Go here:
http://www.brickboard.com/FAQ/700-900/ElectricalStarting.htm

Or to find it manually:
Go to dropdown list at top right corner of these pages, scroll down to 700/900 FAQ. Once there, scroll down for the dropdown lists. Use the one on the left to get to Electrical: Engine Starting, Charging.

Not a fun job but doable.

I'd check everything else first. Including, I'd put two fully charged batteries on the job of starting your engine, jumped together. At your temperatures, even an OK battery might not do the job if the oil is 15/40 or thicker, and/or other negative influences such as iffy cable connections or weak cables etc. etc.
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Sven: '89 245 NA, 951 ECU, expanded air dam, forward belly pan reaches oem belly pan, airbox heater upgraded, E-fan, 205/65-15 at 50 psi, IPD sways, no a/c-p/s belt, E-Codes, amber front corner reflectors, aero front face, quad horns, tach, small clock.