble it and clean the contacts. If not buy a new one and be done with it.

Here is a schematic of a easy to make remote starting wire harness that requires 2 switches and some wire and some good alligator clips.

This will allow you to control start and stopping at the engine and eliminate the ingintion switch completely. NOTE!! this is for troubleshooting only and I will not be responsible for the use of this to steal anyones boat....LOL

You do not have to remove any existing wires to use this.

This was needed alot when customers would not leave keys!!!



286457.jpg
"
 
Back
Top