1985 Merc 260 Intermittent start problem

[Don Brock]

Engine starts and runs for a minute or two then just quits. It may or may not start after that. When it wont start, the symptoms are when key at ON position, the gauges are dead and the oil pressure warning horn doesn't activate. In the START position the engine wont crank. All other electrical accessories work OK. Batteries are good. I can jumper the solenoid and crank the engine.<br /><br />I'm thinking maybe I have a short in the ignition circuit or maybe a bad ground connection, also it occurs to me that a cutout switch is activating. Any thoughts on where to begin troubleshooting?

 

[McKenzie]

Re: 1985 Merc 260 Intermittent start problem

Break out the multimeter! Start with the ignition switch. Check for 12v to the b terminal. Then check for 12v at the I terminal with the key on. Then check for 12v at the I and S terminals when the key is turned to start. Test the continuity of breakers, fuses, and connections. This is unfortunately a tedious job , but nothing a solid hour of tinkering can't fix.

 

[Don Brock]

Re: 1985 Merc 260 Intermittent start problem

Mac,<br />Thanks for the hints. I checked voltages at every terminal on the starter switch and they are all dead. Then I ran a jumper from the battery to the "B" terminal and starting returned to normal. So the task became one of wire tracing and backtracking. In the course of doing that it once again started working by itself. That's infuriating because I still cant trust it, so I keep the jumper wire with me in case of an emergency. Furthermore, I cleaned every plug and connector I could find. In any case it ran good on Sunday, so I'm hoping its fixed. Thanks for the help.