Voltage light
 

My 91 base 4x4 22re. When driving at normal speed my lights dim, blower motor slows voltmeter light come on the back to normal back and forth ?

Sometimes worn slipring brushes in the alternator can cause this type of intermittant charge condition, less often, the voltage regulator might be at fault.
Also a check of battery cables and charging wire is in order.

See charging and Alternator system explained and test points on my sig. Use it for a simple, no-cost, quick, practical health check of your charging system, before throwing parts at the problem.

Also check condition of battery. I had leaks around my battery posts, and suspected the posts were not properly connected to cells inside, and causing erratic charging voltage. got battery replaced already. Charging system works fine now.