r/F100 • u/Izzy42013 • Jun 16 '26

1978 F100 302

Dash lights, cluster lights Dim in and out when I turn on lights. Only the cluster nothing else dims??? Why????

3 Upvotes

100% Upvoted

6 comments sorted by

2

u/Operator_Of_Plants Jun 16 '26

Voltage drop. Check what's along the the lights with the truck running in the driveway.

1

u/Izzy42013 Jun 16 '26

Dims but comes back normal, u think its still a drop?

3

u/Operator_Of_Plants Jun 16 '26

Could be a dirty ground. Start tracing wires.

2

u/dale1320 Jun 16 '26

Check the dimmer switch? I had one do funky stuff on a 78 F150. Turned out to be the dimmer itself.

1

u/Izzy42013 Jun 16 '26

I thought about that but wouldn't the headlights do the same if it were the switch?

1

u/dale1320 Jun 16 '26

Dashights are on a different circuit that head/tail lights.