Did this to simplify the starting system, but it seems to have solved the occasional no crank and slow crank issue.

Bypass the factory alarm in the starting system.
Connector C274 on the alarm module: short pins 10 and eleven by using a jumper wire carefully connected between the wires feeding those pins.

This eliminates the alarm from the ground path of Starter Solenoid Relay K137, pin 86. This part of the ground path is AFTER the Park/Neutral switch in the auto transmission.

I did this as an attempt to carefuly determine whether I needed a new starter, which I don't as it now cranks well all the time.

This idea came from the electrical troubleshooting manual where it said that in NAS vehicles without an alarm, those pins were shorted.
If there is no alarm not sure why you would have that connector, but the idea worked!
KRMusher

 

Hi, My disco has been periodically not cranking at all when it's hot. Have you had any issues with yours since you bypassed the alarm?

 

mGuy395 - Disco with distributor and plug wires at the front - check ignition amplifier that drives the coil. If newer Disco with coils at back of block, no distributor, they have a crank shaft position sensor, when it gets hot it kills spark. Next time "it" decides to "challenge your vocabulary" plug in a spare spark plug, and lay on mainfold, if no spark when cranking it is usually the CKP. You can pour cold water on it to speed up the return to normal.

 

Have had no trouble with bypassing the alsarm, it cranks like a champ for almost a month.

Savannah's crank sensor check is good. It was lower on my list since this sensor had been replaced about 25k miles ago.

Make sure battery is Disco speced at about 750 CCA.

Was going to replace the starter with URO brand at Rockauto.com, but its enough extra work on the Disco that I decided to troubleshoot as carefully as I could.

Also might want to check the starter soelenoid relay I cited in my post and any connections to starter, solenoid, ground etc.

Good Luck!
KRMusher

 

I want to bypass my alarm , but I can't read the electrical diagrams. Does anyone have the Haynes manual pics labeled?

 

Is this the same as cutting and splicing together the two black wires with orange/red stripes leading from the smaller of the two connectors on back of alarm?