Nissan Repair: Electrical, nissan d21, volt ohm meter

Question
QUESTION: 1991 Nissan D21 pickup 4cly 5spd manual 2wd. The fuse that powers my dash gages and some others keeps blowing. When I replace and just turn the ignition to on the gages come on and bulb check on. If I move the ignition to start without depressing the clutch everything is still on. However when I actually start the engine it blows.

ANSWER: Need you to check the charging system. Check the alternator output. If it reads more than 14.9 to over 15 volts, let me know. If the alternator output is between 13.8 and 14.5 volts, it's normal and we may be looking at a wiring problem.

---------- FOLLOW-UP ----------

QUESTION: 1991 Nissan D21 pickup 4cyl 5spd manual 2wd. I checked the charging system. First I checked the battery before starting. It read 12.8 volts DC. I then started the engine and at idle it read 11.7 volts DC. I revved the engine to about 2.5K rpm and let it go back to idle. I rechecked and it read 13.8 at idle. I have noticed lately that when I start the engine in the morning the lights are a little dim. But when I get out on the road and up to speed they go bright and remain that way. What do you think?
Thanks for your help.

Answer
First of all, you need to check the battery cables. The battery cables and battery poles need to be clean, corrosion free and tight! With a digital volt-ohm meter connected across the battery terminals, record the voltage of the battery. Then, with one meter terminal connected to the ground batt. terminal and the other one connected to the other end of the cable where it ends at the starter read the voltage. It should be the exact same reading of the battery. If not, the cable is defective and it needs to be replaced! The same voltage should be at the alternator cable terminal also. IMPORTANT! Make sure the ground cable is properly grounded and tight! However, I'm pretty sure that the voltage regulator is failing!